W. Koster and T.A. Raadik - West Gippsland...Migratory freshwater fish comprise about 70% of the native freshwater fish fauna of the coastal-draining Thomson River system in West Gippsland

7

Review of diadromous fish distribution in the upper Thomson River system

W. Koster and T.A. Raadik

2010

Arthur Rylah Institute for Environmental Research

Client Report

Arthur Rylah Institute for Environmental Research Client Report


W. Koster and T.A. Raadik

Arthur Rylah Institute for Environmental Research 123 Brown Street, Heidelberg, Victoria 3084

2010

Arthur Rylah Institute for Environmental Research Department of Sustainability and Environment

Heidelberg, Victoria

Report produced by: Arthur Rylah Institute for Environmental Research

Department of Sustainability and Environment

PO Box 137

Heidelberg, Victoria 3084

Phone (03) 9450 8600

Website: www.dse.vic.gov.au/ari

© State of Victoria, Department of Sustainability and Environment 2010

This publication is copyright. Apart from fair dealing for the purposes of private study, research, criticism or review as

permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any means

(electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department of

Sustainability and Environment. All requests and enquiries should be directed to the Customer Service Centre, 136 186

or email [email protected]

Citation: Koster, W. and Raadik, T.A. 2010. Review of diadromous fish distribution in the upper Thomson River

system. Report to West Gippsland Catchment Management Authority. Department of Sustainability and Environment,

Heidelberg, Victoria (unpublished).

Disclaimer: This publication may be of assistance to you but the State of Victoria and its employees do not guarantee

that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore

disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in

this publication.

Front cover photo: Australian Grayling (Tarmo A. Raadik) and upper Thomson River (Wayne Koster).

Authorised by: Victorian Government, Melbourne

Printed by: Snap Printing, Heidelberg

iii

Contents

Acknowledgements............................................................................................................................v

Summary............................................................................................................................................1

1 Background .............................................................................................................................3

2 Distribution of Australian Grayling and other diadromous fish in the upper Thomson

River system.......................................................................................................................................4

Australian Grayling (Prototroctes maraena) ......................................................................................5

Lampreys (Mordacia mordax and Geotria australis ) ........................................................................5

Eels (Anguilla australis and A. reinhardtii) ........................................................................................6

Broad-finned Galaxias (Galaxias brevipinnis)....................................................................................6

Common Galaxias (Galaxias maculatus) ...........................................................................................7

Australian Bass (Macquaria novemaculeata) .....................................................................................7

Tupong (Pseudaphritis urvillii)...........................................................................................................8

3 Factors impeding the distribution of Australian Grayling and other diadromous fish in

the upper Thomson River system ....................................................................................................9

4 Restoring connectivity of fish passage for Australian Grayling and other diadromous

fish in the upper Thomson River system.......................................................................................12

5 Conclusions and recommendations .....................................................................................15

iv

v

Acknowledgements

The West Gippsland Catchment Management Authority (WGCMA) funded this project. Thanks to

David Stork from WGCMA for his role in the coordination of the project. David Crook, Jason

Lieschke, Jeremy Hindell and Matthew Jones from the Arthur Rylah Institute for Environmental

Research (ARI) provided valuable comments on an earlier version of this document. Thanks to

David Dawson from ARI for his assistance in collating fish distribution data.

vi


Arthur Rylah Institute for Environmental Research Client Report 1

Summary

This report documents the findings of a review of the distributions of diadromous fish in the upper

Thomson River system in West Gippsland. Diadromous fish undertake migrations between

freshwater and marine environments and comprise about 70% of the native freshwater fish species

in the Thomson River system. They are currently considered to be confined largely to the lower

and mid reaches (Hall 1989, Raadik 1996, Koster and Crowther 2003).

Specifically, the aim of this project was to determine the distributions of the nationally threatened

Australian Grayling (Prototroctes maraena) and other diadromous fish species in the upper

Thomson and Aberfeldy rivers, and identify, where possible, any factors potentially impeding

diadromous fish distribution, based on a review of fish survey data and published and grey

literature (including technical reports).

