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King George Whiting (Sillaginodes punctatus) Fishery
A.J Fowler, R. McGarvey, P. Burch, and J.E Feenstra
SARDI Publication No. F2007/000843-3 SARDI Research Report Series No. 562
SARDI Aquatic Sciences
PO Box 120 Henley Beach SA 5022
July 2011
Fishery Assessment Report to PIRSA Fisheries and Aquaculture
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King George Whiting (Sillag inodes punctatus) Fishery
Fishery Assessment Report to PIRSA Fisheries and Aquaculture
A.J Fowler, R. McGarvey, P. Burch, and J.E Feenstra
SARDI Publication No. F2007/000843-3 SARDI Research Report Series No. 562
July 2011
3
This publication may be cited as: Fowler, A.J., McGarvey, R., Burch, P. and Feenstra, J.E (2011). King George Whiting (Sillaginodes punctatus) Fishery. Fishery Assessment Report to PIRSA Fisheries and Aquaculture. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2007/000843-3. SARDI Research Report Series No. 562. 89pp. South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.sardi.sa.gov.au DISCLAIMER The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Chief, Aquatic Sciences. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it. © 2011 SARDI This work is copyright. Apart from any use as permitted under the Copyright Act 1968 (Cth), no part may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owner. Neither may information be stored electronically in any form whatsoever without such permission. Printed in Adelaide: July 2011 SARDI Publication No. F2007/000843-3 SARDI Research Report Series No. 562 Author(s): A.J Fowler, R. McGarvey, P. Burch, and J.E Feenstra Reviewers: Dr C. Dixon and Dr A. Linnane Approved by: Dr T. Ward Assoc Prof – Wild Fisheries Signed: Date: 28 July 2011 Distribution: PIRSA Fisheries and Aquaculture, SAASC Library, University of Adelaide
Library, Parliamentary Library, State Library and National Library Circulation: Public Domain
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS ............................................................................................................ 8
1. EXECUTIVE SUMMARY ...................................................................................................... 9
2. GENERAL INTRODUCTION ............................................................................................ 11 2.1. Overview ...................................................................................................................................................... 11 2.2. Description of Fishery ............................................................................................................................... 12 2.3. Management Regulations .......................................................................................................................... 14 2.4. Population Biology and Life History ....................................................................................................... 15
3. TRENDS IN COMMERCIAL CATCH, EFFORT AND CPUE ........................................ 18 3.1 Introduction ................................................................................................................................................. 18 3.2 Methods ........................................................................................................................................................ 18 3.3 Results ........................................................................................................................................................... 20 3.4 Discussion .................................................................................................................................................... 41
4. ANALYSIS OF THE RECREATIONAL FISHERY ........................................................... 42 4.1. Introduction ................................................................................................................................................. 42 4.2 Materials and Methods ............................................................................................................................... 43 4.3 Results ........................................................................................................................................................... 45 4.4 Discussion .................................................................................................................................................... 52
5. POPULATION STRUCTURE ............................................................................................. 53 5.1 Introduction ................................................................................................................................................. 53 5.2 Materials and Methods ............................................................................................................................... 54 5.3 Results ........................................................................................................................................................... 55 5.4 Discussion .................................................................................................................................................... 63
6. MODEL ASSESSMENT OF BIOLOGICAL PERFORMANCE INDICATORS ............... 65 6.1. Introduction ................................................................................................................................................. 65 6.2 Results ........................................................................................................................................................... 67
7. ASSESSMENT OF FISHERY PERFORMANCE INDICATORS ...................................... 73 7.1 Introduction ................................................................................................................................................. 73 7.2 Materials and Methods ............................................................................................................................... 73 7.3 Results ........................................................................................................................................................... 75 7.4 Discussion .................................................................................................................................................... 79
8. DISCUSSION ........................................................................................................................ 80 8.1 Context of this assessment ........................................................................................................................ 80 8.2 Determination of stock status .................................................................................................................. 80 8.3 Uncertainty in the fishery .......................................................................................................................... 83 8.4 Management implications .......................................................................................................................... 84 8.5 Future work ................................................................................................................................................. 84
9. REFERENCE LIST .............................................................................................................. 85
10. APPENDIX: MODEL FITS TO DATA .......................................................................... 88
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LIST OF FIGURES
Fig. 3.1 Map of South Australia showing the seven fishery regions for which data are presented in this report (1 = Far West Coast, 2 = Mid West Coast, 3 = Coffin Bay, 4 = Southern Spencer Gulf, 5 = Northern Spencer Gulf, 6 = Gulf St. Vincent, 7 = Kangaroo Island). .................................................................................................................................. 19
Fig. 3.2 Total annual catch and value of the South Australian King George Whiting fishery since 1984. .................. 22
Fig. 3.3 Historical trends in State-wide totals for catch, effort and CPUE for the main gear types used by the commercial fishing sector. Note that it is not possible to provide a State-wide estimate of effort on King George Whiting for hauling nets, which thereby prevents estimating CPUE. ................................................................................. 24
Fig. 3.4 Top graph shows the number of licence holders who could legally take King George Whiting in each year. Bottom graph shows the actual number of licence holders who reported taking some King George Whiting and those who targeted this species in each year. ........................................................................................................................... 25
Fig. 3.5 Monthly estimates of State-wide targeted catch and fishing effort (all gears combined) for the King George Whiting commercial fishery between July 2003 and December 2007. ................................................................................ 25
Fig. 3.6 Far West Coast. Top graph – historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE. The long-term mean for the handline fishery is indicated on each graph. ............................................................................................................................................. 27
Fig. 3.7 Mid West Coast. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type. ..................................................... 29
Fig. 3.8 Coffin Bay. Top graph - historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE by gear type. ......................................................... 30
Fig. 3.9 Southern Spencer Gulf. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type. ......................................... 32
Fig. 3.10 Northern Spencer Gulf. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type. ....................... 34
Fig. 3.11 Northern Spencer Gulf. Top graph - historical trends in hauling net catch for each of the three effort categories. Middle graph - historical trends in hauling net effort for each of the three effort categories. Bottom graph - historical trends in CPUE for each of the three effort categories.......................................................................... 35
Fig. 3.12 Gulf St. Vincent. Top graph – historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE by gear type. ........................................ 37
Fig. 3.13 Gulf St. Vincent. Top graph – historical trends in hauling net catch for each of the three effort categories. Middle graph – historical trends in hauling net effort for each of the three effort categories. Bottom graph – historical trends in CPUE for each of the three effort categories........................................................................................ 38
Fig. 3.14 Kangaroo Island. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type. ......................................... 40
Fig. 4.1 Map of South Australia showing the boundaries of the different geographic blocks used in the National Recreational and Indigenous Fishing Survey (Henry and Lyle 2003). ................................................................................. 44
Fig. 4.2 Comparison of the regional estimates of recreational harvest between the creel survey of 1994/96, the NRIFS of 2000/01 and the South Australian survey of 2008/08. Top graph shows regional harvest of King George Whiting in numbers, bottom graph shows regional harvest in tonnes. ................................................................ 49
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Fig. 4.3 Comparison of the regional catches by the charter boat sector by weight and number of fish harvested for the years of 2005/06 to 2009/10. Note that data collection in 2005 commenced in September, as such data for 2005/06 were for 10 rather than 12 months. ........................................................................................................................... 51
Fig. 4.4 Comparison of the monthly charter boat catches from September 2005 to June 2010, for each of GSV, KI and SSG. ......................................................................................................................................................................................... 51
Fig. 5.1 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Far West Coast of Eyre Peninsula. .................................................................................................................................. 56
Fig. 5.2 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from the Mid West Coast of Eyre Peninsula. .......................................................................................................................... 56
Fig. 5.3 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Coffin Bay, southern Eyre Peninsula. ............................................................................................................................. 57
Fig. 5.4 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Northern Spencer Gulf. ..................................................................................................................................................... 58
Fig. 5.5 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Southern Spencer Gulf. ..................................................................................................................................................... 59
Fig. 5.6 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Gulf St. Vincent. ................................................................................................................................................................. 60
Fig. 5.7 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from MFA 42 in Investigator Strait. .......................................................................................................................................... 61
Fig. 5.8 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Kangaroo Island / Investigator Strait. ............................................................................................................................ 62
Fig. 6.1 Map of South Australia showing the Marine Fishing Areas in which commercial catch and effort are reported, and the 6 spatial cells used in WhitEst, the King George Whiting stock assessment model. ....................... 66
Fig. 6.2 Seasonal variation in biomass and exploitation rate by the recreational and commercial sectors, 2001-2010, for the South Australian King George Whiting population. Monthly WhitEst model-estimated performance indicators of legal biomass, and exploitation rate broken down by sector, are plotted for each of the three main fishery regions. ............................................................................................................................................................................... 70
Fig. 6.3 Yearly State-wide (excluding spatial cell 6) model biological indicators 1984-2010 for South Australian King George Whiting. These performance indicators of (a) yearly recruit numbers, (b) legal biomass averaged over the 12 months of each calendar year, and (c) harvest fraction as the yearly model-estimated catch divided by the yearly average legal biomass, are estimated by the FRDC-sponsored spatial dynamic stock assessment model (WhitEst). Error bars show 95% model estimate confidence intervals. ................................................................................................. 71
Fig. 6.4 Regional yearly model biological indicators 1984-2010 for South Australian King George Whiting. Regions are the West Coast (including Far and Mid West Coast, and Coffin Bay, spatial cell 1 shown in Fig. 6.1), Spencer Gulf (spatial cells 2 and 3), and Gulf St. Vincent and Kangaroo Island (spatial cells 4 and 5). Error bars show 95% confidence intervals. ..................................................................................................................................................................... 72
Fig. 11.1. Fits of model to data monthly commercial catch totals (all gears and target types), for the 5 principal King George Whiting regions. .................................................................................................................................................... 89
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LIST OF TABLES
Table 3.1 Fishery regions considered for the King George Whiting fishery and the Marine Fishing Areas that comprise them (refer Fig. 3.1). ................................................................................................................................................... 19
Table 3.2. Summary of total catch and effort by gear type for each of the seven fishery regions in 2008. (HL=handline, net = hauling net + gillnet). Regions are identified in Table 3.1. ............................................................ 20
Table 3.3. Summary of total catch and effort by gear type for each of the seven fishery regions in 2009. ................. 21
Table 3.4. Summary of total catch and effort by gear type for each of the seven fishery regions in 2010. ................. 21
Table 4.1 Summary of results of catch and targeted effort on King George Whiting, based on the creel survey of the recreational boat fishery through 1994 –1996 (McGlennon and Kinloch 1997). ....................................................... 46
Table 4.2. Summary of results from the National Recreational and Indigenous Fishing Survey for the catches of King George Whiting by South Australian residents in South Australia for the period of May 2000 – April 2001, compared with estimates of the commercial catch over the same time period. ................................................................ 47
Table 4.3 Summary of regional estimates in 2000/01 of harvest and catch by numbers, as well as targeted and non-targeted fishing effort by the recreational sector, as determined by the National Recreational and Indigenous Fishing Survey (Jones and Doonan 2005). .............................................................................................................................. 48
Table 4.4 Summary of regional estimates in 2007/08 of harvest and catch by numbers, as well as targeted and non-targeted fishing effort by the recreational sector, as determined by the South Australian Recreational Fishing Survey in 2007/08 (Jones 2009). ............................................................................................................................................................ 48
Table 4.5 Summary of information used to calculate the total weight per region of the catch of the recreational sector and the comparative estimates of catches for the commercial sector. Recreational data were for November 2007 to October 2008 and commercial data for the financial year of 2007/08 (i.e. July 2007 to June 2008). ............. 48
Table 4.6 Estimates of numbers and weight of King George Whiting harvested by the recreational charter boat sector between 2005/05 and 2009/10. Note that estimates for 2005/06 were for the shortened period of September 2005 to June 2006. .................................................................................................................................................... 50
Table 7.1 Summary of the results of the comparisons between general and biological fishery performance indicators and the limit reference points for the King George Whiting fishery, based on State-wide data. ................ 75
Table 7.2 Comparisons between general performance indicators for 2010 and limit reference points for FWC. ..... 76
Table 7.3 Comparisons between general performance indicators for 2010 and limit reference points for MWC. ... 76
Table 7.4 Comparisons between general performance indicators for 2010 and limit reference points for CB. ........ 76
Table 7.5 Comparisons between general performance indicators for 2010 and limit reference points for SSG. ...... 77
Table 7.6 Comparisons between general performance indicators for 2010 and limit reference points for NSG. ..... 77
Table 7.7 Comparisons between general performance indicators for 2010 and limit reference points for the GSV. .......................................................................................................................................................................................................... 77
Table 7.8 Comparisons between general performance indicators for 2010 and limit reference points for KI. ......... 77
Table 7.9 Yearly biological performance indicators considered in the WhitEst model, for the three regions, and for the State overall. Limit reference points that have been breached are highlighted in yellow. The current performance year covers the period January 2010 – December 2010. ................................................................................ 78
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ACKNOWLEDGEMENTS
We wish to extend our gratitude to the numerous fish processors and fishers who gave us access to
samples of King George Whiting for the collection of data and biological material. In particular we wish
to thank Adelaide’s SAFCOL fish market for their on-going support of the catch sampling program. In
all cases the data on population structure make a significant contribution to our stock assessment work.
The data on catch and effort from the commercial sector of the Marine Scalefish Fishery were provided
to us by Angelo Tsolos of the Information Systems and Database Support Program of SARDI (Aquatic
Sciences). The market sampling was undertaken by Bruce Jackson, Matt Lloyd and Mike Steer. The
report was reviewed by Drs Adrian Linnane and Cameron Dixon from SARDI Aquatic Sciences, whose
comments helped to improve an earlier draft of the report. Comments from Michelle Besley of PIRSA
Fisheries and Aquaculture also improved the presentation of the report. The contributions of all are
acknowledged and greatly appreciated.
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1. EXECUTIVE SUMMARY
1. This is the 8th in a series of stock assessment reports on South Australia’s King George
Whiting fishery since 1997. This assessment comes more than 6.5 years after important
changes were made to the management arrangements in response to a significant down-turn
in the fishery through the period of 1999 to 2002.
2. This report provides an assessment of three types of fishery performance indicators. The
first relates to the State-wide and regional commercial catch, effort and CPUE data by gear
type for the period of 1984 to 2010, adding three years of data since the last assessment.
The second indicator relates to recent estimates of population size and age structures for
numerous localities across the State. Finally, there are estimates of output parameters from
the computer fishery assessment model WhitEst for the period of 1984 to 2010, including
seasonal and annual estimates of recruitment, fishable biomass and exploitation rate.
3. This report also provides a summary of the results for King George Whiting from the three
State-wide recreational fishery surveys including the most recent one completed in 2007/08.
4. The commercial levels of hauling net and gillnet effort on King George Whiting have
declined over time to relatively low levels. As such, emphasis in this report was placed on
analysis of the statistics from the commercial handline sector. Handline catch and effort
decreased between 1992 and 2005, due to the decline in the number of commercial fishers.
However, catch and effort levels largely stabilised during the mid 2000s. The State-wide
estimates of handline CPUE have been variable but nevertheless have increased since the
low period of 1999 to 2002. The majority of regional trends in handline CPUE have been
upward since 2002.
5. The size and age structures determined from market sampling done during 2006/07,
2008/09 and 2009/10 did not differ from the estimates of population structure from the
1990s and early 2000s. As such, there is no evidence for population truncation over the
past decade that is relatable to the fishery.
6. Since 2002, the State-wide estimates of output parameters from the computer fishery model
WhitEst showed strong increases in recruitment and fishable biomass, and the continuation
of decline in the exploitation rate since 1992. Recruitment increased on the West Coast
after 2002, but was stable for approximately 10 years up to 2010 for Spencer Gulf and Gulf
St. Vincent. Fishable biomass increased from 2004 onwards in each region although at
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different rates. Exploitation rate for both the West Coast and Spencer Gulf showed long-
term declining trends since 1992. However, for Gulf St. Vincent, the exploitation rate also
declined from 1992 to 2001, but has subsequently gradually increased.
7. The general fishery performance indicators for 2010 were assessed against limit reference
points from the whole time series back to 1984, at both the State-wide and regional scales.
Breaches of limit reference points at both spatial scales related to the on-going reduction in
total catch and to recent historically high catch rates. In general, these were positive
indicators for the status of the regional fisheries.
8. The biological fishery performance indicators considered from 2010 included fishable
biomass, recruitment and exploitation rates that were estimated using the WhitEst model
for both the State-wide and regional spatial scales. No estimates of fishable biomass
breached the limit reference points. Only for recruitment in Spencer Gulf and exploitation
rate in Gulf St. Vincent were there breaches of limit reference points. The latter reflects the
slowly increasing exploitation rate in this region. These breaches were not cause for
immediate concern.
9. The fourth biological performance indicator considered was population age structure.
There was no evidence that any regional population age structures had changed significantly
over the past decade.
10. The primary uncertainty in our understanding of this fishery relates to the lack of time
series data on catch and effort from the recreational sector despite the new data available
from the survey completed in 2007/08. This means that there remains considerable
uncertainty about the real trends in total catch and exploitation.
11. In general, the fishery indicators suggest that South Australia’s King George Whiting fishery
has been relatively stable for several years, and that there is no immediate need to
reconsider the management arrangements for this fishery.
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2. GENERAL INTRODUCTION
2.1. Overview
Stock assessments have been produced regularly for King George Whiting since 1997 with this
being the eighth report since that time. This report has two aims, i.e. to present information from
the fishery and the biology of the species, and to synthesise this information into an assessment of
the status of the stocks. The last stock assessment report was completed in August 2008, which
reported data that were available up to the end of 2007 (Fowler et al. 2008). This report
incorporates a further three years of commercial catch and effort data, presenting data collected up
to the end of 2010.
This introductory chapter establishes the context for the subsequent empirical and modelling-
based chapters. It provides: a description of the fishery; summarises the management regulations;
and also provides a summary of the population biology and life history of the species based on
research that has been done over the past 30 years or so across southern Australia. Chapter 3
presents a summary of the data from the commercial fishery. This includes the estimates of State-
wide and regional fishery catch, effort and CPUE for the past three years of 2008 to 2010 and
then places these recent data in their historical context based on data collected back to 1984. This
involves a detailed consideration of the regional estimates of catch and effort for the three main
gear types of handlines, hauling nets and gillnets for seven fishery regions.
Chapter 4 summarises the information available on catches of King George Whiting by
recreational fishers, i.e. the results from the recreational boat creel survey that was undertaken in
1994/96 (McGlennon and Kinloch 1997), the National Recreational and Indigenous Fishing
Survey (NRIFS) done in 2000/01 (Henry and Lyel 2003, Jones and Doonan 2005) and the South
Australian Recreational Fishing Survey that was done in 2007/08 (Jones 2009). The regional
recreational catches were compared between surveys and with the commercial catches for the
same periods.
Chapter 5 provides an analysis of the population size and age structures based on samples
collected from across the State by market sampling in 2006/07, 2008/09 and 2009/10. Since the
population characteristics of King George Whiting are so variable spatially and so dependent on
life history processes, it is important that such data be collected regularly every few years to
consider possible size and age truncation and also to update the computer fishery assessment
model.
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Chapter 6 presents the output from the fishery stock assessment model WhitEst that integrates
several types of data from the fishery to output various parameters that indicate the status of the
fishery (Fowler and McGarvey 2000). The input data include: the time series of commercial catch
and effort data; data on recreational catch from both NRIFS (Henry and Lyle 2003) and the
2007/08 State survey (Jones 2009); and regional estimates of population size and age structures
that were collected at various times between 1995 and 2010. The model output includes time-
series of estimates of recruitment, fishable biomass and annual exploitation rate for the three
regions of West Coast, Spencer Gulf and Gulf St. Vincent/Kangaroo Island.
Chapter 7 addresses the second aim of the report, i.e. to determine the status of the King George
Whiting fishery in South Australia. This is done by considering the fishery performance indicators
that are specified in the Marine Scalefish Fishery Management Plan (Noell et al. 2006), and by
comparing the data available for King George Whiting against the prescribed limit reference
points. Chapter 8 also pertains to the second aim of the report. The data from various sources
that were considered in Chapters 3 to 7 are considered in the context of the assessment of
biological performance indicators to determine the status of the fishery at the end of December
2010.
2.2. Description of Fishery
In South Australia (SA), the fishery for King George Whiting is geographically extensive, and
includes all coastal waters from Gulf St. Vincent westwards to Denial Bay, throughout which it is
intensively targeted by recreational and commercial Marine Scalefish fishers. SA’s commercial
fishery makes the highest contribution to the national catch of King George Whiting, which is
generally greater than twice the biomass harvested from Victoria and considerably more than the
catch of Western Australia (ABARE 2010). In South Australia, King George Whiting has
traditionally been the most valuable Marine Scalefish species, but in 2007/08 its total value
dropped to second behind that of Snapper (Knight and Tsolos 2007). However, King George
Whiting remains the highest value species by unit weight.
The King George Whiting fishery in South Australia is a "gauntlet" fishery. Juveniles move from
shallow, protected nursery areas to adjacent deeper water where they become vulnerable to fishing.
The faster growing individuals in each annual cohort reach fishable size during the period of rapid
growth in late summer and autumn when water temperatures are highest. Seasonal levels of
exploitation in the commercial fishery for both handlines and hauling nets peak in late autumn and
winter, when the new recruits are targeted. Monthly catches generally peak in July. In early
summer, when fish reach about 3.5 years of age (based on a birth date of 1st May (Fowler and
13
Short 1998)), movement of young adult King George Whiting located in the two gulfs is directed
southwards. As fish move south they encounter a gauntlet of fishing nets and lines that are used
to target these young adults, resulting in high levels of exploitation. The survivors that reach the
southern, deeper, offshore spawning areas at and near the mouths of the two gulfs replenish the
populations of larger, older fish (Fowler et al. 2000a, Fowler et al. 2002).
The fisheries in Gulf St. Vincent, Northern Spencer Gulf and the West Coast bays predominantly
take relatively small, young, immature fish of about 3 years of age that are quite close to the
minimum legal size, while fish on the spawning grounds tend to be larger and older, with some up
to 18 years of age. Analysis of the reproductive activity of adult fish during the time of spawning
in different regions of the two gulfs indicated that King George Whiting of comparable size and
age showed no evidence of spawning activity in the northern regions, but nearly all those found in
the southern aggregations, regardless of size, showed evidence of active spawning (Fowler et al.
1999, Fowler et al. 2000a). This indicated that spawning in the gulfs is confined to southern areas,
which means that the reproductive sustainability of such populations is determined by successful
persistence of resident populations in these spawning areas. These spawning sub-populations of
larger, older fish are replenished annually by immigrants of 3-4 years of age that come from
inshore fishing grounds and the upper gulfs (Fowler et al. 2000a, Fowler et al. 2002). Historically,
the exploitation of spawning aggregations was relatively low, which may have accounted for the
stable recruitment of King George Whiting over the years for which catch data were available
(Fowler and McGarvey 2000, McGarvey et al. 2000). However, anecdotal reports suggest that
with a developing charter boat fishery and an expanded range offshore of the commercial and
recreational sectors, it is possible that fishing pressure on the spawning aggregations has increased
in recent years.
The commercial sector of the Marine Scalefish fishery uses a variety of gear types of which
handlines, hauling nets and gillnets are the principal ones for targeting King George Whiting.
Recreational fishing for King George Whiting is by hook and line, principally from boats.
14
2.3. Management Regulations
Changes to the management regulations for the South Australian King George Whiting fishery
were implemented in October 2004. These included: (1) an increase in legal minimum length
(LML) from 30 to 31 cm in all waters east of longitude 136°E; (2) the daily recreational bag limit
was reduced from 20 to 12 legal-size fish per person, with the boat limit reduced from 60 to 36
fish per boat; (3) the existing licence amalgamation scheme was enhanced by reducing the number
of points needed to acquire an amalgamated licence (from 26 to 24); (4) also, if a non-licensed
person was detected in possession of more than 75 King George Whiting, which is considered a
commercial quantity, then that person may be guilty of an offence. At that time, consideration of
appropriate management options were informed by management simulations that were undertaken
using the simulation model WhitSim that tested a range of different strategies. The results of
these had previously been summarised in an earlier stock assessment report (McGarvey et al.
2003).
The principal means of effort control in the commercial sector is ‘limited-entry’. Since 1994, a
licence amalgamation scheme has been operating to reduce effort in this sector and to remove
latent effort from the fishery. As a consequence, the number of commercial Marine Scalefish
licences (‘M’ and ‘’B’ class) has fallen from 701 in 1984 to 346 in 2011. Also, the use of devices in
the commercial sector is strongly regulated by a complex suite of input and output controls. This
includes hauling nets that must have a mesh size of less than 15 cm, a maximum length of 600 m,
a maximum drop of 5 m in the wings and 10 m in the bunt or pocket. Their use is restricted to
waters of less than 5 m depth, and is banned within half a nautical mile of any officially recognised
artificial reef and within a radius of 100 m of any jetty, wharf or pier. Gillnets cannot be used in
waters shallower than 5 m, the mesh size must be between 5 cm to 15 cm, with a maximum length
of 600 m and a maximum drop of 5 m. Handlines are limited to 2 per person, with a limit of 3
hooks per line. There are limits on the number of agents that can fish from a licence, the master
of the licence must be an owner operator. There are also many permanent and seasonal netting
closures that have been introduced over the years for a variety of reasons including the protection
of nursery areas and spawning grounds (Noell et al. 2006). A significant rationalisation of the net
sector was undertaken in 2005 when a net licence buy-back scheme resulted in the reduction of 61
net licences and endorsements from 113 to 52 (24 full net licences were removed, and 37 net
endorsements [hauling nets and gillnets] were removed from licences). This resulted in the
removal of approximately 45% of net fishing effort. At that time, further permanent spatial
closures to the net fishery were also implemented in large parts of the State’s inshore waters.
15
Previous significant management changes include a reduction in the recreational bag limit from 30
to 20 fish.day-1 or from 90 to 60 fish.boatday-1 in September 1994. This was followed by an
increase in the LML from 28 to 30 cm TL for both commercial and recreational sectors in
September 1995 (Fowler and McGarvey 1997).
2.4. Population Biology and Life History
Although the general life cycle of King George Whiting has been known for a number of years
(Jones et al. 1990), our understanding of it was further enhanced through FRDC project 95/008
(Fowler and McGarvey 2000). That study synthesised information on population age structures,
adult movement patterns, reproductive biology, characteristics of recruitment and genetic
structure to develop a comprehensive picture of the life history and stock structure of this species
in South Australia.
The nursery areas for recruitment of King George Whiting are shallow, protected bays where the
post-larvae arrive during the winter and spring in each year. Important nursery areas include
Barker Inlet, Franklin Harbor, and the West Coast bays. Juveniles reside in these nursery habitats
for a year or two before they move out into gulf waters or deeper areas of the West Coast bays,
which are characterised by broken, low-profile reef and stands of seagrass (e.g. Posidonia spp.)
(Jones et al. 1990).
When the fish reach 3-4 years of age they are capable of moving distances of up to several
hundred kilometres within a few months (Fowler and McGarvey 1997, Fowler and March 2000,
Fowler and McGarvey 2000, McGarvey and Feenstra 2002, Fowler et al. 2002). They migrate
from nursery areas to spawning grounds, whilst there are also less directed movements among
coastal areas, mostly along the coast. Fish from Gulf St. Vincent and northern Spencer Gulf
move the greatest distances, generally in a net southerly direction. Some fish tagged in Gulf St.
Vincent have been recaptured along the north coast of Kangaroo Island; some from northern
Spencer Gulf have been recaptured principally in Hardwicke Bay in the south-east, whilst some
have been found around the islands of the south-western part of the gulf; those from West Coast
bays have rarely been recaptured, but are thought to end up around offshore shoals and islands.
In contrast, fish tagged near Kangaroo Island and southern Spencer Gulf did not move far and
showed no systematic directional displacement (Fowler and McGarvey 1997, 1999; Fowler and
March 2000; Fowler et al. 2002). These different movement patterns influence population
structure. In those source areas from where fish move and where fishing is concentrated,
population structure is generally truncated, consisting of small fish from a few young age classes.
By contrast, at destination locations, many older age classes are well represented with some fish up
to 18 years of age (Fowler et al. 1999, Fowler et al. 2000a).
16
Spawning occurs at the offshore grounds to which fish migrate, including: Investigator Strait along
the north coast of Kangaroo Island; the south-eastern tip of Yorke Peninsula in Gulf St. Vincent
(Tapley Shoal); and south-eastern Spencer Gulf around Corny Point and Wardang Island.
Spawning typically occurs between March and May (Fowler et al. 1999, Fowler et al. 2000a).
Patterns of larval distribution (determined by plankton sampling during the 1980s (Bruce 1989))
provided further evidence that spawning occurs in the southern locations and that larvae are
advected northwards into the gulfs (B. Bruce unpublished data). To date, the spawning areas
responsible for replenishing the West Coast bays have not been determined. Commercially-
harvested fish from the West Coast bays display minimal gonad maturation suggesting that
spawning may occur further offshore from these fishing grounds.
The long pre-settlement duration of 80 to >120 days of larval King George Whiting (Fowler and
Short 1996) would be expected to provide ample opportunity for advection over long distances by
hydrodynamic processes, as is the case for the Victorian populations (Jenkins et al. 2000). In Port
Phillip Bay, Victoria, the inter-annual variation in post-larval abundance is strongly correlated with
the strength of the zonal westerly winds that presumably influence the rate of transport of the
larvae. This influences recruitment success and productivity to the fishery several years later
(Jenkins 2005). Because of this, it is possible that spawning by the South Australian stock
ultimately replenishes the populations of King George Whiting in Port Phillip Bay, Western Port
and Corner Inlet, i.e. the places where this species is commercially fished in Victoria. In contrast,
however, hydrodynamic modelling for the coastal areas around South Australia suggests that King
George Whiting larvae are advected over only relatively short distances of 50-100 km (Fowler et
al. 2000b). This suggests that the South Australian populations are sustained by local spawning.
The hydrodynamic modelling suggested the existence of relationships between particular spawning
locations and nursery areas separated only by 100-200 km. Furthermore, the combination of
hydrodynamic modelling, sampled larval distributions, and adult movement patterns suggest that
the two gulfs are largely-distinct, self-sustaining populations. Nevertheless, analysis of stock
structure based on mitochondrial DNA and microsatellite primers found no significant
phylogeographic structure across the distribution of King George Whiting (Haigh and Donnellan
2000). This is consistent with its long pre-settlement duration, and does not counter the above-
mentioned subpopulation model since only a minimal but consistent exchange of individuals (two
or three fish per year) between subpopulations is sufficient to maintain them as genetically
homogeneous (Taylor and Dizon 1996).
Several studies have focussed on the diets of King George Whiting. The stomachs from post-
larvae that were collected from shallow seagrass beds contained mobile crustacea, primarily
17
calanoid copepods and to a less extent benthic harpacticoid copepods with benthic amphipods,
cyclopoid copepods and cladocerans in low numbers (Moran et al. 2004). That study also revealed
benthic prey items in the stomach contents of post-larvae collected by plankton tows done
adjacent to seagrass beds, which suggests the likelihood of secondary planktonic dispersal of post-
larvae after settlement. In an earlier study, Robertson (1977) had considered the diets of King
George Whiting in the shallow, mud, tidal flats of Western Port, Victoria. The diet of the very
young 0+ fish was predominantly made up of harpacticoid copepods, gammarid amphipods and
Mysidacea, which are abundant in the seagrasses associated with the mudflats. Later, the diet of
the 0+ fish was dominated by larvae of the ghost prawn Callianasa australiensis, whilst polychaete
worms and juvenile sentinel crabs also became incorporated into the range of prey. A total of 26
food types were taken by the 1+ and 2+ age groups, but the diets were dominated by six prey
categories: several types of polychaete worms; the ghost prawn; amphipods and the juvenile
sentinel crab Macrophthalmus latifrons. Another study done in Wilson Inlet in Western Australia
considered the diet of a broad size range of individuals (Platell et al. 2006). It determined that the
major components of the diet were polychaete worms that were found in 65% of the guts
considered, and contributed to 57% of the overall dietary volume. Polychaetes were ingested by
individuals of all length classes but the volumetric contribution to the diet was greatest in the
smallest fish, i.e. 25-124 mm. The contribution to the diet of large crustaceans declined from the
175-224 mm size class to the larger fish. Alternatively, bivalve siphons and neogastropods were
found only in the guts of fish >225 and >275 mm, respectively.
18
3. TRENDS IN COMMERCIAL CATCH, EFFORT AND CPUE
3.1 Introduction
Since 1984, commercial fishers in South Australia’s Marine Scalefish Fishery have been required to
submit, on a monthly basis, a catch return that relates their catch and effort data for the preceding
month. These data now provide a data time-series that constitutes the most fundamental dataset
that is available as an indicator of the status of the fishery. These commercial statistics are
examined here at two spatial scales; State-wide and regional. In this chapter the data were
examined qualitatively, whereas in Chapter 7 they were used to calculate general fishery
performance indicators that were compared against limit reference points. Furthermore, the catch
and effort data reported here were also used in the fishery assessment model, WhitEst, to calculate
time-series of output parameters that relate to population processes and to fishery status (Chapter
6). These output parameters are assessed against limit reference points to indicate the status of the
fishery (Chapter 7).
3.2 Methods
For this stock assessment on King George Whiting the catch and effort data were accumulated
across fishers to provide regional, annual totals of catch and effort by gear type, which were then
used to calculate annual estimates of catch per unit effort (CPUE) for each region. The data for
the three main gear types, i.e. handlines, hauling nets and gillnets were considered here for the
seven regions shown in Fig. 3.1 that are comprised of the Marine Fishing Areas identified in Table
3.1. The presentation of data was limited by constraints of confidentiality, i.e. data could only be
presented when summarised from five or more fishers. Because of declining effort in the net
sector there are such confidentiality issues with respect to the data for some regions, whilst for
others there has been no meaningful net effort for a number of years. Consequently, the data for
the net sector are only presented here for the regions that include the two northern gulfs, i.e. NSG
and GSV.
With respect to fishing effort, data are reported as fisherdays, which relate to the number of days
fished and number of personnel involved, i.e. if there were two fishers on board a vessel for a day
of fishing then this counted as two fisherdays. There are two components of fishing effort for
each gear type, i.e. targeted and untargeted effort. For handlines and gillnets, total effort was
estimated from targeted effort that was scaled upwards by the proportional additional catch that
19
was taken by untargeted effort. Thus, for handlines and gillnets it was possible to provide annual
estimates of total catch and effort and associated estimates of CPUE. However, for hauling nets
the situation is more complex because fishers may catch substantial numbers of King George
Whiting whilst targeting other species, or when not targeting any species in particular. Under such
circumstances it is not possible to determine the targeted effort that was directed specifically at
King George Whiting, making it impossible to provide a direct estimate of targeted CPUE.
Consequently, for hauling nets, estimates of catch, effort and CPUE are reported for three
different fishing effort categories: targeted effort; effort targeted at other species; and effort not
directed at any particular species.