The results of this review indicate that Australian Grayling and most other diadromous fish species

in the Thomson River system are confined to the lower and mid reaches. Exceptions include eels

and lampreys, which are capable of climbing over barriers. Based on historic, current and potential

distributions of diadromous fish species, including comparisons with the fish communities present

in nearby catchments (e.g. Mitchell, Tambo, Snowy), Australian Grayling and several other

diadromous fish species should be found in the upper reaches of the system.

A range of factors are potentially impacting diadromous fish distribution in the mid to upper

Thomson River. The Thomson Dam has modified the hydrology and water temperature of the

river, which could result in the loss or disruption of important biological cues (e.g. high flows) for

fish migrating into the system or throughout the river (TMEFT 2004). Issues with coldwater

releases have been alleviated to some degree by the use of a multi-level offtake to maintain release

water temperatures within target levels. The presence in the upper Thomson River of the

diadromous Short-finned Eel (Anguilla australis), Long-finned Eel (Anguilla reinhardtii) and

lampreys (Mordacia mordax, Geotria australis) suggests that suitable migration/attraction cues

(i.e. flows) exist in the upper reaches. The presence of self-sustaining populations of non-

migratory native fish species (e.g. Southern Pygmy Perch Nannoperca australis, River Blackfish

Gadopsis marmoratus, Australian smelt Retropinna semoni) in the Thomson River below the dam

also indicates that water temperature and flow are not preventing the establishment of fish

populations in the upper Thomson River and that native fish are able to survive in this reach.

The degree of impact of recent fires on fish habitat in the upper Thomson River catchment is

unknown, but is not likely to be a major cause of the lack of diadromous fish species in that part of

the system. Given that diadromous fishes in south-eastern Australia typically undertake annual

upstream migrations from marine environments into rivers, and different species migrate at

different times, at least some diadromous fish species should be present at any given time. Even if

habitat was extremely unsuitable, small numbers of fish would be present, replaced by new

recruits (Lyon and O’Connor 2008). Surveys conducted in the Thomson River since the fires have

collected the diadromous species Australian Grayling, Tupong (Pseudaphritis urvillii) and

Common Galaxias (Galaxias maculatus) at various sites in areas that were burnt (e.g. Coopers

Creek, C5 Track, Bruntons Bridge), but not from sites upstream of the Horseshoe Bend Tunnel.

The Horseshoe Bend Tunnel on the upper Thomson River has been identified in the Victorian

State Fishway Program as a barrier to fish movement (McGuckin and Bennett 1999). The tunnel

was constructed in 1911–12 with most of the river flow diverted through the tunnel and bypassing

the one kilometre reach of the Thomson River known as Horseshoe Bend (LCC 1991).

Opportunities for fish to migrate through the old river channel are limited, as the flow in the

channel is estimated to occur about 3% of the time (Koster and Crowther 2003). In contrast,

diadromous fishes in south-eastern Australia migrate over an extensive time frame encompassing


2 Arthur Rylah Institute for Environmental Research Client Report

much of the year (Koehn and O’Connor 1990). Migration of fish through the tunnel would also be

impeded, particularly by steep gradients and sudden drops in height. Water velocities within the

tunnel (1.2–6.2 m/sec) are also known to far exceed the swimming capabilities of small

diadromous fishes (Saddlier and O’Connor 1997, Boubee et al. 1999). Natural light within the

tunnel is also severely reduced, which can be a behavioural impediment to fish movement

(O’Brien 1999, Thorncraft and Harris 2000, Fairfull and Witheridge 2003).