4443
22
1716
40
36
11
4948
1617
3034
9
108
15
27
28
39 41 42
35
33
32
23
21
29
7
31
18
20
11
19
1617
35° S
33° S
0
SCALE (km)
100
1 2
34
5
6
7
134° E 136° E 138° E
Fig. 3.1 Map of South Australia showing the seven fishery regions for which data are presented in this report (1 = Far West Coast, 2 = Mid West Coast, 3 = Coffin Bay, 4 = Southern Spencer Gulf, 5 = Northern Spencer Gulf, 6 = Gulf St. Vincent, 7 = Kangaroo Island).
Table 3.1 Fishery regions considered for the King George Whiting fishery and the Marine Fishing Areas that comprise them (refer Fig. 3.1).
Region name Marine Fishing Areas Far West Coast (FWC) 07, 08, 09, 10 Mid West Coast (MWC) 15, 16, 17, 18 Coffin Bay (CB) 27, 28 Southern Spencer Gulf (SSG) 29, 30, 31, 32, 33 Northern Spencer Gulf (NSG) 11, 19, 20, 21, 22, 23 Gulf St. Vincent (GSV) 34, 35, 36, 40, 43 Kangaroo Island (KI) 39, 41, 42, 44, 48, 49
20
3.3 Results
Commercial fishery statistics in 2008, 2009 and 2010
Commercial catches by region and gear type for each of 2008, 2009 and 2010 are presented in
Tables 3.2, 3.3 and 3.4, respectively. The total State-wide catches increased from 313,147 kg in
2008 to 358,121 kg in 2009 and then back to 326,532 kg in 2010. Handlines were the dominant
gear type in each year, with the proportional contribution ranging from 79.8% in 2008 to 83.0% in
2009. The percentage of total catch taken by hauling nets fell from 14.4% in 2008 to only 9.7% in
2010. Gillnets accounted for from 3.0 to 3.6% of the total catch. In each year the total catch was
highest on the Far West Coast, with Southern Spencer Gulf consistently the second most
significant region (Tables 3.2, 3.3, 3.4). Also, in each year Coffin Bay provided the lowest total
catch of all seven regions.
Between 2008 and 2010, the total handline fishing days ranged from 13,836 to 14,456 (Tables 3.2-
3.4), which are totals that are marginally lower than those reported for the period of 2005-2007
(Fowler et al. 2008). The numbers of gillnet fishing days were very low compared to handlines,
having fallen to only several hundred fishing days per year (not shown in tables for confidentiality
reasons).
Table 3.2. Summary of total catch and effort by gear type for each of the seven fishery regions in 2008. (HL=handline, net = hauling net + gillnet). Regions are identified in Table 3.1.
Region no.
Region Total catch by HL (kg)
Total catch by net (kg)
Total catch (other gears)
Grand total catch
Total effort HL (fisher-days)
1 FWC 89,238 714 333 90,285 4,833 2 MWC 27,158 0 0 27,158 1,472 3 CB 12,862 0 41 12,903 589 4 SSG 68,110 2,908 1,971 72,989 3,462 5 NSG 12,244 23,602 838 36,684 752 6 GSV 13,291 21,362 2,306 36,959 1,062 7 KI 26,997 7,637 1,535 36,169 1,666 Total 249,900 56,223 7,024 313,147 13,836
21
Table 3.3. Summary of total catch and effort by gear type for each of the seven fishery regions in 2009.
Region no.
Region Total catch by HL (kg)
Total catch by net (kg)
Total catch (other gears)
Grand total catch
Total effort HL (fisher-days)
1 FWC 98,474 497 542 99,513 4,334 2 MWC 53,983 0 4 53,987 2,066 3 CB 13,132 0 5 13,137 538 4 SSG 76,640 3,782 1,694 82,116 3,856 5 NSG 12,453 21,751 286 34,490 792 6 GSV 12,979 11,798 5,625 30,402 1,050 7 KI 29,476 8,338 6,662 44,476 1,820 Total 297,137 46,166 14,818 358,121 14,456
Table 3.4. Summary of total catch and effort by gear type for each of the seven fishery regions in 2010.
Region no.
Region Total catch by HL (kg)
Total catch by net (kg)
Total catch (other gears)
Grand total catch
Total effort HL (fisher-days)
1 FWC 90,885 527 127 91,539 4,587 2 MWC 40,391 0 0 40,391 1,868 3 CB 14,498 0 63 14,561 615 4 SSG 72,517 4,941 2,087 79,545 3,758 5 NSG 8,329 16,925 53 25,307 536 6 GSV 11,148 13,970 8,909 34,027 850 7 KI 26,612 7,252 7,298 41,162 1,964 Total 264,380 43,615 18,537 326,532 14,178
Trends in commercial catch and effort
The commercial fishery statistics from 2008 to 2010 contribute data for a further three years to the
long-term trends reported previously (Fowler et al. 2008). The estimates of State-wide commercial
catch of King George Whiting decreased substantially from 1984 to 2004, but have remained
relatively consistent since then (Fig. 3.2). From 1984 to 1992, catch was variable, showed no long-
term trend, and culminated in the highest ever annual catch of 776 t in 1992 (Fig. 3.2).
Subsequently, catch decreased and stabilised at 550-600 t.yr-1 until 1999, before dropping to less
than 450 t.yr-1 in 2000. It dropped again to 370-380 t.yr-1 in 2002 and 2003, and has been
consistent at 300-350 t.yr-1 between 2004 and 2010. In 2008 and 2010, the total catches were the
lowest and 2nd lowest yet recorded. The commercial catch of King George Whiting in 2008 was
47.9% lower than that taken in 1999 and 59.6% lower than that of 1992, which were two years
when maxima were recorded.
The estimates of the value of the annual commercial catch of King George Whiting have varied
considerably over time. The annual value increased from its lowest value in 1984 to its highest in
22
1995. Since then it has varied from $3.9 to $5.2 million, but with no long-term trend. The
estimated values of $5.2 and $4.9 million in 2009 and 2010 were high given the relatively low
catches taken.
0
1000
2000
3000
4000
5000
6000
0
100
200
300
400
500
600
700
800
90019
84
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Total catch
Value
Cat
ch (t
onne
s)
Valu
e ($
,000
)
Fig. 3.2 Total annual catch and value of the South Australian King George Whiting fishery since 1984.
Since 1984, handlines have been the dominant gear type in the commercial fishery (Fig. 3.3).
Between 1984 and 1999, handline catch varied around 400 t.yr-1, with no obvious long-term trend.
However, since then, handline catch has dropped from 426 t in 1999 to 264 t in 2010, i.e. a drop
of 38%, with a decline since 1992 of 42.6%. Hauling nets remain the second most significant gear
type for taking King George Whiting despite that catches have decreased systematically since the
record catch taken with this gear in 1992. The hauling net catch of 32 t recorded in 2010 was the
lowest yet recorded representing a decrease of 88% since 1992. The total State-wide gillnet catch
has always been below 50 t.year-1, but has continued to decline over the years and in 2010 had
fallen to only 12 t.
Handline effort on King George Whiting has decreased from 31,235 fisherdays in 1992 to 14,177
fisherdays in 2010, i.e. a reduction of 54.6% over this 18 year period (Fig. 3.3). Gillnet effort has
declined from 2,523 to only 323 fisherdays over the same period. Such decreases in effort reflect
the declining trend in number of licence holders in the commercial fishery, which accelerated after
1994 when the licence amalgamation scheme was introduced and in 2005 through the net buyback
(Fig. 3.4). Consequently, over the years there has been a considerable decrease in numbers of
commercial fishers who targeted and/or caught King George Whiting (Fig. 3.4). The number of
Rock Lobster fishers who retain access to fish for King George Whiting has been relatively
consistent for numerous years.
23
The estimates of State-wide CPUE for handlines and gillnets have been variable, but nevertheless
have generally trended upward over time (Fig. 3.3). The trend for handlines is divisible into two
time periods. It increased relatively consistently from 1984 to 1999, but then dropped noticeably
in 2000 and then again in 2002. Since then, CPUE has gradually increased although with minor
decreases in both 2008 and 2010. The highest average CPUE ever recorded was 20.6 kg.
fisherday-1 in 2009. Since the early 2000s, CPUE has increased dramatically in the gillnet fishery,
but these estimates are based on very low levels of catch and effort and so may not provide a good
indication of fishable biomass.
Seasonality of catch
The seasonality of the State-wide commercial catch of King George Whiting is apparent from
monthly catch totals (Fig. 3.5). For the period of July 2003 to December 2010, monthly catches
were highest during winter, and dropped to annual minima in summer. The monthly estimates for
targeted effort on King George Whiting were highest from March through to September, but were
particularly low in each year between November and January.
24
0
100
200
300
400
500
600
700
800
900
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Total catch
Gillnet
Handline
Haulnet
0
5000
10000
15000
20000
25000
30000
35000
40000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Handline
Gillnet
0
5
10
15
20
25
30
35
40
45
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Gillnet
Handline
Cat
ch (t
onne
s)E
ffort
(fish
erda
ys)
CP
UE
(kg.
fishe
rday
-1)
Fig. 3.3 Historical trends in State-wide totals for catch, effort and CPUE for the main gear types used by the commercial fishing sector. Note that it is not possible to provide a State-wide estimate of effort on King George Whiting for hauling nets, which thereby prevents estimating CPUE.
25
0
100
200
300
400
500
600
70019
83
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
Taking KGW
Targeting KGW
Num
ber o
f lic
ense
hol
ders
0
100
200
300
400
500
600
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
'M' class'B' classRock lobster
Fig. 3.4 Top graph shows the number of licence holders who could legally take King George Whiting in each year. Bottom graph shows the actual number of licence holders who reported taking some King George Whiting and those who targeted this species in each year.
0
500
1000
1500
2000
2500
0
5
10
15
20
25
30
35
40
45
50
Jul-0
3
Jan-
04
Jul-0
4
Jan-
05
Jul-0
5
Jan-
06
Jul-0
6
Jan-
07
Jul-0
7
Jan-
08
Jul-0
8
Jan-
09
Jul-0
9
Jan-
10
Jul-1
0
Target catch Target effort
Cat
ch (t
onne
s)
Effo
rt (fi
sher
days
)
Fig. 3.5 Monthly estimates of State-wide targeted catch and fishing effort (all gears combined) for the King George Whiting commercial fishery between July 2003 and December 2007.
26
Regional Catch and Effort Statistics
The remainder of this chapter provides a summary of the catch, effort and CPUE data from 1984
to 2010 for each of the seven fishery regions identified in Table 3.1 and Fig. 3.1. For each region,
estimates of total catch are presented for the gear types that make a considerable contribution to
total catch, i.e. primarily handlines, but for some regions also hauling nets and gillnets. Estimates
of total effort and CPUE are provided for handlines and also for gillnets for some regions. For
NSG and GSV, i.e. the two regions in the northern gulfs where hauling nets remain a significant
gear type, a separate figure is also provided that relates the region-specific estimates of catch,
effort and CPUE for where effort was reported as ‘targeted’, ‘no specific species targeted’ and
‘other species targeted’.
Far West Coast (Denial and Streaky Bays)
The annual catch from the bays of the Far West Coast is usually the highest of all regions across
the State (Tables 3.2-3.4). The catch in this region has historically been dominated by the handline
sector since the implementation of a netting ban in 1958. The handline catch from the Far West
Coast reached a peak of 150,455 kg in 1989 after which it declined consistently to 108,045 kg as
recorded in 1998 (Fig. 3.6). It was then highly variable through the period of 1999 to 2002, but
has gradually declined since then. The handline catch of 90,885 kg in 2010 is the 3rd lowest yet
recorded. Between 1984 and 1997, handline effort declined by 40% to approximately 6,000
fisherdays.year-1 (Fig. 3.6). It then increased again in 1999, but has gradually declined since then.
Targeted handline effort declined by 28.2% from 6,384 fisherdays in 2004 to 4,587 fisherdays in
2010.
Handline CPUE showed a long-term increasing trend through the period of 1984 and 1999 (Fig.
3.6). Through this period there were several notable peaks, one from 1989 to 1992 and the second
from 1996 to 1999. Handline CPUE then declined considerably through the period of 1999 to
2002. Since then, it has gradually recovered and in 2009 attained the highest level ever recorded of
22.7 kg.fisherday-1 before falling back to 19.8 kg.fisheryday-1 in 2010. Clearly, handline CPUE has
increased between 1984 and 2010, but the increase has not been consistent over time.
27
020000400006000080000
100000120000140000160000180000200000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Cat
ch (k
g)
Handline
0
2000
4000
6000
8000
10000
12000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Effo
rt (fi
sher
days
)
0
5
10
15
20
25
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
CPU
E (k
g/fis
herd
ays)
Far West Coast
Fig. 3.6 Far West Coast. Top graph – historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE. The long-term mean for the handline fishery is indicated on each graph.
28
Mid West Coast (Baird and Venus Bays)
The total annual catch from the bays of the Mid West Coast is generally considerably less than that
from the Far West Coast (Tables 3.2 - 3.4). Handlines, gillnets and hauling nets have each
historically contributed to the catches in this region in order of decreasing significance. Prior to
2005, Baird Bay and half of Venus Bay were closed to net fishing whilst in August 2005, the
remaining part of Venus Bay was also closed to net fishing. As such, since 2005 these bays have
only been accessible to line fishing.
The annual handline catches from the bays of the Mid West Coast have generally been highly
variable from year-to-year (Fig. 3.7). In 2000, the catch dropped to the lowest recorded level and
remained low in both 2001 and 2002 when the estimates were 14,395 and 13,226 kg, respectively.
Since then, handline catch has continued to be variable but nevertheless has increased
considerably. Handline effort has also been highly variable from year-to-year but has
demonstrated a significant and accelerating long-term decline, particularly through the period of
1999 to 2002, culminating in the lowest recorded fishing effort in 2001 and 2002 of 1,251 and
1,065 fisherdays, respectively (Fig. 3.7). Subsequently, handline fishing effort has gradually
increased and in 2010 was at 1,868 fisherdays. Between 1984 and 2000, handline CPUE was quite
variable by virtue of the highly variable annual catch and effort data and showed no long-term
trend (Fig. 3.7). However, after 2000, handline CPUE has been less variable, rising from a low
level of 7.8 kg.fisherday-1 to a maximum of 26.1 kg.fisherday-1 in 2009, before falling back to 21.6
kg.fisheryday-1 in 2010.
Coffin Bay
As a consequence of a review of the net fishery in 1995 and 1996, Coffin Bay was closed to net
fishing in 1996. As such, this region has effectively been a line fishery since then.
From 1984 to 2000, the handline catch of King George Whiting was highly variable but
nevertheless showed no long-term trend (Fig. 3.8). From 2000 to 2005, it declined annually to just
6,121 kg and has since recovered to 14,498 kg in 2010. The temporal variation in fishery catches is
also reflected in the trends in effort (Fig. 3.8). There was considerable decline until 2005, after
which it has increased from a minimum of 316 fisherdays in 2005 to 615 fisherdays in 2010.
Handline CPUE has been variable but has nevertheless increased generally over time (Fig. 3.8).
Since 2006, it has been higher than 20.0 kg.fisherday-1, and was 23.6 kg.fisherday-1 in 2010, the
third highest yet recorded.
29
Mid West Coast
0
20000
40000
60000
80000
100000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Cat
ch (k
g)
Handline
0
500
1000
1500
2000
2500
3000
3500
4000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Effo
rt (fi
sher
days
)
0
5
10
15
20
25
30
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
CPU
E (k
g/fis
herd
ays)
Fig. 3.7 Mid West Coast. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type.
30
0
5000
10000
15000
20000
25000
30000
35000
40000
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Cat
ch (k
g)
Handline
0
500
1000
1500
2000
2500
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Effo
rt (fi
sher
days
)
0
5
10
15
20
25
30
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
CPU
E (k
g/fis
herd
ays)
Coffin Bay
Fig. 3.8 Coffin Bay. Top graph - historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE by gear type.
31
Southern Spencer Gulf
Handlines have always been the dominant gear type in this region followed by hauling nets and
gillnets. The gillnet catches fell considerably in 2000 and have remained low, adding up to only a
few tonnes per year. The hauling net catch was always higher than the gillnet catch before
dropping to only a few hundred kg per year as a consequence of the netting closures that were
implemented in 2005. Consequently, now only the statistics associated with the handline fishery
provide a reasonable indication of the stock status.
Handline catch has been highly variable over the years with three obvious peaks, one in 1986, the
next in 1991 and the third in 1997 (Fig. 3.9). Since then, catches have decreased systematically
from 131,074 kg to only 57,383 kg in 2004 after which there has been a systematic recovery in the
handline catch to 72,517 kg in 2010. Handline effort was particularly variable in this region
between 1984 and 1993. From then until 2004 there was a systematic decline in handline effort
which fell by more than one half from 7,778 to 3,584 fisherydays. From 2004 onwards, effort has
stabilised and even marginally increased.
The estimates of CPUE for handlines between 1984 and 2010 have been highly variable (Fig. 3.9).
There was a period from 1984 to 1997 during which they increased from 12.1 to 19.4 kg.
fisherday-1, but over the following six years declined back to 14.8 kg.fisherday-1. They
subsequently rose again to 21.4 kg.fisherday-1 in 2007, but by 2010 had fallen again by 10% to 19.3
kg.fisherday-1.
32
0
20000
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CPU
E (k
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ays)
Southern Spencer Gulf
Fig. 3.9 Southern Spencer Gulf. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type.