Restoring fish passage connectivity around the Horseshoe Bend Tunnel along the old course of the

Thomson River would increase the opportunities for the Australian Grayling and other diadromous

fish species to access the upper reaches of the system. Restoring fish passage past the tunnel

supports the need to restore access to rivers for Australian Grayling in accordance with the

National Recovery Plan for Australian Grayling (Backhouse et al. 2008) and represents an

important step toward restoring connectivity and biodiversity of native fish communities in the

Thomson River system. Restoring fish passage past Horseshoe Bend Tunnel would facilitate

access to a further 22 km of the Thomson River upstream to the Thomson Dam, 63 km of the

Aberfeldy River, and numerous tributary streams, including streams in the Baw Baw National

Park. Recommendations on the timing and magnitude of flows to facilitate fish passage along the

old course of the Thomson River around Horseshoe Bend Tunnel are also provided.



1 Background

Approximately 70% of native freshwater fish species in coastal catchments in Victoria exhibit

diadromy (Harris 1984, Koehn and O’Connor 1990, Raadik 1995, Drew 2008) - they undertake

migrations between freshwater and marine environments (McDowall 1988). Several different

kinds of diadromy exist, including anadromy, catadromy and amphidromy (Myers 1949,

McDowall 1988). Anadromous fish enter rivers as mature adults and migrate to upstream

spawning grounds, with juveniles later migrating downstream to the sea (e.g. Short-headed

Lamprey Mordacia mordax, Pouched Lamprey Geotria australis, Australian Whitebait Lovettia

sealii) (McDowall 1999). Catadromous fish enter rivers as juveniles, and adults return to the sea to

spawn (e.g. Tupong Pseudaphritis urvillii, Short-finned Eel Anguilla australis, Long-finned Eel

Anguilla reinhardtii). Adult amphidromous fish live and spawn in fresh water, and the larvae drift

downstream to the sea and later migrate back into fresh water (e.g. Australian Grayling

Prototroctes maraena, Broad-finned Galaxias Galaxias brevipinnis) (McDowall 1999).

In all categories of diadromy, migrations are undertaken by different life-history stages, and

consequently by different sizes of fish (e.g. adults, juveniles and larvae). Swimming ability varies

with each life history stage and between species and consequently the speed of movement and the

degree of penetration (or distance inland) upstream into freshwater environments varies.

Migratory freshwater fish comprise about 70% of the native freshwater fish fauna of the coastal-

draining Thomson River system in West Gippsland. The current distribution of Australian

Grayling and most of the other migratory fish species is considered to be confined to the lower and

mid reaches (Hall 1989, Raadik 1996, Koster and Crowther 2003). Australian Grayling is a

nationally threatened species, and is listed as vulnerable under the Commonwealth Environment

Protection and Biodiversity Conservation Act 1999 and threatened under the Victorian Flora and

Fauna Guarantee Act 1988. Key threats to Australian Grayling include barriers to migration,

altered flow regimes and habitat loss and degradation (Backhouse et al. 2008, DEWHAC 2010). In

the national recovery plan for the Australian Grayling, preservation of the Thomson River

population is identified as necessary for the long-term survival and recovery of the species

(Backhouse et al. 2008).

The aim of this project was to determine the distributions of Australian Grayling and other

diadromous fish in the upper Thomson and Aberfeldy rivers, and identify, where possible, any

factors potentially impeding diadromous fish distribution, based on a review of published and grey

literature (including technical reports) and fish survey data (Victorian Aquatic Fauna Database

managed by the Arthur Rylah Institute for Environmental Research - ARI). The report also

addresses a number of particular concerns (e.g. alien fish species, fish stocking) regarding

reinstating or improving diadromous fish passage in the system.



2 Distribution of Australian Grayling and other diadromous fish in the upper Thomson River system

Data on fish distributions in the Thomson River basin, and from more widely in coastal Victoria,

where applicable, has been sourced from the Victorian Aquatic Fauna Database and published and

grey literature (including technical reports). Survey data extends back to the mid 1960s. Earlier

surveys (i.e. pre mid 1980s) were typically focused on recreational angling species (native and

exotic), and may not have targeted or recorded all native non-angling species. The actual

distributions of native non-angling species in the Thomson River system in this earlier period may

therefore be under-represented. Data on the occurrence of native migratory species in adjacent or

nearby similar coastal catchments were included to provide support for possible historic ranges

within the Thomson River system. More recent surveys conducted in the Thomson River system

have been designed to provide representative information on species distributions or biodiversity

(e.g. Saddlier and Doeg 1998, 2002, Koster and Crook 2006, Koster and Dawson 2008, Koster et

al. 2009, Lieschke unpublished [Sustainable Rivers Audit - SRA] data). No fish survey data was

available for the upper Thomson River system prior to construction of the Horseshoe Bend Tunnel

(1911–12), located on the upper Thomson River upstream of Coopers Creek.

Ten native freshwater migratory fish species have been recorded from the Thomson River basin to

date (Table 1), including the Australian Smelt (Retropinna semoni), which was recently found to

be partly diadromous (Crook et al. 2008a). As diadromy appears to be facultative (not obligatory)

in Australian Smelt because only some individuals or populations undertake migrations, this

species was not considered further in the review.

Table 1. Common and scientific names of migratory freshwater native fish recorded from the

Thomson River basin, including migratory phases.

Migration direction and life stage

Common Name Scientific Name Downstream Upstream

Short-headed Lamprey Mordacia mordax Juvenile Adult

Pouched Lamprey Geotria australis Juvenile Adult

Short-finned Eel Anguilla australis Adult Juvenile

Long-finned Eel Anguilla reinhardtii Adult Juvenile

Broad-finned Galaxias Galaxias brevipinnis Larvae Juvenile

Common Galaxias Galaxias maculatus Adult + larvae Juvenile

Australian Grayling Prototroctes maraena Adult + larvae Juvenile

Australian Smelt Retropinna semoni Larvae Juvenile

Australian Bass Macquaria novemaculeata Adult + larvae Juvenile

Tupong Pseudaphritis urvillii Adult Juvenile



Australian Grayling (Prototroctes maraena)

Australian Grayling adults undertake downstream migrations to the lower reaches of rivers during

autumn to spawn, usually coinciding with rises in flow, then migrate back upstream (Koster and

Dawson 2010a,b). The larvae are washed downstream to the sea, where they remain for about five

months before returning back upstream as juveniles into the freshwater reaches of rivers in spring–

summer (Berra 1982, 1987; Crook et al. 2006).

Australian Grayling have been recorded in the Thomson River as far upstream as Walhalla, where

a single individual was collected near the bridge on the Walhalla Road in 1985 at 220 metres

above sea level (masl) (approx. river distance inland 160 km). This is the only known record of the

species in the system upstream of the Horseshoe Bend Tunnel, despite numerous recent surveys

(i.e. late 1990s onwards) in the upper Thomson River designed to provide representative

information on species distributions or biodiversity (e.g. Saddlier and Doeg 1998, 2002, Koster

and Crook 2006, Koster and Dawson 2008, Koster et al. 2009, Lieschke unpublished SRA data).

Australian Grayling have been recorded, however, at several nearby sites (e.g. Coopers Creek –

200 masl, C5 Track – 190 masl, Bruntons Bridge – 190 masl), but these are all downstream of the

tunnel in surveys since the mid 1980s. The sites at Coopers Creek, C5 Track and Bruntons Bridge

are located approximately one, three and nine kilometres downstream of the tunnel, respectively.

Throughout its range, the Australian Grayling is known to occur at high altitudes and is able to

move large distances inland. For example, Australian Grayling have been recorded in the

Wonnangatta River to 400 masl (approx. river distance inland 230 km), the Tambo River near

Bindi Station at 440 masl (approx. river distance inland 160 km) and in Craigie Bog Creek (Snowy

River system) to 760 masl (approx. river distance inland 340 km). Australian Grayling could be

expected to occur in the upper reaches of the Thomson River system to about 400–450 masl,

including the lower reaches of the Aberfeldy River. This is much higher than the current range of

190–220 masl. It should also be noted that this range is based on records following construction of

the Horseshoe Bend Tunnel (1911–12).