33
Northern Spencer Gulf
Hauling nets have consistently been the dominant gear type for catching King George Whiting in
this region (Fig. 3.10). Hauling net catch was relatively high and variable until 1997 after which
there has been a downward trend until 2010. The lowest hauling net catch of 16,897 kg was taken
in 2010. Handline catch has also declined considerably since the relatively high catches of the
early 1990s, resulting in the lowest catches between 2008 and 2010. The decline in handline catch
from 1993 onwards is consistent with a decrease in fishing effort, particularly between 1994 and
2001, but also from 2007 to 2010. Gillnet catches have declined to minimal levels since 2000 and
involved less than five fishers, and so are not presented on Fig. 3.10.
CPUE in the handline sector has varied in several phases between 1984 and 2007, but has
nevertheless demonstrated a long-term increasing trend (Fig. 3.10). CPUE in 1984 was 10.4
kg.fisherday-1 and gradually increased to 21.0 kg.fisherday-1 in 2005. However, since then it has
fallen consistently back to 15.6 kg.fisherday-1 in 2010.
Both targeted and non-targeted hauling net catches have declined since 1992 (Fig. 3.11), reflecting
continual declines in both targeted and non-targeted effort since 1988. CPUE of targeted effort
has been relatively stable since 1995. Alternatively, CPUE of the ‘no specific target’ category has
nearly doubled from 7.8 kg.fisherday-1 in 2001 to 14.3 kg.fisherday-1 in 2010.
34
0
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CP
UE
(kg/
fishe
rday
s)
Northern Spencer Gulf
Fig. 3.10 Northern Spencer Gulf. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type.
35
0100002000030000400005000060000700008000090000
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35
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CP
UE
(kg/
fishe
rday
s)
Northern Spencer Gulf
Fig. 3.11 Northern Spencer Gulf. Top graph - historical trends in hauling net catch for each of the three effort categories. Middle graph - historical trends in hauling net effort for each of the three effort categories. Bottom graph - historical trends in CPUE for each of the three effort categories.
36
Gulf St. Vincent
Hauling nets, handlines and gillnets have each contributed substantially to the fishery for King
George Whiting in Gulf St. Vincent over the years (Fig. 3.12). Hauling net catch was quite
variable from 1984, reached a peak of 37,762 kg in 1998 after which it has declined to the low
level of only 8,751 kg in 2009. Handline catches were highest through the early and mid 1990’s
but since then have had a long-term systematic decline from 39,168 kg to only 9,347 kg that was
attained in 2005. Since then they have recovered marginally to 11,148 kg in 2010. The gillnet
catches were also relatively low through 2000-2002, increased in 2003, but then decreased to a
minimum level of 2,017 kg in 2006. They have also recovered marginally to 9,975 kg in 2010.
Handline effort was quite variable from 1984 until it peaked in 1992, after which it systematically
declined to 2005 (Fig. 3.12). It was relatively steady for a few years before declining again in 2010.
The peak in effort in 1992 was 3,787 fisherdays, which fell to 789 fisherdays in 2005. Gillnet
effort has also declined over the same period, particularly between 2001 and 2006.
CPUE in the handline fishery increased consistently from 1984, attaining a maximum of 14.7
kg.fisherday-1 in 2001 before decreasing annually between 2001 and 2005 (Fig. 3.12). It has
subsequently varied between 12 and 14 kg.fisherday-1. CPUE for gillnets increased to 26.2
kg.fisherday-1 in 1999, but then became highly variable due to the low levels of catch and effort.
Hauling net catch has decreased considerably since 1998 (Figs. 3.12 & 3.13), primarily reflecting a
significant decline in effort directed at ‘no specific targeted species’. The different categories of
CPUE in the hauling net sector have either remained steady or increased in recent years.
Although targeted catch and effort have been relatively low in Gulf St. Vincent, the CPUE has
increased through the years particularly from 2003 to 2007. CPUE for the untargeted effort types
have been relatively stable.
37
0
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40000
50000
60000
1984
1986
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Cat
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Handline
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0500
10001500200025003000350040004500
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Effo
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1015202530354045
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1990
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2004
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2010
CPU
E (k
g/fis
herd
ays)
Gulf St. Vincent
Fig. 3.12 Gulf St. Vincent. Top graph – historical trends in total catch by gear type. Middle graph – historical trends in total effort by gear type. Bottom graph – historical trends in CPUE by gear type.
38
0
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No specific target
Targeting other species
0
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1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
CPU
E (k
g/fis
herd
ays)
Gulf St. Vincent
Fig. 3.13 Gulf St. Vincent. Top graph – historical trends in hauling net catch for each of the three effort categories. Middle graph – historical trends in hauling net effort for each of the three effort categories. Bottom graph – historical trends in CPUE for each of the three effort categories.
39
Kangaroo Island
Handlines have been the main gear type in this region since 1984. Handline catches increased
from 25,026 kg in 1986 to a maximum of 47,880 kg in 1998, after which they declined
substantially to 27,337 kg in 2002 (Fig. 3.14). Since then, the annual catch has been relatively
consistent.
Handline effort increased substantially between 1988 and 1992, before declining systematically
over the following years (Fig. 3.14). From 1992 to 2008, handline effort fell from 3,887 fisherdays
to 1,666 fisherdays, the lowest yet recorded. Handline effort has increased marginally again to
1,964 fisherdays in 2010.
CPUE in the handline sector increased moderately through the years to a maximum of 15.5
kg.fisherday-1 in 1998 (Fig. 3.14). After that, it slowly declined to 13.7 kg.fisherday-1 in 2002, but
subsequently increased up to 17.4 kg.fisherday-1 in 2007, the highest ever recorded. CPUE has
decreased since then back to 13.6 kg.fisherday-1 in 2010, falling by 16.0% from 16.2 kg.fisherday-1
in 2009.
40
Kangaroo Island
0
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02468
101214161820
1984
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2004
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2008
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CPU
E (k
g/fis
herd
ays)
Fig. 3.14 Kangaroo Island. Top graph - historical trends in total catch by gear type. Middle graph - historical trends in total effort by gear type. Bottom graph - historical trends in CPUE by gear type.
41
3.4 Discussion
The commercial fishery statistics for King George Whiting were considered here at two spatial
scales, i.e. at the State-wide and regional scales. At the former scale, the statistics demonstrated
some strong trends that largely reflected significant changes in the structure of the fishery.
Between 1984 and 2007, the State-wide catch of King George Whiting dropped in several
considerable increments. These reflected substantial reductions in handline and gillnet catches
since 1999 and a gradual decline in hauling net catch since 1992. Such reductions are the
consequence of substantial falls in commercial fishing effort. Both targeted handline and gillnet
fishing effort have fallen considerably since 1992. It is more problematic to determine levels of
targeted hauling net effort, nevertheless since 1984 there has been a substantial reduction in the
number of net endorsements that has culminated in a decrease in the total number of hauling net
fishing days (Fowler 2005), suggesting the likelihood that targeted hauling net fishing effort on
King George Whiting has also declined. The State-wide estimates of CPUE for handlines and
gillnets have generally increased since 1984 but nevertheless demonstrated considerable declines
during the early 2000s. Since 2002, the State-wide estimates of handline and gillnet CPUE have
increased. The recovery for handline CPUE was quite slow but nevertheless the estimates reached
new maxima relatively recently, i.e. in 2007 and 2009.
The analysis of fishery statistics at the regional scale indicated that there have been long-term,
broad-scale significant reductions in net fishing, which influenced the data that could be presented
for the different regions. As such, most data presented here related to the handline fishery, with
data for the net sector only presented for NSG and GSV. In most regions, handline CPUE
decreased around the early 2000s, generally to minima in 2002. Since then they have gradually
increased again to the extent that the estimates from 2008 to 2010 were close to their maxima.
Overall, these results are indicative of consistent declines in fishable biomass across most regions
throughout the early 2000s, followed by considerable recoveries in most regions to 2010, to the
extent that relatively high levels of fishable biomass have been available in recent years. However,
there are several exceptions to this generalisation to consider. Firstly, in NSG, handline CPUE
continued to fall after 2005 as a consequence of both falling catches and falling effort. The results
from the hauling net sector demonstrated conflicting trends and so did not help to resolve the
stock status in this region. Also, in SSG handline CPUE fell by 10% after 2007, whilst there was
also a notable drop in CPUE for KI in 2010.
42
4. ANALYSIS OF THE RECREATIONAL FISHERY
4.1. Introduction
It is now well known that for particular types of marine fish species, recreational fishery catches
can contribute significantly to the total catches and fishing effort (Henry and Lyle 2003, Coleman
et al. 2004). As such, recreational fishery statistics should be taken into consideration when
determining the status of such fish stocks and for resolving resource allocation issues. To achieve
this requires obtaining robust estimates of recreational catch that can be compared over time, and
compared with estimates of catch from the commercial sector. In order to obtain such statistical
estimates of recreational catch and effort requires sampling methods that differ from the
comprehensive logbook system that is generally used for collection of commercial fishery statistics
(Jones 2009). As such, different survey methods have been developed for recreational fisheries
that include creel and telephone/diary survey methods.
In South Australia, there have been three, broad-scale, recreational fishery surveys. The first was a
creel survey that was done through the period of 1994-96 (McGlennon and Kinloch 1997). The
two subsequent ones were State-wide telephone/diary surveys that were done in 2000/01 (Henry
and Lyle 2003) and 2007/08 (Jones 2009). South Australia also supports a charter boat fishery as a
component of the recreational sector, which involves numerous licensed charter boat operators
whose commercial enterprises are based on taking recreational fishers fishing. Because of the
limited number of these operators it is possible to track their fishing activity through logbooks
(Knight 2009). This has been done since September 2005 when it became mandatory for charter
boat operators to submit a monthly log that details their fishing activity throughout the previous
month, including information on the spatial distribution of their catch and effort.
The objectives of this chapter are to provide a summary of the data available for the recreational
catch and effort for King George Whiting in South Australian coastal waters, as provided by the
three broad-scale recreational surveys, and to provide a summary of the logbook data from the
charter boat sector for the period from September 2005 to June 2010.
43
4.2 Materials and Methods
Creel Survey (1994-96)
This was a large-scale, two-year project that provided annual estimates of the catches of
recreational boat-fishers in the main fishing areas of SA (McGlennon and Kinloch 1997). The
geographic range of the survey covered the three geographic regions of Gulf St. Vincent, Spencer
Gulf and the West Coast. Each region was divided into a number of circuits of boat ramps that
were surveyed using the “bus-route” method. To achieve this, researchers travelled around a set
of boat ramps and waited at each ramp for a prescribed period, where the number of boat trailers
was counted to estimate fishing effort, and fishers returning to shore were interviewed to obtain
estimates of their catches. These data on recreational catch and effort were used to derive
estimates of State-wide total catch and effort (McGlennon and Kinloch 1997). The survey was
done for Gulf St. Vincent from April 1994 to March 1995 and for Spencer Gulf and the West
Coast from April 1995 to March 1996. The creel survey was confined to major public boat ramps
during daylight hours. It largely excluded Kangaroo Island and east of Victor Harbor due to the
time and travel costs. As such, the estimates of recreational catch and effort represented selected
subsets of the overall recreational totals.
National Recreational and Indigenous Fishing Survey (NRIFS) (2000/01)
This was a national recreational survey that was undertaken between May 2000 and April 2001 for
which the methods and results are described comprehensively by Henry and Lyle (2003) and Jones
and Doonan (2005). For each state including SA, there were two primary components to the
survey. The first was a telephone interview screening survey that was done through March and
April 2000. In SA, 4,422, randomly-chosen households were interviewed to determine
participation rates in recreational fishing and to provide demographic information about
recreational fishers and details of boat ownership. The second component was a diary/telephone
survey of numerous households (2,428 diarists) from across the State to record accurate
information on recreational effort and catch. The data from both components were expanded to
population-wide estimates for the State. Since the diarists involved in the second part of the
survey were selected randomly from across the State, the survey is thought to have presented a
more comprehensive census of the total recreational and indigenous catch than the creel survey of
1994-96. Also, the telephone and diary survey included catches from charter boats, which
accounted for 1.7% of the recreational fishing effort recorded. Furthermore, because this was a
national survey, the estimates of catch and effort included the data from inter-state visitors who
fished in South Australia during the survey period. Nevertheless, the results presented in this
report are from SA residents only, so that they are comparable to the results that are presented
from the survey done in 2007/08.
44
The survey structure was based on 26 marine fishing blocks (Fig. 4.1). Unfortunately not all of
these blocks aligned perfectly with the South Australian Marine Fishing Areas, but in general there
was reasonable similarity to allow for a comparison with the geographic regions that are normally
considered for King George Whiting in SA (c.f. Fig. 3.1). Therefore, for each region it was
possible to undertake comparisons of the recreational catch taken in 2000/01, with those from
both 1994/96 and 2007/08 as well as with the commercial data collected in 2000/01.
Fig. 4.1 Map of South Australia showing the boundaries of the different geographic blocks used in the National Recreational and Indigenous Fishing Survey (Henry and Lyle 2003).
To achieve the regional and temporal comparisons it was necessary to convert the estimated
numbers of fish captured in 2000/01 in the different regions to estimates of captured biomass.
To do this, the numbers were multiplied by the estimate weights of average-sized fish for each
region, as determined from the market sampling of the commercial catch that was done between
1995 and 1997 (Fowler and McGarvey 2000). This assumed that there was no change in the
average size of King George Whiting in the different regions between 1995-97 and 2000-01.
45
South Australian Recreational Fishing Survey (2007/08)
This third, large-scale study essentially used the same survey-based approach that was used in the
NRIFS of 2000/01. The specific description of methods and the comprehensive results are
presented in Jones (2009). The study involved a telephone interview screening survey of 7140
randomly-chosen households to determine participation rates and identify the demographics of
recreational fishers. After this, a 12-month telephone survey of 1310 households was undertaken
between November 2007 and October 2008 to monitor fishing catches and effort. At the same
time, a series of boat ramp creel surveys were done in order to determine the sizes and weights of
the fish by species captured by the recreational fishers. This meant that the regional estimates of
catch by numbers could be converted to catch by weight. The estimates of catch and effort from
the survey were then multiplied up to population level. The same regions and fishing blocks that
were used for the NRIFS were used here (Fig. 4.1). This survey was designed to provide up-to-
date annual estimates of the participation rates of South Australian residents in recreational
fishing, their fishing effort and their catches of key species, such as King George Whiting. Since
this was a State-based survey rather than part of a national one, it was restricted to South
Australian residents, and so regional estimates of catch and effort excluded contributions from
inter-state visitors.
4.3 Results
Creel Survey (1994-96)
Over the two years of the recreational creel survey, 631 sample-days were surveyed during which
3,513 interviews were conducted. Total annual fishing effort was estimated at 988,980 boat hours,
distributed over 200,000 boat trips. Of this total fishing effort it was estimated that 41% was
targeted at King George Whiting. The total harvest of all major species was estimated to be
3,770,256 fish, which included 1,154,662 (31% of total) King George Whiting.
Of the catch of King George Whiting, 98.8% were taken in six of the fishery regions for which
commercial fishery data are considered, i.e. Far West Coast (FWC), Mid-West Coast (MWC),
Coffin Bay (CB), Southern Spencer Gulf (SSG), Northern Spencer Gulf (NSG) and Gulf St.
Vincent (GSV) (Table 4.1). These data suggest that targeted recreational effort increased from
west to east, probably reflecting the trend in human population density, with GSV having the
highest recreational effort due to the influence of metropolitan Adelaide. Total catches also
increased from west to east, presumably reflecting geographic variation in fishing effort.
However, CPUE was variable among the regions, i.e. NSG, SSG and FWC had the highest catch
46
rates, while GSV and the MWC produced the lowest.
In GSV, the total recreational catch was almost comparable with that of the commercial fishery
(Table 4.1). Westwards from there, the contribution of the recreational sector to the total catch
declined. In NSG and SSG, the recreational component was greater than a third of the total, but
for the FWC and MWC the recreational harvest was less than one sixth of the total.
Table 4.1 Summary of results of catch and targeted effort on King George Whiting, based on the creel survey of the recreational boat fishery through 1994 –1996 (McGlennon and Kinloch 1997).
Region Total catch (t) Total catch (numbers)
Targeted effort (boat-days)
CPUE (no.boat-day-1)
CPUE (kg.boat-day-1)
% of total by rec fishery
FWC 21.1 94,039 4,537.1 20.7 4.65 15.8 MWC 5.8 35,466 3,871.3 9.2 1.50 14.9 CB 21.3 110,184 7,039.4 15.7 3.03 28.1 SSG 80.5 274,220 15,605.8 17.6 5.16 39.3 NSG 51.9 227,269 12,267.7 18.5 4.23 34.9 GSV 85.1 399,536 33,230.9 12.0 2.56 48.4 Total 265.7 1,140,714 76,552.2 34.2
National Recreational and Indigenous Fishing Survey (NRIFS)
The estimated State-wide recreational harvest of King George Whiting by the residents of SA in
2000/01 was 1,511,313 fish, with an estimated total weight of 381.5 tonnes (Table 4.2), which was
43.6% above the estimated State-wide harvest from the creel survey (c.f. Table 4.1). In 2000/01,
the major regional contributors were CB, SSG and (GSV + KI), whilst the more distant regions of
the WC and SE contributed least. For the survey period, the total estimated State-wide catch of
King George Whiting was 820 tonnes, of which the recreational component accounted for 46.5%
(Table 4.2).
The NRIFS estimated that there were 328,277 recreational fishers in the State of South Australia,
representing approximately 176,000 households that used a total of 38,713 boats for their
recreational fishing activities (Jones and Doonan 2005). Recreational fishers from all South
Australian waters, including inland waters and the Lakes and Coorong, engaged in an estimated
2,216,041 fishing events that occupied a total of 9,767,947 fishing hours. Of these totals, it is
estimated that there were 1,544,295 fishing events and 5,783,000 fishing hours undertaken in
marine waters for Marine Scalefish fish species.