Lampreys (Mordacia mordax and Geotria australis )

Two species of lamprey have been recorded from the Thomson River system — the Short-headed

Lamprey and Pouched Lamprey. Adult lampreys migrate upstream in winter–spring and spawn in

the upper reaches of rivers (Koehn and O’Connor 1990, McDowall 2000). Juveniles gradually

migrate downstream and go to sea the following winter, remaining there for 3–4 years before

returning to fresh water as adults (McDowall 2000).

Short-headed Lamprey have been recorded at several sites upstream (e.g. The Narrows, Walhalla

Road Bridge) and downstream (e.g. Coopers Creek, C5 Track, Bruntons Bridge) of Horseshoe

Bend Tunnel in various surveys from the mid 1980s to the present. Pouched Lamprey have been

recorded in the Thomson River upstream to The Narrows in the mid to late 1980s, and

occasionally farther downstream in the system (e.g. Bruntons Bridge, Cowwarr, Rainbow Creek).

Throughout their range, both species of lamprey are known to penetrate large distances inland and

upstream to high altitudes. For example, Short-headed Lamprey have been recorded in the Tambo

River near Bindi Station to 440 masl (approx. river distance inland 160 km) and Menaak Creek to

350 masl (approx. river distance inland 155 km). Pouched Lamprey have been recorded in the

Brodribb River to 240 masl (approx. river distance inland 85 km) and up to 300 masl in the Yarra

River system (approx. river distance inland 130 km).



Both species of lamprey should occupy the lower to mid reaches of the Thomson River system,

with Pouched Lamprey upstream to about 300 masl and Short-headed Lamprey penetrating farther

upstream to over 400 masl, including the lower reaches of the Aberfeldy River. Lampreys are

known to climb wet rocks and vertical surfaces (Harris 1984, Sloane 1984), so they can be found

upstream of instream obstacles.

Eels (Anguilla australis and A. reinhardtii)

Two species of eels — the Short-finned Eel and Long-finned Eel — are found in the Thomson

River system. Adults migrate downstream to the sea to spawn during summer–autumn with

migration documented as being associated with high flow events (Koehn and O’Connor 1990,

Crook et al. 2008b). Juveniles enter fresh water during spring and summer (Koehn and O’Connor

1990). Short-finned Eels can withstand periods out of water and can climb over substantial

barriers, although this behaviour is most common in the juvenile phase (<120 mm) (McDowall

2000).

Short-finned Eel have been recorded in the Thomson River as far upstream as the Thomson–

Jordan Divide Road, upstream of Thomson Dam in 1988 (500 masl, approx. river distance inland

200 km) and have been recorded at several sites (e.g. Beardmores Track, The Narrows, Walhalla

Road Bridge) upstream of Horseshoe Bend Tunnel, as well as in the Aberfeldy River, in various

surveys since the late 1970s. Short-finned Eel have also been recorded downstream of Horseshoe

Bend Tunnel at several nearby sites (e.g. Coopers Creek, C5 Track, Bruntons Bridge) in various

surveys since the late 1970s. Long-finned Eel have been recorded at several sites upstream (e.g.

The Narrows, Walhalla Road Bridge) and downstream (e.g. Coopers Creek, C5 Track, Bruntons

Bridge) of Horseshoe Bend Tunnel in various surveys between the 1980s and the present.

Throughout their range, Short-finned and Long-finned Eels are known to penetrate to high

altitudes and large distances inland, and Short-finned Eel may penetrate as far as headwater

reaches. For example, Short-finned Eel have been recorded in the Wonnangatta River to 400 masl

(approx. river distance inland 230 km), the Tambo River north branch and Bendoc River to

960 masl (approx. river distance inland 185 km and 355 km respectively), with individuals found

as high as 1340 masl in the upper Snowy River system (approx. river distance inland 350 km).

Long-finned Eel have been recorded in the Crooked River to 370 masl (approx. river distance

inland 200 km), the Tambo River south branch to 560 masl (approx. river distance inland 170 km)

and Butchers Creek (620 masl, approx. river distance inland 110 km), with the highest recorded

elevation in the Snowy River catchment at 755 masl (approx. river distance inland 360 km).

Consequently, Short-finned Eel are expected to be found throughout the Thomson River

catchment, including the upper reaches, with Long-finned Eel penetrating upstream to

approximately 450–500 masl including the lower and mid reaches of the Aberfeldy River.

Broad-finned Galaxias (Galaxias brevipinnis)

Broad-finned Galaxias adults spawn in the upper reaches of streams during autumn on high flows

(O’Connor and Koehn 1998). Larvae are then washed downstream to the sea and move into rivers

and migrate upstream as juveniles about six months later, during spring (Koehn and O’Connor

1990, McDowall 2000). Broad-finned Galaxias are also known to form landlocked populations in

many lakes (McDowall 2000).

Only a single individual Broad-finned Galaxias has been recorded in the Thomson River, from the

mid reaches near Cowwarr in 2002. The species is relatively uncommon in the entire Gippsland



Lakes catchments (Tambo, Mitchell, LaTrobe and Thomson River basins) with only a few

populations known from the lower Mitchell and Avon River systems, though a landlocked

population exists in Lake Tarli Karng in the Macalister River system (Thomson River basin).

Given the difficulty in identification of Broad-finned Galaxias in the juvenile stage

(morphologically similar to other Galaxias spp.), the available dataset for this species in the

Thomson River system is considered to be poor.

Throughout its range in Victoria, Broad-finned Galaxias are known to penetrate large distances

inland and upstream to high altitudes. They have been reported to 1625 masl (approx. river

distance inland 400 km) in the upper Snowy River system, reaching to 620 masl in the Deddick

River (approx. river distance inland 170 km), to 360 masl (approx. river distance inland 210 km) in

the Mitchell River system, and to 850 masl (approx. river distance inland 230 km) in Lake Tarli

Karng in the Thomson River basin.

Broad-finned Galaxias is commonly found to 400 masl and above, and should occupy the lower

and mid reaches of the Thomson River system, with small, isolated populations possibly found

higher in the catchment. Broad-finned Galaxias are known to climb moist, vertical barriers by

using their downward facing pectoral and pelvic fins to adhere to substrates using surface tension

(McDowall 2003). Consequently they can be found in small, steep tributaries, and upstream of

waterfalls.

Common Galaxias (Galaxias maculatus)

Common Galaxias adults migrate downstream on the new or full moon, mostly during autumn,

and spawn on spring tides in the upper tidal reaches of estuaries (Benzie 1968, McDowall 1996).

The larvae then go to sea, and migrate back into the freshwater reaches of rivers as juveniles about

six months later, in spring–summer (McDowall 1996).

Common Galaxias have been recorded in the Thomson River as far upstream as Walhalla, where

21 were collected near the bridge on the Walhalla Road in 1988. This is the only known record of

the species in the system upstream of the Horseshoe Bend Tunnel. Common Galaxias have been

recorded, however, at several nearby sites (e.g. Coopers Creek, Bruntons Bridge), but these are all

downstream of the tunnel in surveys since the mid 1980s.

Throughout its range, the Common Galaxias is known to penetrate to high altitudes and large

distances inland. It has been recorded in the Wonnangatta River to 570 masl (approx. river

distance inland 250 km), the Tambo River near Bindi Station to 440 masl (approx. river distance

inland 160 km), the Suggan Buggan River to 370 masl (approx. river distance inland 155 km) and

to 410 masl (approx. river distance inland 165 km) in the Wentworth River.

Common Galaxias are usually found in the lower reaches of river basins, but are common to over

400 masl and could be expected to be found in the upper Thomson River system to above

450 masl, including the Aberfeldy River.