For King George Whiting, the total fishing effort was estimated at 1,303,710 fishing hours, of
which 80.6% was specifically targeted at this species (Table 4.3). All regions involved a high
proportion of targeted fishing effort. The highest levels of effort were in the two gulfs, whilst the
SE and WC attracted the lowest levels of recreational fishing effort on King George Whiting.
47
Table 4.2. Summary of results from the National Recreational and Indigenous Fishing Survey for the catches of King George Whiting by South Australian residents in South Australia for the period of May 2000 – April 2001, compared with estimates of the commercial catch over the same time period.
Region Estimate of numbers caught
Average weight per fish
(g)
Estimated recreational
catch (tonnes)
Estimated commercial
catch (tonnes)
Total regional catch (tonnes)
Recreational % of total
(FWC + MWC) 168,050 233.01 39.2 138.6 177.8 22.0 CB 445,111 199.40 88.8 24.3 113.1 78.5 SSG 338,303 322.09 109.0 107.7 216.7 50.3 NSG 231,364 209.51 48.5 69.0 117.5 41.3 (GSV + KI) 315,219 289.26 91.2 98.8 190.0 48.0 SE 13,266 362.20 4.8 0.3 5.1 94.1 Total 1,511,313 381.5 438.7 820.0 46.5
South Australian Recreational Fishing Survey (2007/08)
From November 2007 to October 2008, the estimated number of King George Whiting captured
by South Australian residents was 1,797,148, of which 30.5% were released (Table 4.4). The
highest catches of King George Whiting in terms of numbers were taken from (GSV + KI), WC
and SSG. A moderate catch was taken from NSG, and a relatively minor catch was taken from
the SE region. The lowest release rate was recorded from SSG, whilst high release rates were
recorded for the WC and NSG. The total estimated recreational harvest in 2007/08 was 324.4 t,
compared to 330.1 t by the commercial sector (Table 4.5). SSG and (GSV + KI) accounted for the
major proportions of the recreational catch. The total catch of King George Whiting across both
sectors was 654.5 t, of which 49.6% was accounted for by the recreational sector. There was
considerable variation amongst regions in the proportional contribution of the two sectors. There was
a total of 1,206,926 recreational fishing hours of effort on King George Whiting of which 72.8% were
targeted, with the highest levels of targeted effort in (GSV + KI) and in SSG (Table 4.4).
48
Table 4.3 Summary of regional estimates in 2000/01 of harvest and catch by numbers, as well as targeted and non-targeted fishing effort by the recreational sector, as determined by the National Recreational and Indigenous Fishing Survey (Jones and Doonan 2005).
Region Harvest numbers
Released numbers
Total catch % released Targeted effort (hrs)
Non-target effort (hrs)
Total effort (hrs) % targeted
(FWC + MWC) 168,050 81,964 250,014 32.8 111,969 22,318 134,287 83.4 CB 445,111 139,327 584,438 23.8 174,165 43,486 217,651 80.0 SSG 338,303 41,115 379,417 10.8 247,579 42,012 289,591 85.5 NSG 231,364 211,793 443,158 47.8 201,309 45,680 246,989 81.5 (GSV + KI) 315,219 99,561 414,780 24.0 274,221 82,649 356,870 76.8 SE 13,266 5,324 18,589 28.6 41,333 16,988 58,322 70.9 Total 1,511,313 579,084 2,090,396 27.7 1,050,576 253,133 1,303,710 80.6
Table 4.4 Summary of regional estimates in 2007/08 of harvest and catch by numbers, as well as targeted and non-targeted fishing effort by the recreational sector, as determined by the South Australian Recreational Fishing Survey in 2007/08 (Jones 2009).
Region Harvest numbers
Released numbers
Total catch % released Targeted effort (hrs)
Non-target effort (hrs)
Total effort (hrs) % targeted
WC 298,568 185,811 484,380 38.4 181,308 47,499 228,807 79.2 SSG 385,034 102,117 487,151 21.0 253,684 81,798 335,481 75.6 NSG 135,563 81,773 217,336 37.6 110,447 49,048 159,495 69.2 (GSV + KI) 416,252 172,176 588,428 29.3 317,834 144,634 462,468 68.7 SE 13,266 6,191 19,853 31.2 15,920 4,755 20,675 77.0 Total 1,248,683 548,068 1,797,148 30.5 879,193 327,734 1,206,926 72.8
Table 4.5 Summary of information used to calculate the total weight per region of the catch of the recreational sector and the comparative estimates of catches for the commercial sector. Recreational data were for November 2007 to October 2008 and commercial data for the financial year of 2007/08 (i.e. July 2007 to June 2008).
Region Harvest numbers
Ave. wt per fish (g) Estimated recreational
catch (tonnes)
Estimated commercial
catch (tonnes)
Total catch (tonnes)
Recreational % of total
WC 298,569 214.4 64.0 142.7 206.7 31.0 SSG 385,034 291.1 112.1 74.5 186.6 60.1 NSG 135,563 227.8 30.9 39.5 70.4 43.9 GSV + KI 416,252 230.1 112.4 73.3 185.7 60.5 SE 13,662 355.8 5.0 0 5.0 100.0 Total 1,249,080 324.4 330.1 654.5 49.6
49
Regional comparison amongst survey estimates of recreational catch
The estimated regional totals from the three different surveys for the recreational catches of King
George Whiting by residents of SA were compared (Fig. 4.2). The differences amongst regions
were generally consistent across the three surveys, i.e. in general high recreational catches were
taken from SSG and (GSV + KI), moderate levels were taken from WC and NSG whilst low
catches were taken from the SE coast. There were no consistent trends with respect to any of the
surveys giving consistently higher or lower results. The most aberrant result was the high estimate
of catch from the WC in 2000/01, which was driven by a high estimated harvest from Coffin Bay
in that year.
Fig. 4.2 Comparison of the regional estimates of recreational harvest between the creel survey of 1994/96, the NRIFS of 2000/01 and the South Australian survey of 2008/08. Top graph shows regional harvest of King George Whiting in numbers, bottom graph shows regional harvest in tonnes.
Recreational Charter Boat Sector
Since September 2005/06, the licensed charter boat operators have been required to provide
monthly catch returns that document their fishing activity and catches. The reported totals, in
terms of numbers and weight, of King George Whiting harvested per year are indicated in Table
4.6. The relatively low number of fish for 2005/06 partly reflects the fact that data were not
Fishery region
Rec
reat
iona
l har
vest
(n
umbe
rs)
Rec
reat
iona
l har
vest
(to
nnes
)
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
WC SSG NSG GSV+KI SE
creel survey 1994/96NRIFS 2000/01SA survey 2007/08
0
20
40
60
80
100
120
140
WC SSG NSG GSV+KI SE
creel survey 1994/96NRIFS 2000/01SA survey 2007/08
Fishery region
Rec
reat
iona
l har
vest
(n
umbe
rs)
Rec
reat
iona
l har
vest
(to
nnes
)
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
WC SSG NSG GSV+KI SE
creel survey 1994/96NRIFS 2000/01SA survey 2007/08
0
20
40
60
80
100
120
140
WC SSG NSG GSV+KI SE
creel survey 1994/96NRIFS 2000/01SA survey 2007/08
50
recorded for July and August in that financial year. Also, the annual estimates of weight taken
prior to July 2007 are underestimates as, to that time, not all charter boat operators recorded the
total weights of their daily catches. This was rectified from July 2007 onwards with the
introduction of new forms. Despite these qualifications, the estimated total annual catches still
indicate that tens of tonnes of King George Whiting were harvested by South Australia’s charter
boat sector each year. The fish have primarily been taken from the waters of KI as well as from
SSG and GSV (Fig. 4.3). The remaining regions of NSG as well as the WC (including Coffin Bay)
have contributed only minimally to the charter boat catches of King George Whiting. The relative
significance of the different regions has been consistent from year to year.
Table 4.6 Estimates of numbers and weight of King George Whiting harvested by the recreational charter boat sector between 2005/05 and 2009/10. Note that estimates for 2005/06 were for the shortened period of September 2005 to June 2006.
Year Harvest numbers
Estimated charter boat
catch (tonnes)
2005/06 39,778 12.7 2006/07 48,412 17.2 2007/08 52,531 19.1 2008/09 54,563 19.7 2009/10 49,928 18.8
The catches of King George Whiting by the charter boat sector from each of the three regions
that consistently gave the highest catches (KI, SSG and GSV) (Fig. 4.3), were compared on a
monthly time frame to assess whether there was any seasonal variation. The trends for both GSV
and KI displayed clear seasonality with the catches highest during December, January, February,
March and April (Fig. 4.4), before declining to lower levels between May and September (Fig. 4.4).
The seasonality was evident but nevertheless less distinct for SSG.
51
Fig. 4.3 Comparison of the regional catches by the charter boat sector by weight and number of fish harvested for the years of 2005/06 to 2009/10. Note that data collection in 2005 commenced in September, as such data for 2005/06 were for 10 rather than 12 months.
Fig. 4.4 Comparison of the monthly charter boat catches from September 2005 to June 2010, for each of GSV, KI and SSG.
0
5000
10000
15000
20000
25000
2005/06 2006/07 2007/08 2008/09 2009/10
CB
FWC
GSV
KI
MWC
NSG
SSG
0
1000
2000
3000
4000
5000
6000
7000
8000
2005/06 2006/07 2007/08 2008/09 2009/10
CB
FWC
GSV
KI
MWC
NSG
SSG
Tota
l wt (
kg)
Tota
l num
bers
0
5000
10000
15000
20000
25000
2005/06 2006/07 2007/08 2008/09 2009/10
CB
FWC
GSV
KI
MWC
NSG
SSG
0
1000
2000
3000
4000
5000
6000
7000
8000
2005/06 2006/07 2007/08 2008/09 2009/10
CB
FWC
GSV
KI
MWC
NSG
SSG
Tota
l wt (
kg)
Tota
l num
bers
0
1000
2000
3000
4000
5000
6000
7000
8000
Jan July Jan July Jan July Jan July Jan
2006 2007 2008 2009 2010
0
1000
2000
3000
4000
5000
6000
7000
8000
Jan July Jan July Jan July Jan July Jan
Gulf St. Vincent
0
1000
2000
3000
4000
5000
6000
7000
8000
Tota
l num
bers
Jan July Jan July Jan July Jan July Jan
Kangaroo Island
Southern Spencer Gulf
0
1000
2000
3000
4000
5000
6000
7000
8000
Jan July Jan July Jan July Jan July JanJan July Jan July Jan July Jan July Jan
2006 2007 2008 2009 2010
0
1000
2000
3000
4000
5000
6000
7000
8000
Jan July Jan July Jan July Jan July Jan
Gulf St. Vincent
0
1000
2000
3000
4000
5000
6000
7000
8000
Jan July Jan July Jan July Jan July JanJan July Jan July Jan July Jan July Jan
Gulf St. Vincent
0
1000
2000
3000
4000
5000
6000
7000
8000
Tota
l num
bers
Jan July Jan July Jan July Jan July JanJan July Jan July Jan July Jan July Jan
Kangaroo Island
Southern Spencer Gulf
52
4.4 Discussion
One of the primary aims for undertaking recreational fishing surveys is to determine the trends
over time in recreational catch and effort. Understanding the influence of recreational catch and
effort on total catch and fishing mortality has consistently been one of the primary uncertainties in
managing this fishery (Fowler et al. 2008). The results from the three broad-scale recreational
surveys done in South Australia, i.e. in 1994/96, 2000/01 and 2007/08 provide a time-series to
look for trends. Firstly, the data from these surveys have indicated that over the past 20 years,
recreational fishery catches of King George Whiting have been taken from broadly throughout
South Australia’s coastal waters, particularly from GSV, KI and SSG. Nevertheless, the temporal
trends have proven somewhat surprising. The data indicated that there was a considerable
increase in the State-wide recreational catch between the 1990s and 2000/01. However, the
results from the third survey in 2007/08 then suggested that there had been a considerable drop in
the total State-wide recreational catch of King George Whiting. This result was unexpected as
anecdotal reports had suggested that the increase in recreational fishing effort observed between
the 1990s and 2000s had continued throughout the 2000s. However, in fact, the recorded drop in
catch actually corresponds with an estimated reduction by 25.7% in the number of South
Australian residents who undertook recreational fishing activity in 2007/08 relative to 2000/01
(Jones and Doonan 2005, Jones 2009). The reduction in fishery catch was most evident for the
WC and also for NSG. Alternatively, there was an increase in catch from (GSV + KI) between
2000/01 and 2007/08.
The comparison of regional catches between the recreational and commercial sectors for each
time period indicated that the recreational catches represent considerable proportions of the totals.
These varied regionally with the relative contribution to total catches by the recreational sector,
being lowest on the WC but particularly high in the two gulfs. This spatial difference is likely to
reflect higher recreational fishing effort in the two gulfs, which are more easily accessed by the
large number of recreational fishers who live in metropolitan Adelaide. However, the variation in
recreational catches over time also meant that there was considerable variation in their
proportional contribution to the total State-wide catches. The estimated contribution of the
recreational catch varied from 34.2% in the 1990s to 46.5% in 2000/01 and then to 50% in
2007/08. It should also be acknowledged that the latter two figures are under-estimates as they do
not include the contributions from inter-state fishers.
53
5. POPULATION STRUCTURE
5.1 Introduction
Populations of fish that are subjected to fishing pressure normally experience some degree of
truncation of their age and size distributions as a consequence of the removal of the larger, older
individuals by the fishery. This can have considerable population-level effects by influencing egg
production, and ultimately recruitment success (Longhurst 1998; Francis 2003, Berkeley et al.
2004). As such, population structure can be an important indicator of the status of a fishery.
Nevertheless, its assessment as an indicator depends on having a good understanding of how the
population structure naturally varies spatially as a consequence of the life history of the species.
The characteristics of the populations of King George Whiting throughout South Australia’s
coastal waters have been determined on several occasions, revealing a complex interaction
between population structure and life history. King George Whiting are not distributed evenly
with respect to size and age (Fowler 1998, Fowler et al. 2000a, Fowler and McGarvey 2000).
Fishing catches from throughout Gulf St. Vincent, northern Spencer Gulf and from the bays of
the West Coast of Eyre Peninsula generally involve small fish from the 3+ age class. Alternatively,
fish sampled from Investigator Strait along the northern coast of Kangaroo Island and from south
eastern Spencer Gulf represent much broader size and age ranges that consist of multiple year
classes of fish that are up to 20 years of age. The latter populations occur in deeper waters in
more exposed places.
Tag/recapture studies have revealed that the populations on the spawning grounds that involve
the larger, older King George Whiting are replenished by migration from the northern gulfs
(Fowler et al. 2002). Thus, fish movement constitutes an important obligative process that closes
the life history cycle between the nursery areas and spawning grounds. The older, larger fish
found in the deeper offshore places constitute the spawning populations (Fowler et al. 1999). As
such, spawning by this species does not occur generally throughout all of South Australia’s coastal
waters, but rather only occurs at particular locations or spawning grounds. Given that there is an
obvious geographic separation between the spawning grounds and nursery areas, the eggs and
larvae must be advected to the nursery areas. As such, it is likely that the larger, older fish in the
spawning populations make substantial contributions to egg production and therefore the age
structures of these populations may be important indicators of egg production.
54
The age structures of King George Whiting show evidence of strong and weak year classes. This
suggests that year class strength is a consequence of recruitment processes, with the rates showing
considerable inter-annual variability. Furthermore, similar strong year classes have been evident in
both Southern Spencer Gulf and Investigator Strait, indicating that environmental influences over
recruitment operate at a broad geographic spatial scale.
The studies on population structure of King George Whiting that were done between 1995 and
1998 identified both the spatial dispersion patterns with respect to size and age, as well as the
locations of the spawning grounds (Fowler et al. 1999, Fowler and McGarvey 2000, Fowler et al.
2002). Sampling done between 2001 and 2004 focussed on the age structures of the populations
on the spawning grounds, which may have been important indicators of egg production. In each
case, these two historic sampling programs depended on samples that were accessed from both
the commercial and recreational fishing sectors. In 2006, a new sampling protocol for King
George Whiting was initiated, i.e. a fish market-based sampling protocol for the commercial catch.
So far this focussed market-sampling has been done for King George Whiting throughout three
financial years, i.e. 2006/07, 2008/09 and 2009/10. The aim of this chapter is to present the
results from this sampling and to provide a qualitative comparison with data collected from the
similar regions in the past that have been published elsewhere (Fowler and McGarvey 2000,
Fowler et al. 2000a). This will determine whether there is evidence for recent truncation of the
population structure that is relatable to fishing pressure.
5.2 Materials and Methods
The market sampling was done at the SAFCOL fish market, generally once per week, where a
team of three researchers processed samples of King George Whiting prior to the morning
auction. Catches were selected from those available on the market floor to ensure as broad a
geographic coverage as possible. A two-stage sampling protocol was used in processing the
catches. First, a relatively large number of fish were measured to obtain size information for the
catch, from which a random sub-sample of fish was taken for further biological analysis. Back in
the laboratory, the latter fish were measured for total length (TL) and weighed individually, sexed
and the stage of reproductive development determined. They were then dissected for the removal
of the sagittae, i.e. the largest pair of otoliths, for ageing. For this, one otolith from each fish was
embedded in resin and sectioned using a diamond saw to produce a thin transverse section. This
was mounted on a glass microscope slide and its structure was interpreted using low power
microscopy by counting the opaque zones. Each count was then interpreted to provide an
estimate of fish age (Fowler and Short 1998). For each region, an age/length key was developed
to convert the sample proportions by length into proportions by age. In this way, population size
55
and age structures were produced for each region. For this work, the State’s coastal waters were
divided into a number of regions for which the population structure data were presented. In
general these regions corresponded to those that were considered for the analysis of both the
commercial and recreational fishery statistics (Figs. 3.1, 4.1), with the primary difference being the
division of the waters of Gulf St. Vincent, Investigator Strait and Kangaroo Island. Throughout
this broad region, the data were grouped and presented for three areas: Northern Gulf St. Vincent
(MPAs 34, 35 & 36); Kangaroo Island bays (MFA 42); and the remaining waters of Investigator
Strait and Kangaroo Island (MFAs 39, 40, 41, 44, 48 & 49).
5.3 Results
Far West Coast (MFAs 8, 9 &10)
Across the three years, >6,000 fish captured from the bays of the Far West Coast (FWC) were
measured (Fig. 5.1). The resulting size distributions were characterised by medium-sized fish that
were generally <40 cm TL, although with a few large fish between 40 and 52 cm TL. The modal
sizes were 32 – 34 cm TL. The age structures consisted of the 2+ to 5+ age classes and were
dominated by the 3+ age class in both 2006/07 and 2009/10, but by the 2+ age class in 2008/09.
The latter reflects that the sampling in 2008/09 was done largely in March and April 2009, prior to
the nominated birthday of 1st May. As such, it is unlikely that the nominal differences in age
structures between years reflected either population truncation or the recruitment of a particularly
strong year class in 2008/09.
Mid West Coast (MFAs 15, 16, 17, 18)
The sizes of King George Whiting captured from the bays of the Mid West Coast (MWC) have
generally been small, i.e. <34 cm TL. This remained the case for the three years sampled between
2006/07 and 2009/10 during which the fish were small and the modal sizes were either 30, 31, or
32 cm TL (Fig. 5.2). There were, however, incidental catches of big fish up to 58 cm TL taken
from these bays in each year. The age structures generally involved the 2+ to 4+ age classes and
were dominated by the 3+ age class that accounted for 90% or more of the catches. The
exception to this was in 2008/09 when the 2+ age class dominated, which again reflected the
timing of the sampling trips to this region in this year.
56
Fig. 5.1 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Far West Coast of Eyre Peninsula.
Fig. 5.2 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from the Mid West Coast of Eyre Peninsula.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
FWC – 2008/09n = 2300
FWC – 2009/10n = 2105
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
FWC – 2006/07n = 2031
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
FWC – 2008/09n = 2300
FWC – 2009/10n = 2105
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
FWC – 2006/07n = 2031
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
MWC – 2008/09n = 1445
MWC – 2009/10n = 1289
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
MWC – 2006/07n = 320
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 160
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
MWC – 2008/09n = 1445
MWC – 2009/10n = 1289
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
MWC – 2006/07n = 320
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
57
Coffin Bay (MFA 27)
Approximately 3,500 fish captured in Coffin Bay (CB) between 2006/07 and 2009/10 were
measured for development of size structures. The size structures were consistent between years,
being skewed to the right as they were dominated by small fish with decreasing numbers of larger
fish (Fig. 5.3). Only a few fish >40 cm TL were captured from this region. The age distributions
also were consistent from year to year being dominated by the 3+ age class that generally
accounted for >60% of the fish aged in each year. The 4+ age class accounted for the majority of
the remaining fish with an occasional 2+ and 5+ fish also captured.
Fig. 5.3 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Coffin Bay, southern Eyre Peninsula.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
CB – 2008/09n = 1476
CB – 2009/10n = 1304
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
CB – 2006/07n = 695
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
CB – 2008/09n = 1476
CB – 2009/10n = 1304
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
CB – 2006/07n = 695
58
Northern Spencer Gulf (MFAs 11, 19, 20, 21, 22, 23)
Approximately 14,000 fish captured in Northern Spencer Gulf (NSG) between 2006/07 and
2009/10 were measured for development of size structures. The resulting size structures were
consistent between years, being skewed to the right as they were dominated by small fish with
decreasing numbers of larger fish (Fig. 5.4). Relatively few fish >40 cm TL were captured from
this region. The age distributions also were consistent from year to year being dominated by the
3+ age class that generally accounted for >70% of the fish aged in each year. The 2+ and 4+ age
classes accounted for the majority of the remaining fish with an occasional fish from the 5+ and
6+ age classes also captured.
Fig. 5.4 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Northern Spencer Gulf.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
NSG – 2008/09n = 5710
NSG – 2009/10n = 3774
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
NSG – 2006/07n = 4494
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 160
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
NSG – 2008/09n = 5710
NSG – 2009/10n = 3774
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
NSG – 2006/07n = 4494
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
59
Southern Spencer Gulf (29, 30, 31, 32, 33)
Greater than 9,000 fish captured in Southern Spencer Gulf were measured. Although the size
distributions were again skewed to the right, due to the small and decreasing numbers in the larger
size classes up to 52 cm TL, the fish were generally larger than those captured in NSG (Fig. 5.5).
The modal sizes were between 35 and 37 cm TL in the three years. The age distributions were
relatively consistent between years and were dominated by the 3+ and 4+ age classes.
Furthermore, there were relatively more fish in the older age classes, i.e. up to the 13+ age class
than were recorded for NSG or either the FWC or MWC.
Fig. 5.5 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Southern Spencer Gulf.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SSG – 2008/09n = 4040
SSG – 2009/10n = 1310
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
SSG – 2006/07n = 3719
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SSG – 2008/09n = 4040
SSG – 2009/10n = 1310
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt
SSG – 2006/07n = 3719
60
Gulf St Vincent (MFAs 34, 35, 36)
Almost 7,000 fish were sampled from northern Gulf St. Vincent, primarily from MFAs 34 & 35.
The resulting annual size distributions primarily involved small-medium fish, i.e. <40 cm TL, with
a small number of fish up to 52 cm TL also captured (Fig. 5.6). The modal sizes varied between
33 and 35 cm TL across the three years. The age structures were consistently dominated by the
3+ age class whilst the remaining fish were largely from the 2+ and 4+ age classes, although with
occasional representation from the 5+, 6+ and 7+ age classes.
Fig. 5.6 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Gulf St. Vincent.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
GSV – 2008/09n = 2816
GSV – 2009/10n = 2444
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt GSV – 2006/07
n = 1407
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
GSV – 2008/09n = 2816
GSV – 2009/10n = 2444
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt GSV – 2006/07
n = 1407
61
Kangaroo Island (MFA 42)
MFA 42 (refer Fig. 3.1) was considered independently from the other MFAs in this region because
it includes the inshore, shallow bays of Kangaroo Island, which have traditionally provided large
numbers of relatively small King George Whiting to the local fishery, probably reflecting that its
coastal margins constitute an important nursery area. Nevertheless, the fish sampled from this
MFA between 2006/07 and 2009/10 reflected relatively complex size structures (Fig. 5.7). Those
for 2006/07 and 2008/09 reflected the influence of several modes of small and relatively large
fish. This probably relates to the small fish being captured in the bays in relatively shallow water
whilst the larger ones were captured further offshore. Each size distribution is skewed to the right
and includes relatively high contributions from fish in the high 30’s and 40’s cm TL. The age
structures were also relatively complex. Although dominated by the 3+ age class they nevertheless
involve considerable numbers of 4+ and 5+ fish and small contributions from the 6+ and 7+ age
classes.
Fig. 5.7 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from MFA 42 in Investigator Strait.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
KI – MFA 42 2008/09n = 1255
KI – MFA 422009/10n = 1640
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt KI – MFA 42
2006/07n = 528
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
KI – MFA 42 2008/09n = 1255
KI – MFA 422009/10n = 1640
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt KI – MFA 42
2006/07n = 528
62
Kangaroo Island / Investigator Strait (MFAs 39, 40, 41, 43, 44, 48, 49)
Although the remaining area of southern Gulf St. Vincent, Investigator Strait and around
Kangaroo Island included numerous MFAs, the samples considered for this region primarily came
from MFAs 40 & 41 (Fig. 3.1). Only 1,374 fish, i.e. a relatively low number, were measured from
across the three years, from which the size structures were developed. The annual size
distributions tended to be broader than for the other regions as they demonstrated higher
proportional contributions of the 40 – 50 cm TL size classes (Fig. 5.8). Nevertheless, relatively
small fish were still represented with the modal sizes being 35 or 36 cm TL in each year. The age
structures were also complicated and skewed to the right, indicating decreasing contributions up to
the 16+ age class. Nevertheless, the 3+ and 4+ age classes dominated numerically.
Fig. 5.8 Age and size structures of samples of King George Whiting collected in 2006/07, 2008/09 and 2009/10 from Kangaroo Island / Investigator Strait.
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
KI – IS 2008/09n = 555
KI – IS2009/10n = 405
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt KI – IS
2006/07n = 414
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0
5
10
15
20
25
30
35
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 600
10
20
30
40
50
60
70
80
90
100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
KI – IS 2008/09n = 555
KI – IS2009/10n = 405
Per
cent
TL (cm) Age (yr)
Per
cent
P
erce
nt KI – IS
2006/07n = 414
63
5.4 Discussion
Earlier sampling-based studies have documented the size and age structures of populations of
King George Whiting captured from throughout South Australia’s coastal waters and have
consistently demonstrated that there are considerable differences in population structure at
different locations. Furthermore, these differences relate to the reproductive biology of the
species that result in a complex relationship between habitat, population structure and
reproductive maturity and activity (Fowler et al. 2000a). Fish located in shallow inshore areas
adjacent to nursery areas tend to be relatively small young and immature. Alternatively, fish
located in deeper water associated with off-shore reefs, shoals or large mounds in exposed
locations that experience medium to high wave energy tend to have more extensive size and age
structures. Furthermore, these are the places where reproductive maturation takes place, and
thereby represent the spawning grounds. Such populations can involve fish up to approximately
20 years of age, which means that in any year there are numerous age classes in the populations.
The intention of considering the data on population structure in a fishery context is to determine
whether there is evidence of a reduction in the number of age or size classes in the population as a
consequence of the fishing activity. This occurs because fishing tends to remove the largest,
oldest individuals from the fish population and thereby reduces the number of age classes in the
population (Berkeley et al. 2004).
Since age-based sampling commenced in the 1990s in a number of the regions considered here, i.e.
the FWC, MWC, NSG and GSV the populations have been characterised by relatively small,
young fish that have been primarily dominated by the 3+ year class (Fowler and McGarvey 2000,
Fowler et al. 2000a, Fowler et al. 2005). Such fish recruit to the fishery as fast-growing 2+ or as
3+ fish. They are fished relatively heavily in this gauntlet fishery, whilst their numbers are also
depleted as the fish emigrate southwards in the gulfs or leave the bays of the west coast (Fowler et
al. 2002). Since these populations primarily consist of a single year class, it would be difficult to
detect truncation of their age structures. In fact, in contrast there are some indications that older
fish in the 5+ and 6+ year classes are now being captured more often in these northern regions.
The fish that emigrate as 3+ individuals from the northern gulfs move to the spawning
populations that are located in the deeper waters of SGSV, SSG or Investigator Strait that support
multiple age classes of up to 20 years of age (Fowler et al. 2002). So far, the size and age
structures of these populations have been monitored through several programs from 1996 to
1998, from 2001 to 2004 and most recently from 2006/07 to 2009/10. In comparing the results
between sampling regimes during these periods for the different regions it is apparent that the age
64
structures still support relatively old fish. SSG still has some fish that are up to 13 years of age and
Investigator Strait supports fish that are up to 16 years of age, whilst the 6+ to 10+ age classes
have consistently been relatively abundant in the fishery catches over time. Overall, these results
provide no evidence of any reduction in the size or age structures of these populations of King
George Whiting between the 1990s and 2000s that can be related to fishing activity.
65
6. MODEL ASSESSMENT OF BIOLOGICAL PERFORMANCE INDICATORS
6.1. Introduction
WhitEst model: description and input data
For King George Whiting in South Australia the primary management objective remains to ensure
sustainability of the fishery. To facilitate this, a computer fishery model was developed in an
FRDC-funded project (Fowler and McGarvey 2000). This is a dynamic, spatial, age- and length-
structured model that is used to integrate data from the most recent complete calendar year to
provide estimates of biological performance indicators on the status of the fishery. The model
divides the fishery into six spatial cells, five of which contribute most of the catch, i.e. the West
Coast, and the northern and southern regions of the two gulfs, whilst the last cell is located
offshore from the West Coast (Fig. 6.1). The model quantifies rates of yearly summer migration
from inshore nursery areas in the northern gulfs to the spawning regions in the southern gulfs.
Exploitation rates are high in the upper gulfs and inshore, but lower in the southern-gulf offshore
spawning grounds. A spatial breakdown with a monthly time step allows the model to account for
seasonal movement and exploitation levels that vary seasonally and in space. The data sources
informing maximum likelihood estimation of model parameters are (1) monthly catch and effort
totals, (2) samples of the commercial catch giving proportions by age and sex in different spatial
cells for most months through the three sampling periods of September 1994-June 1997 and July
2004-June 2007, and July 2008-December 2010, (3) information on King George Whiting
movement in the two South Australian gulfs from tag/recapture studies undertaken in the 1960’s,
1970’s, and 1980’s. Migration rates from northern to southern gulf regions are estimated
(McGarvey and Feenstra 2002) with other parameters in the overall model likelihood. WhitEst
uses a partition of model fish numbers by length in each age group, dividing the gaussian length
distribution of each yearly cohort into length bins called ‘slices’. A new slice of fish is created in
each monthly time step, a ‘slice’ being defined as the fish that grow into legal size each month.
Growth, as mean estimated length-at-age and the standard deviation of lengths about each
monthly age, was estimated from age-length samples (McGarvey and Fowler 2002) and used as
input to the slice partition submodel. This slice partition model framework (McGarvey et al. 2007)
quantifies the on-going monthly growth of each cohort into the legally harvestable size range, with
faster growth observed during the months of warmer water temperatures in late summer and
autumn of each year. The arrival of each cohort to legal size attracts a large shift of MSF fishing
effort to newly legal-size King George Whiting each winter, with commercial effort often peaking
in July. The slice partition method separates these heavily exploited legal-size fish from sublegal
fish, and keeps account of the dynamically changing numbers of legal fish by both age and length.
66
The model is fitted to monthly catches, conditional upon the effort in fisher days required to take
each catch. Catch and effort data are analysed and modelled separately for the four gear types
(handline, hauling net, gillnet, and all other gears combined) and three target types (targeting King
George Whiting, targeting any other specific marine scalefish species, and not targeting any species
in particular) reported in monthly commercial catch and effort logbooks. Recreational catch and
effort by month and spatial cell are from the two most recent surveys (2000/01 and 2007/08;
Chapter 4) which each covered one year of monthly catches. Further details of WhitEst are
included in the FRDC final report (Fowler and McGarvey 2000). The King George Whiting
model was externally reviewed by Dr André Punt (University of Washington, Seattle, USA).
Fig. 6.1 Map of South Australia showing the Marine Fishing Areas in which commercial catch and effort are reported, and the 6 spatial cells used in WhitEst, the King George Whiting stock assessment model.
67
WhitEst model indicators: recruitment, biomass and exploitation rate
The model outputs three principal biological performance indicators: recruitment, legal-size
population biomass, and exploitation rate. Biomass and exploitation rate are given as monthly
model estimates, and also as yearly averages. Yearly biomass is computed as the mean of monthly
model-estimated biomass levels for each calendar year. Exploitation rate (also known as harvest
fraction) is the fraction of biomass harvested yearly. For King George Whiting, the yearly
exploitation rate performance indicator is calculated as the sum of monthly model catches across
all gear and target types in each calendar year divided by the (yearly average) legal biomass.
Recruitment is estimated in the model as the yearly number of 1 year olds, but this is best
understood as a relative measure of recruits to legal size since only legal-size recruits are reported
in the commercial catch and effort data sets upon which these estimates are based. In the
recruitment time series graphs, the year shown on the x-axis is the year each cohort has fully
entered the fishable stock and is principally targeted in the fishery as 3 year olds.
6.2 Results
WhitEst model biological performance indicators are presented in three figures (Figs. 6.2-6.4).
The seasonal (monthly) variation in biomass and exploitation rate by the two sectors is shown for
the three main South Australian fishery regions in Fig. 6.2. State-wide aggregated yearly estimates
for the three King George Whiting biological performance indicators of recruitment, legal-size
biomass, and exploitation rate are plotted, with confidence intervals, in Fig. 6.3. These same yearly
performance indicators are shown broken down for the three fishery regions (Gulf St. Vincent,
Spencer Gulf and West Coast) in Fig. 6.4. In what follows below, specific stock assessment
observations, based on the model results plotted in these figures, are summarised.
1. Seasonal variation: Consistent with strong seasonal variation in monthly catch and effort (Fig.
3.5), monthly model biomass (Fig. 6.2, pink plotted lines) and commercial exploitation rates
(Fig. 6.2, blue plotted lines) show steady seasonal trends in the two gulfs and the West Coast
(Fig. 6.2). The yearly cycle of commercial exploitation lags several months behind the yearly
cycling trend in biomass. King George Whiting are most abundant in autumn and winter
subsequent to the late summer and early autumn season of fastest growth when each age-3
cohort predominantly recruits to harvestable size. Seasonal peaks in commercial catch occur
in mid-winter (Fig. 3.5), when the effort of fishers is principally targeted on this newly
recruited year class of 3-year-olds. The model estimates a catchability for age-3 fish to be
more than twice that of other age groups, consistent with this description of seasonal variation
in the South Australian King George Whiting fishery, whereby commercial effort ramps up
68
each winter to target the enhanced biomass of the newly recruited age-3 cohort. Recreational
exploitation (Fig. 6.2, green plotted lines) is also seasonal, with spikes evident in the months of
school holidays.