Australian Bass (Macquaria novemaculeata)

Australian Bass adults migrate downstream to estuaries during autumn and winter to spawn, before

returning upstream (Harris 1986). Juveniles migrate upstream in spring–summer. Males mostly

remain in lower tidal waters, while females travel farther upstream (McDowall 1996).

Downstream migration of adults has been linked to flooding (Harris 1986). Most Australian Bass

recorded in the Thomson River were found in the lower reaches around Myrtlebank and Longford.



There are surprisingly few records from the mid reaches to more upland regions of many streams,

considering that females are able to move long distances upstream (e.g. Snowy Falls, approx. 240

km river distance inland). Anecdotal angler reports from other coastal Victorian streams suggest

Australian Bass were once found up to about the mid reaches of many larger systems, to around

300 masl. Consequently, Australian Bass should be found in the Thomson River in the lower and

mid upper reaches, but not extending upstream as far as the Aberfeldy River.

Tupong (Pseudaphritis urvillii)

Tupong undertake downstream migrations to the sea during autumn and winter to spawn,

coinciding with increases in river flow (Koster and Dawson 2009, Crook et al. 2010). Juveniles

migrate upstream into rivers about six months later during spring–summer (Hortle 1979). Males

mostly remain in estuaries, whilst females travel further upstream (Hortle 1979).

Tupong have been recorded in the Thomson River as far upstream as Beardmores Track below the

Thomson Dam wall (290 masl, approx. river distance inland 190 km) and at several other nearby

sites upstream of Horseshoe Bend Tunnel (e.g. The Narrows, Walhalla Road bridge) in various

surveys since the late 1970s. They are more common downstream of Horseshoe Bend Tunnel,

having been recorded at several nearby sites (e.g. Coopers Creek, C5 Track, Bruntons Bridge) in

surveys since the late 1970s (Tunbridge 1997, Koster and Crowther 2003, Koster et al. 2009).

Throughout its range, the Tupong is known to penetrate to high altitudes and large distances

inland, such as the Wonnangatta River to 570 masl (approx. river distance inland 250 km), the

Tambo River north branch to 640 masl (approx. river distance inland 180 km), the Suggan Buggan

River to 690 masl (approx. river distance inland 170 km) and Thirty Mile Creek in the Mitchell

River basin to 890 masl (approx. river distance inland 220 km).

Most Tupong are found in the lower reaches of coastal river systems, but it appears that larger

females are found upstream (Hortle 1979). Consequently, Tupong should be found throughout the

Thomson River catchment, including the upper reaches to about 500 masl, including the Aberfeldy

River.



3 Factors impeding the distribution of Australian Grayling and other diadromous fish in the upper Thomson River system

Thomson Dam

The Thomson Dam has greatly modified the hydrology of the river downstream of the storage

(Gippel and Stewardson 1995, Cottingham et al. 2001, Earth Tech 2003, TMEFT 2004). Changes

to hydrology in the Thomson River most likely impact on the distribution of diadromous fishes

over the length of the river through the loss of important biological cues (e.g. high flows) for fish

migrating into the system or throughout the river (TMEFT 2004). There was also a short period in

1984–85 when hypolimnetic water at 9–11°C was released from the dam. However, a multi-level

offtake has since been used to maintain release water temperatures within target levels specified in

Schedule F5 of the State Environment Protection Policy (Waters of Victoria). Based on limited

data, excluding the period in 1984–85 when hypolimnetic water was released, Gippel et al. (1992)

reported that dam regulation increased mean water temperatures below the dam by around 3°C in

winter and reduced mean water temperatures by 3°C in summer. The reduction in summer water

temperatures persisted downstream to Coopers Creek, but winter temperatures were only increased

by 1°C at The Narrows and not at all at Coopers Creek (Gippel et al. 1992). The presence of the

diadromous Short-finned Eel, Long-finned Eel and lampreys, which are capable of climbing over

barriers, in the Thomson River below the dam nonetheless suggests that suitable migration and

attraction cues (i.e. flows) for fish exist in this reach. The presence of self-sustaining populations

of non-migratory native fish species (e.g. Southern Pygmy Perch Nannoperca australis, River

Blackfish Gadopsis marmoratus, Australian Smelt) in the Thomson River below the dam also

indicates that water temperature and flow are not preventing the establishment of fish populations

in the upper Thomson River and that native fish are able to survive in this reach.