2. Long-term trends, biomass and recruitment: Since model catch and effort data were first
collected in July 1983, yearly model population abundance indicators for South Australian
King George Whiting have been generally stable. Over decadal time scales, the trends of
State-wide model estimates of recruitment (Fig. 6.3a) and biomass (Fig. 6.3b) have shown
relatively flat time trends with modest yearly variation. In the last 6 years, State-wide
recruitment and biomass have stabilised at levels modestly higher than average. This very
stable and modestly higher stock abundance in recent years, notably since heightened
management controls were implemented in 2004 (Section 2.3), suggests an exploited fish
population in generally good health.
3. Long-term trends, exploitation rate: State-wide model-estimated exploitation rate has shown a
steady decline over two decades (Fig. 6.3c). This reflects the declining trend in the number of
M- and B-class Marine Scalefish licence holders who catch and target King George Whiting
(Fig. 3.4). Recreational exploitation also declined over the time between the two more
comparable recreational surveys used in the model (2000/01 to 2007/08; comparing Tables
4.3 with 4.4). Over the last four years, overall exploitation rate (both sectors combined; Fig.
6.3c) has been unchanged at an all-time low level.
4. Recent years (2008-2010), biomass and recruitment: The one notable feature of the last three
years is the 1-year increase observed in 2009 for both recruitment and legal-size biomass (Fig.
6.3). Comparing the recruitment trends for the three regions (Fig. 6.4), it is evident that this
increase was observed principally in the West Coast fishery, where handline CPUE in 2009
was the highest on record for both the Far West Coast (Fig. 3.6) and the Mid West Coast (Fig.
3.7). The factors, presumably environmental, which permitted higher recruitment of the King
George Whiting cohort that recruited as 3-year olds in 2009 (2006 year class) along the South
Australian West Coast are unknown.
5. The addition of a second recreational survey in 2007/08 improved knowledge for longer-term
trends in overall King George Whiting exploitation rates. This uncertainty was not fully
resolved since out-of-state fishers could not be included in this specifically South Australian
telephone and diary recreational survey. Model data inputs continue to come principally from
the commercial sector with recreational catch estimated to comprise about half the total State-
wide catch in 2007/08. In the absence of detailed time series data for the recreational sector,
69
the WhitEst model assumes that recreational catch and effort varied in proportion with the
South Australian human population prior to 2000/01, declined linearly between survey-
estimated values from 2000/01 to 2007/08, and was flat at 2007/08 survey levels thereafter.
The omission of out-of-state recreational catch and effort was ignored.
70
Bio
mas
s (to
nnes
)
500
1000
1500
2000
2500
3000
3500
Exp
loita
tion
rate
0.00
0.01
0.02
0.03
Biomass (tonnes)Comm Expl Rate Rec Expl Rate
Bio
mas
s (to
nnes
)
800
1000
1200
1400
1600
1800
Exp
loita
tion
rate
0.00
0.01
0.02
0.03
0.04
0.05
0.06
Model time step (months)
01-J
an-0
1
01-J
an-0
2
01-J
an-0
3
01-J
an-0
4
01-J
an-0
5
01-J
an-0
6
01-J
an-0
7
01-J
an-0
8
01-J
an-0
9
01-J
an-1
0
01-J
an-1
1
Bio
mas
s (to
nnes
)
500
550
600
650
700
750
Exp
loita
tion
rate
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
(a) West Coast
(b) Spencer Gulf
(c) Gulf St. Vincent
Fig. 6.2 Seasonal variation in biomass and exploitation rate by the recreational and commercial sectors, 2001-2010, for the South Australian King George Whiting population. Monthly WhitEst model-estimated performance indicators of legal biomass, and exploitation rate broken down by sector, are plotted for each of the three main fishery regions.
71
Year cohort reaches fishable stock (age 3)
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 20090
10
20
30
40
50(a) Recruitment (millions)
0
1000
2000
3000
4000
5000
6000
Calender year
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 20090.0
0.1
0.2
0.3
0.4
0.5
(b) Yearly legal biomass (tonnes)
(c) Yearly exploitation rate
Fig. 6.3 Yearly State-wide (excluding spatial cell 6) model biological indicators 1984-2010 for South Australian King George Whiting. These performance indicators of (a) yearly recruit numbers, (b) legal biomass averaged over the 12 months of each calendar year, and (c) harvest fraction as the yearly model-estimated catch divided by the yearly average legal biomass, are estimated by the FRDC-sponsored spatial dynamic stock assessment model (WhitEst). Error bars show 95% model estimate confidence intervals.
72
(a) Recruitment (millions)
(b) Full year average legal biomass (tonnes)
(c) Yearly exploitation rate
Year cohort reaches fishable stock (age 3)
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 20090
10
20
30
40 West CoastSpencer GulfGulf St. Vincent
0
500
1000
1500
2000
2500
3000
3500
Calender year
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 20090.0
0.1
0.2
0.3
0.4
0.5
(a) Recruitment (millions)
(b) Yearly legal biomass (tonnes)
(c) Yearly exploitation rate
Fig. 6.4 Regional yearly model biological indicators 1984-2010 for South Australian King George Whiting. Regions are the West Coast (including Far and Mid West Coast, and Coffin Bay, spatial cell 1 shown in Fig. 6.1), Spencer Gulf (spatial cells 2 and 3), and Gulf St. Vincent and Kangaroo Island (spatial cells 4 and 5). Error bars show 95% confidence intervals.
73
7. ASSESSMENT OF FISHERY PERFORMANCE INDICATORS
7.1 Introduction
The Management Plan for the Marine Scalefish Fishery of South Australia provides a strategic
framework to guide fishery management decisions (Noell et al. 2006). This framework links the
management goals with the stock assessment process and also identifies the appropriate responses
to the potential outcomes of the assessment. Essential to this process are fishery performance
indicators that relate to the status of the fishery with respect to the management objectives. For
this fishery there are two sets of fishery performance indicators that are assessed against particular
limit reference points. These are the ‘general performance indicators’ that relate to the commercial
catch and effort data and ‘biological performance indicators’ that relate to estimates of biological
parameters. For the former, the indicators and reference points that are specified in the
Management Plan (Noell et al. 2006) were not used in this assessment. At a meeting of the Marine
Scalefish Fishery Management Committee that was held on the 17th February 2006 it was agreed
that new sets of general performance indicators and limit reference points should be adopted
(Minutes of meeting No. 98 of MSFMC), which are outlined below. The biological performance
indicators remain as specified in the Management Plan (Noell et al. 2006).
7.2 Materials and Methods
General Performance Indicators
Here only the commercial fishery statistics for the handline gear type were considered. Because of
the considerable declines in fishing effort with nets it is now likely that the fishery statistics from
those gear types do not provide good indicators of fishable biomass. Three general fishery
performance indicators were calculated from the commercial handline statistics; total commercial
catch, targeted effort, and targeted CPUE. These were assessed against the following limit
reference points:
1. the 3rd highest and 3rd lowest values over the reference period;
2. the greatest (%) inter-annual variation (+ and -) over the reference period;
3. the greatest rate of change (trend) over periods of three years (+ and -) through the
reference period.
Since commercial catch and effort data from a further three years were presented in this report, i.e.
for 2008, 2009 and 2010 (Chapter 3), the status of the fishery at the State-wide scale at the end of
74
each year was considered. As such, the annual State-wide totals of commercial catch, effort and
CPUE for the handline sector were calculated for each calendar year from 1984 until each
prescribed year. In each case, the limit reference points were then derived based on that time-
series of data. The estimates of data in each of 2008, 2009 or 2010 were then compared with the
limit reference points determined for the whole appropriate time series.
The general fishery performance indicators were also considered at the regional scale, using the
same method as described above. Here only the handline data from 2010 for each of the seven
fishery regions were considered.
Biological Performance Indicators
The four biological performance indicators that were assessed for King George Whiting were
fishable biomass, recruit numbers, exploitation rate of the fishable biomass, and age structure
(Noell et al. 2006). The first three were outputs from the WhitEst model (Chapter 6), and the
fourth relates to the analysis of population structure that was presented in Chapter 5.
The definitions of the population time-series indicators for biomass, recruitment, and exploitation
rate, as estimated by WhitEst, were the same as used in Fowler et al. (2008). Yearly biomass was
calculated as the average of monthly model estimates. Recruits, computed as model estimates of
1-year old fish numbers for each cohort, are inferred entirely from observed legal-size recruits in
commercial catch age-length samples and catch rates, and so constitute a measure of recruitment
to legal size. Yearly exploitation rate was calculated as the ratio of the model-estimated catch
summed over the whole year, divided by the yearly average biomass, as defined above. Using
model rather than data catch for computing exploitation rate is appropriate because it is consistent
with mortality rate inferred from age samples that underlie the best estimates of exploitation rate.
For fishable biomass and recruits, the corresponding limit reference points were triggered if the
indicator in the most recent (reference) calendar year was either 10% lower or greater than its
average over the previous five years (Noell et al. 2006). For fishable biomass, the WhitEst model
estimates for 2010 were compared with the yearly time averages from 2005 to 2009. For
recruitment, the 2009 3-year-olds were compared with the model-estimated yearly time averages
from 2004 to 2008. Estimates of all three biological performance indicators were evaluated for the
State overall (Fig. 6.3), and for each of the three main regions considered in the WhitEst model,
i.e. West Coast, Spencer Gulf and Gulf St. Vincent (Fig. 6.4). The overall (State-wide) indicators
of biomass and recruitment were summed across the three regions (but excluding the outlying
75
regions of cell 6, see Fig. 6.1), while exploitation rate for each calendar year was computed as the
ratio of yearly model catch divided by the yearly biomass within each region.
7.3 Results
General Performance Indicators
For the assessment of the general performance indicators up to the end of each of 2008, 2009 and
2010, several limit reference points were breached (Table 7.1). In 2008, the 2nd lowest
commercial handline catch was recorded whilst in 2010 the 3rd lowest catch was recorded. Also,
the highest ever catch rate was recorded in 2009.
Table 7.1 Summary of the results of the comparisons between general and biological fishery performance indicators and the limit reference points for the King George Whiting fishery, based on State-wide data. Performance Indicator Limit Reference Point Year Breached ? Details Total commercial catch 3rd lowest/ 3rd highest 2008 Yes 2nd lowest
2009 No 2010 Yes 3rd lowest
Greatest inter-annual change 2008 No 2009 No
2010 No Greatest 3-year trend 2008 No 2009 No
2010 No Total commercial effort 3rd highest 2008 No
2009 No 2010 No
Greatest inter-annual change 2008 No 2009 No
2010 No Greatest 3-year trend 2008 No 2009 No
2010 No Target handline CPUE 3rd lowest/ 3rd highest 2008 No
2009 Yes Highest 2010 No
Greatest inter-annual change 2008 No 2009 No
2010 No Greatest 3-year trend 2008 No 2009 No
2010 No
76
With respect to the consideration of general fishery performance indicators at the regional scale
for the data from 2010, there were several breaches of limit reference points. For each of the
FWC, NSG, GSV and KI the lowest or near lowest handline catches after 1984 were recorded in
2010 (Tables 7.2, 7.6, 7.7, 7.8). Simultaneously, high catch rates were recorded for the MWC and
CB (Tables 7.3, 7.4). Alternatively, the decline in catch rate observed for KI in 2010 breached
several limit reference points (Table 7.8).
Table 7.2 Comparisons between general performance indicators for 2010 and limit reference points for FWC.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest Yes 3rd Highest
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Table 7.3 Comparisons between general performance indicators for 2010 and limit reference points for MWC.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest Yes 3rd Highest
Greatest interannual change (+) No Greatest 3-year trend No
Table 7.4 Comparisons between general performance indicators for 2010 and limit reference points for CB.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest Yes 3rd Highest
Greatest interannual change (+) No Greatest 3-year trend No
77
Table 7.5 Comparisons between general performance indicators for 2010 and limit reference points for SSG.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Table 7.6 Comparisons between general performance indicators for 2010 and limit reference points for NSG.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest Yes Lowest
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Table 7.7 Comparisons between general performance indicators for 2010 and limit reference points for the GSV.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest Yes 3rd lowest
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Table 7.8 Comparisons between general performance indicators for 2010 and limit reference points for KI.
Performance Indicator Limit Reference Point Breached ? Details Handline catch 3rd lowest/3rd highest Yes 3rd lowest
Greatest interannual change (+) No Greatest 3-year trend No
Handline effort 3rd highest No
Greatest interannual change (+) No Greatest 3-year trend No
Handline CPUE 3rd lowest/3rd highest No
Greatest interannual change (+) Yes Greatest 3-year trend Yes
78
Biological Performance Indicators
The biological performance indicators (BPI) for South Australian King George whiting (Table 7.9)
were generally positive. None of the biomass BPI’s triggered, as estimates of biomass in 2010
were all close to the previous 5-year averages, which were slightly higher than previous years (Fig.
6.3 and 6.4). One recruitment BPI triggered for Spencer Gulf signalled the recruitment of a lower
year class to this region in 2010. Nevertheless, this single lower year of recruitment would not
suggest a trend of lower abundance, with the previous 5-year recruitment average in Spencer Gulf
pulled upward by a strong 2005 cohort (Fig. 6.4a).
The one BPI breach of concern is of 30% exploitation rate in Gulf St. Vincent. In strong contrast
to the two other major regions, exploitation rate in Gulf St. Vincent has remained relatively high
and has trended higher in the last three years (Fig. 6.4). The breakdown of Gulf St. Vincent
exploitation rate between the two sectors (Fig. 6.2c), and the comparison of the two most recent
recreational surveys (Tables 4.3 and 4.4, (GSV+KI)) suggests that recreational exploitation rate of
King George whiting rose substantially in this gulf between 2000/01 and 2007/08. There has
been no apparent change in population age structures over the past five years.
Table 7.9 Yearly biological performance indicators considered in the WhitEst model, for the three regions, and for the State overall. Limit reference points that have been breached are highlighted in yellow. The current performance year covers the period January 2010 – December 2010.
Biological performance indicator
Biological limit reference point
West Coast Spencer Gulf Gulf St. Vincent State-wide
Fishable Biomass
Ref year +/- 10% of previous 5-yr average
2010 biomass 3% above average of
previous 5 years
2010 biomass 1% below average of
previous 5 years
2010 biomass 2% below average of
previous 5 years
2010 biomass 1% above average of
previous 5 years
Recruitment
Ref year +/- 10% of previous 5-yr average
2007 year class 1.8% above average of previous 5 years
2007 year class 18% below average of
previous 5 years
2007 year class 4% below average of
previous 5 years
2007 year class 2.5% below average of previous 5 years
Exploitation rate
Exceeds international standard (28% yearly)
10% 20% 30% 17%
Age structure
Significant change over previous 5 years
No change over time
No change over time
No change over time
No change over time
79
7.4 Discussion
There were relatively few breaches of the limit reference points for the general fishery indicators,
which generally related to the relatively low catches of King George Whiting in 2010 at both the
regional and State-wide scales. These reflect the declining fishing effort rather than a reduction in
the catch rate. Only for KI, did rather dramatic declines in catch rate in 2010 trigger several limit
reference points.
Similarly, for the biological performance indicators there were few breaches of limit reference
points. For the first time, the exploitation rate for GSV, which was estimated by WhitEst to be
30%, exceeded the international standard of 28%. Commercial fishing effort has been relatively
stable in this region for a number of years, whereas the results from the recreational surveys in
2000/01 and 2007/08 indicate that recreational catch and effort did increase in this region
throughout the 2000s.
80
8. DISCUSSION
8.1 Context of this assessment
In the early 2000s there was considerable concern about the long-term sustainability of the South
Australian King George Whiting fishery (McGarvey et al. 2003). It was apparent from several sets
of data that the abundances of this species across the South Australian fishery had decreased
considerably through the period of 1999 to 2002. This concerning status prompted a review of
the management of the fishery through 2004 that culminated in significant changes that came into
force on the 1st October 2004. The subsequent two stock assessments that have been done after
this implementation were completed in August 2005 (McGarvey et al. 2005) and August 2008
(Fowler et al. 2008). Both reports provided opportunities to assess whether the downward trends
in biological performance indicators that were evident through the period of 1999 to 2002 had
continued or not. The first report suggested that there had been a turn-around in the downward
trend of the fishery. The second report indicated through commercial fishery statistics, output
parameters from WhitEst and the assessment of fishery performance indicators that the status of
the fishery had improved considerably and that, at that time in 2008, there was no immediate
concern about the status of South Australia’s King George Whiting fishery.
The current stock assessment report provides opportunity to assess the status of the King George
Whiting fishery from data collected up to the end of 2010, i.e. approximately six years after the
new management changes were implemented. There were several sets of data considered that
relate the status of the fishery. Firstly, the commercial catch, effort and CPUE data were
considered at both the State-wide and regional scales. Secondly, the size and age structures of
populations at various places across the fishery were considered. Finally, these two independent
datasets were then integrated in the WhitEst fishery assessment model, to generate a number of
output parameters as indicators of fishery status. The various fishery performance indicators were
assessed against prescribed limit reference points.
8.2 Determination of stock status
Commercial fishery statistics
The most complete and informative data on the status of the King George Whiting stocks are the
estimates of catch, effort and CPUE from the commercial fishing sector. Given that large areas of
81
the State are now closed to net fishing, and that net fishing effort in the remaining areas continues
to decline, it is considered that the statistics for hauling nets and gillnets may no longer be strongly
indicative of fishable biomass. As such, strong emphasis has been placed in this report on the
statistics from the commercial handline sector. We presented the handline data for the calendar
years of 1984 to 2010, thus providing an additional three years of data subsequent to those
reported by Fowler et al. (2008). The dominant long-term trend in these 27-year datasets has been
a steady decline in commercial fishing effort, particularly between 1992 and 2005. Subsequent to
2005, the rate of decline has slowed and the State-wide estimates of handline catch and effort have
been relatively stable. The decline up to 2005 was driven by an on-going reduction in the number
of Marine Scalefish commercial fishers, particularly as a consequence of the Licence
Amalgamation Scheme. This rate of decline has fallen, which has lead to more stable fishing
effort in recent years. The decline in licence holders up to 2005 has resulted in less fishing days,
culminating in a general reduction in commercial catch. Prior to 1999, these reductions in
commercial catch and effort were generally associated with estimates of rising CPUE. However,
between 1999 and 2002 there were declines in the regional estimates of CPUE that were the
primary cause for concern with respect to stock status throughout that period. In each region,
handline CPUE increased after 2002 at least for several years. For each of the FWC, MWC and
KI the recovery in handline CPUE continued until 2010, when there were notable declines. For
each of CB, SSG, NSG and GSV, CPUE recovered until 2007 after which there was some decline.
Overall, these data are indicative of higher levels of fishable biomass subsequent to 2002, and then
a levelling off of these increases between 2007 and 2010.
In this report, general fishery performance indicators determined from the commercial fishery
statistics were considered at two spatial scales, i.e. at the State-wide scale for each year from 2008
to 2010 and then also regionally for the fishery statistics from 2010. At the State-wide scale, there
were a few breaches of limit reference points: two related to the low catches of King George
Whiting in the last three years; with the last related to the record high catch rate that was recorded
in 2009. There were also several breaches of limit reference points for the handline fishery
statistics from 2010 for particular regions, which generally related to low catch levels or high catch
rates. The triggered limit reference points that related to low catches were recorded across the
spatial range of the fishery for each of the FWC, NSG, GSV and KI. Alternatively the breached
limit reference points relating to high catch rates were limited to the neighbouring regions of
MWC and CB. None of these breaches are of particular concern with respect to the level of
fishable biomass available to fishers. There was one triggered limit reference point that related to
a dramatic drop in handline CPUE that was recorded for KI between 2009 and 2010. Although
this is not of immediate concern because it represents a decline in only a single year, nevertheless it
should be monitored in the future.
82
Population structure
The second set of data considered as indicators of stock status were population size and age
structures. Through broad-scale population sampling during the 1990s it became evident that
King George Whiting in South Australia are not distributed evenly with respect to size and age
(Fowler and McGarvey 2000, Fowler et al. 2000). Whilst some populations consist of relatively
small, young fish, others support broader age and size ranges of individuals. The latter form the
spawning aggregations during the reproductive season (Fowler et al. 1999), which are
supplemented by movement of small, young adults from the inshore areas (Fowler et al. 2002).
The different size and age distributions of fish in different regions are the culmination of a
complicated sequence of life history and demographic processes. As such, we consider that the
regional estimates of population structure provide significant indicators of stock status. In this
study, market sampling for King George Whiting was undertaken across the geographic range of
the fishery during each financial year of 2006/07, 2008/09 and 2009/10 and the size and age
distributions were considered against historical data. These comparisons did not provide any
evidence of significant change in population structure across the range of the species in South
Australia that could be attributable to the fishery. As such, the limit reference points for this
indicator were not activated for any of the three primary fishery regions.
Computer fishery assessment model
The computer fishery assessment model ‘WhitEst’ integrates the fishery and biological data to
provide annual estimates of recruitment, fishable biomass and annual exploitation rate. As
reported by McGarvey et al. (2003), up to 2002 there were some concerning trends in these
estimated output parameters. In contrast, up to the end of 2010, the trends in output parameters
displayed much more positive trends. For the West Coast, the estimates of recruitment increased
between 2002 and 2010 with a notable peak in 2009. Consequently, the trend in fishable biomass
increased appreciably between 2004 and 2010. Furthermore, the exploitation rate in this region
fell between 2003 and 2008 and remained at low levels in 2009 and 2010. None of the limit
reference points were activated for these biological performance indicators, suggesting no cause
for concern about the King George Whiting fishery on the West Coast.
The trends in output parameters from WhitEst for Spencer Gulf were similar to those for the
West Coast. Fishable biomass increased from 2004 onwards, before declining marginally in 2010.
Recruitment was relatively consistent through this period whilst estimated exploitation rate in this
region declined annually from 1997 to the lowest recorded level in 2010. There was one limit
reference point activated for this region, i.e. the most recent estimate of recruitment was 18%
83
below the average of the previous 5 years. This was driven largely by a high recruitment rate in
2005, which dragged the previous 5 year average upwards considerably. Consequently, overall the
output parameters from WhitEst are not cause for concern about the current status of the fishery
in Spencer Gulf.
The estimates of output parameters for GSV are marginally more concerning than for the other
two regions. Firstly, the fishable biomass has always been much lower, reflecting the lower level
of recruitment experienced in this region. The fishable biomass has only increased at a very low
rate from a low base over time. Furthermore, the WhitEst model has estimated a marginally
increasing exploitation rate in this region since 2001. This is on the basis of the estimated increase
in recreational fishing effort in this region throughout the 2000s. Overall, despite the marginally
increasing exploitation rate, the King George Whiting fishery in GSV has been relatively stable
and so is not cause for immediate concern.
8.3 Uncertainty in the fishery
The primary uncertainty about the assessment of stock status for the regional fisheries for King
George Whiting presented here, relates to our lack of a comprehensive understanding of the
temporal trends in catch and effort by the recreational sector in the different fishery regions.
Since the completion of the last stock assessment in 2008 (Fowler et al. 2008), the results from the
2007/08 South Australian Recreational Fishing Survey have been released (Jones 2009,
summarised in Chapter 4). The results from that survey reinforced that the recreational sector
does account for a significant proportion of the total catch across South Australia, i.e.
approximately 50% of the total. The results also indicated that there had been considerable
changes in the levels of catch and effort since 2000/01, but these were consistent across the spatial
range of the fishery. Whilst overall participation in recreational fishing in SA had declined from
2000/01 (Jones 2009), which led to lower effort in such regions as the WC and NSG, effort and
catch increased in GSV and KI. Given the complicated nature of these results, further data are
required to confirm the temporal trends. This is further complicated by the fact that inter-state
fishers were excluded from the survey in 2007/08. Nevertheless, despite the uncertainty about the
results, they still had to be used in the WhitEst model to calculate trends in output parameters
because the recreational effort is so high. Since annual data are not available for the recreational
sector for incorporation into WhitEst, annual estimates were calculated based on the results from
the two State-wide telephone/ diary surveys. For example, the recreational catch and effort data
for the years prior to 2000/01 were estimated to vary from the 2000/01 figures, proportionally
with the size of the human population. In reality it is unlikely that such estimates provide a
satisfactory time series of recreational catch and effort as they do not accommodate a changing
84
participation rate in recreational fishing or changes to effective effort through increasing
technology available to this sector. Nevertheless, until the results from further recreational fishing
surveys are available in the future, the stock assessment process will have to rely on the use of
such estimated values with their inherent levels of uncertainty.
8.4 Management implications
The new management regulations that were implemented in October 2004 raised the minimum
legal size, reduced recreational bag and boat limits and sought to accelerate the rate of commercial
licence amalgamation. It is now more than six years since those management changes were
implemented. The various fishery performance indicators considered in this study are all relatively
consistent in suggesting that in general the fishery is stable at present and that there are no
downward trends of sufficient duration or magnitude that would raise alarm about the status of
the stocks. As such, there appears to be no immediate requirement to reconsider the current
management regulations for South Australia’s King George Whiting fishery.
8.5 Future work
The various monitoring programs for the King George Whiting fishery that were described in this
report will continue into the future. These include the monitoring of the commercial catch and
effort data and that from the Charter Boat sector by SARDI’s Information Systems and Database
Support Program. Market sampling for King George Whiting has been done in 2004/05,
2006/07, 2008/09 and 2009/10 to describe the spatial variation in population size and age
structures. This market sampling will continue in the future and is currently planned for the
period of October 2011 to September 2013. These data will be used to inform the WhitEst
fishery assessment model for future stock assessments, and to monitor for contractions in size and
age structures. It is likely that catch and effort data will need to be collected for the recreational
sector every five years or so to describe the temporal trends and to ensure that the various fishery
sectors continue to conform to their allocated share over time. The next stock assessment is
planned for the financial year of 2013-2014 to be delivered in July 2014.
85
9. REFERENCE LIST
Australian Bureau of Agricultural and Resource Economics (ABARE) (2007). Australian Fisheries Statistics, 2006. Canberra.
Berkeley SA, Hixon MA, Larson RJ, Love MS (2004) Fisheries sustainability via protection of age structure
and spatial distribution of fish populations. Fisheries 29: 23-32. Bruce BD (1989) Studying larval fish ecology: benefits to King George Whiting research. SAFISH 13: 4-9. Coleman FC, Figueira WF, Ueland JS and Crowder LB (2004) The impact of United States recreational
fisheries on marine fish populations. Science 305: 1958-1960. Fowler AJ (1998) King George Whiting (Sillaginodes punctata). South Australian Fisheries Assessment Series
98/6. 58 pp. Fowler AJ, March WA (2000) Characteristics of movement of King George Whiting (Percoidei:
Sillaginidae) in South Australian waters. Fish Movement and Migration. Australian Society of Fish Biology Workshop, Bendigo 28-29th Sept. 1999. pp. 136-143.
Fowler AJ, McGarvey R (1997) King George Whiting (Sillaginodes punctata). South Australian Fisheries
Assessment Series 97/6. 93 pp. Fowler AJ, McGarvey R (1999) King George Whiting (Sillaginodes punctata). South Australian Fisheries
Assessment Series 99/03. 41 pp. Fowler AJ, McGarvey R (2000) Development of an integrated fisheries management model for King
George Whiting (Sillaginodes punctata) in South Australia. Final report to FRDC for project 95/008. 232 pp.
Fowler AJ, Short DA (1996) Temporal variation in the early life-history characteristics of the King George
Whiting (Sillaginodes punctata) from analysis of otolith microstructure. Marine and Freshwater Research 47: 809-818.
Fowler AJ, Short DA (1998) Validation of age determination from otoliths of the King George Whiting
Sillaginodes punctata (Perciformes). Marine Biology 130: 577-587. Fowler AJ, Jones GK, and McGarvey R (2002). Characteristics and consequences of movement patterns of
King George Whiting (Perciformes: Sillaginodes punctata) in South Australia. Marine and Freshwater Research 53: 1055-1069.
Fowler AJ, McLeay L, Short DA (1999) Reproductive mode and spawning information based on gonad
analysis for the King George Whiting (Percoidei: Sillaginidae) from South Australia. Marine Freshwater Research 50: 1-14.
Fowler AJ, McLeay L, Short DA (2000a) Spatial variation in size and age structures and reproductive
characteristics of the King George Whiting (Percoidei: Sillaginidae) in South Australian waters. Marine and Freshwater Research 51: 11-22.
Fowler AJ, Black KP, Jenkins GP (2000b) Determination of spawning areas and larval advection pathways
for King George Whiting in south-eastern Australia using otolith microstructure and hydrodynamic modelling. II. South Australia. Marine Ecology Progress Series 199: 243-254.
Fowler AJ, McGarvey R, Feenstra JE (2008) King George Whiting (Sillaginodes punctata) Fishery. Fishery
Assessment Report to PIRSA Fisheries. South Australian Research and Development Institute (Aquatic Sciences), Adelaide, 77 pp. SARDI Publication Number F2007/000843-2. SARDI Research Report Series No. 296.
Francis RC (2003) A web of small tensions. Fisheries 28: 20-23.
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Haigh LJ, Donnellan S (2000) Stock structure based on analysis of mitochondrial DNA and microsatellites.
In: (Fowler AJ, McGarvey R, eds) Development of an integrated fisheries management model for King George Whiting (Sillaginodes punctata) in South Australia. Final Report to FRDC for project 95/008. pp 105-124.
Henry GW, Lyle JM (2003) The National Recreational and Indigenous Fishing Survey. Final Report to
FRDC for project 99/158. 200 pp. Jenkins GP (2005) Influence of climate on the fishery recruitment of a temperate, seagrass-associated fish,
the King George Whiting Sillaginodes punctata. Marine Ecology Progress Series 288: 263-271. Jenkins GP, Black KP, Hamer PA (2000) Determination of spawning areas and larval advection pathways
for King George Whiting in southeastern Australia using otolith microstructure and hydrodynamic modelling. I. Victoria. Marine Ecology Progress Series Vol 199: 231-242.
Jones GK (2009) South Australian Recreational Fishing Survey. PIRSA Fisheries, Adelaide, 84 pp. South
Australian Fisheries Management Series Paper No. 54. Jones GK, Hall DA, Hill KM, Staniford A (1990) The South Australian marine scalefish fishery: stock
assessment, economics, management. South Australian Department of Fisheries green Paper. 186 pp.
Jones GK, Doonan A (2005) 2000-01 National Recreational and Indigenous Fishing Survey. South
Australian Regional Information. South Australian Fisheries Management Series. Paper No. 46. Knight M (2009). The South Australian Recreational Charter Boat Fishery Report 2009. South Australian
Research and Development Institute (Aquatic Sciences), Adelaide, 46 p. SARDI Publication No. F2007/000847-2.
Knight MA, Doonan AM, Tsolos A (2007) South Australian wild fisheries information and statistics report.
South Australian Research and Development Institute (Aquatic Sciences), Adelaide, F2007/000571-1. SARDI Research Report Series No. 200.
Longhurst A (1998) Cod: perhaps if we stood back a bit? Fisheries Research 38: 101-108. McGarvey R, Feenstra JE (2002) Estimating rates of fish movement from tag-recoveries: conditioning by
recapture. Canadian Journal of Fisheries and Aquatic Sciences 59: 1054-1064. McGarvey R, Fowler AJ (2002) Seasonal growth of King George Whiting (Sillaginodes punctata) from length-
at-age samples truncated by legal minimum size. Fishery Bulletin 100: 545-558. McGarvey R, Feenstra JE, Fowler AJ (2000) King George Whiting (Sillaginodes punctata). South Australian
Fisheries Assessment Series 00/03. 47 pp. McGarvey R, Fowler AJ, Feenstra JE, Fleer DA, Jones GK (2003) King George Whiting (Sillaginodes
punctata). SARDI Aquatic Sciences Publication No. RD03/0152. 76 pp. McGarvey R, Fowler AJ, Feenstra JE, Jackson WB and Jennings PR (2005). King George Whiting
(Sillaginodes punctata) fishery. Fishery Assessment Report to PIRSA for the Marine Scalefish Fishery Management Committee. South Australian Research and Development Institute (Aquatic Sciences), Adelaide RD03/0152-2.
McGarvey R, Feenstra JE, Ye Q (2007) Modeling fish numbers dynamically by age and length: partitioning
cohorts into ‘slices’. Canadian Journal of Fisheries and Aquatic Sciences 64: 1157-1173. McGlennon D, Kinloch MA (1997) Resource allocation in the South Australian marine scalefish fishery.
FRDC project 93/249, Final Report. 105 pp. Moran SM, Jenkins GP, Keough MJ, Hindell JS (2004) Evidence for secondary planktonic transport of
post-larvae of seagrass-associated King George Whiting. Journal of Fish Biology 64: 1226-1241.
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Noell C, Presser J, Jones K (2006) Management Plan for the South Australian Marine Scalefish fishery. The South Australian Fisheries Management Series Paper No. 45. 68 pp.
Platell ME, Orr PA, Potter IC (2006) Inter- and intraspecific partitioning of food resources by six large and
abundant fish species in a seasonally open estuary. Journal of Fish Biology 69: 243-262. Robertson, AI (1977) Ecology of juvenile King George Whiting Sillaginodes punctata (Cuvier +
Valenciennes) (Pisces: Perciformes) in Western Port, Victoria. Australian Journal of Marine and Freshwater Research 28: 35-43.
Taylor BL, Dizon AE (1996) The need to estimate power to link genetics and demography for
conservation. Conservation Biology 10: 661-664.
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10. APPENDIX: MODEL FITS TO DATA
Parameters and thus stock indicators in the WhitEst model are estimated by fitting to data for
commercial catch totals by weight, recreational catch total numbers, and to commercial catch
proportions by age and sex, in each month when sampling occurs. Due to space limitations, only
model fits to the reported monthly King George Whiting catch totals are shown in this report
Appendix, for the 5 principal subregions, in Fig 11.1 below. Plots of fit to the extensive age
samples are available upon request for the five subregions and both sexes, and for each month of
the two age and length sampling programs which ran from September 1994 to June 1997, from
July 2004 to June 2007, and July 2008 to December 2010.
89
0
20
40
DataModel
West Coast
Com
mer
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cat
ch (t
onne
s)
Model time-step
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Northern Spencer Gulf
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Southern Spencer Gulf
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Northern Gulf St. Vincent
0
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10DataModel
Southern Gulf St. Vincent
Jan
84 -
Jan
85 -
Jan
86 -
Jan
87 -
Jan
88 -
Jan
89 -
Jan
90 -
Jan
91 -
Jan
92 -
Jan
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Jan
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Jan
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Jan
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Fig. 11.1. Fits of model to data monthly commercial catch totals (all gears and target types), for the 5 principal King George Whiting regions.