Bushfires

The immediate impacts of fires such as increased water temperature and decreased dissolved

oxygen levels, as well as the associated effects of fires, such as sediment deposition into streams,

can impact fish communities by decreasing pool depth by filling with sediment, reducing food

supply and reducing the useable resting and spawning habitats. Impacts of fire usually decrease

with time as catchments recover and sediment is flushed from the system. The degree of impact of

recent fires (e.g. 2006-07) on fish habitat in the upper Thomson River catchment (and hence the

ability for the catchment to support diverse fish communities) is unknown, but is not considered a

major factor in lack of diadromous fish species in that part of the system. Given that diadromous

fishes in south-eastern Australia typically undertake annual upstream migrations from marine

environments into rivers, and different species migrate at different times, at least some diadromous

fish species should be present at any given time. Even if habitat was extremely unsuitable, small

numbers of fish would be present, replaced by new recruits (Lyon and O’Connor 2008). Surveys

conducted in the Thomson River since the fires have collected Australian Grayling, Tupong and

Common Galaxias at various sites in areas that were burnt (e.g. Coopers Creek, C5 Track,

Bruntons Bridge) (Figure 1), but not from sites upstream of the Horseshoe Bend Tunnel (e.g.

Koster and Dawson 2008, Koster et al. 2009).



Figure 1. Fish survey sites at C5 Track (a) and Bruntons Bridge (b) following the 2006-07 fires.

Horseshoe Bend Tunnel

The Horseshoe Bend Tunnel (Figure 2) on the upper Thomson River has been identified in the

Victorian State Fishway Program as a barrier to fish movement (McGuckin and Bennett 1999).

The length of the Thomson River downstream of the tunnel is approximately 128 km. The length

of river upstream of the tunnel is approximately 22 km to the Thomson Dam and 63 km to and

including the Aberfeldy River. The tunnel (approximately 220 metres in length) was constructed in

1911–12 with most of the river flow diverted through the tunnel and bypassing the one kilometre

reach of the Thomson River known as Horseshoe Bend (LCC 1991). The record of an Australian

Grayling and the records of other diadromous species upstream of the tunnel indicate that some

migratory fish have been able to move upstream, possibly taking advantage of infrequent but

appropriate flows through the old river channel. Opportunities for fish to migrate through the river

channel are extremely limited, however, because flow in the channel is estimated to occur only

about 3% of the time (Koster and Crowther 2003). Overflow into the bend occurs only during high

flow events typically only two to three times per year and usually lasting only for a few days on

each occasion (Koster and Crowther 2003). In contrast, the timeframe over which upstream and

downstream migration of diadromous fishes in south-eastern Australia occurs is far more

extensive, encompassing much of the year, with different species also migrating at different times

of the year, and under varying flow conditions (Koehn and O’Connor 1990).

Migration of fish through the tunnel would also be impeded. Reluctance of fish to move through

tunnels has been reported for a range of fish species (Ahmad et al. 1962, Pavlov 1989). The

Horseshoe Bend Tunnel presents several major impediments to upstream and downstream fish

passage, including steep gradients and sudden drops in height (Figure 1). At the upstream and

downstream ends of the tunnel the surface comprises smooth rock and gradients exceed 15°. Baker

and Boubee (2006) found that juvenile and adult Common Galaxias were unable to pass over

ramps 1.5 m long, sloped at 15° with a bare surface. At the upstream end of the tunnel there is also

a turbulent cascade and large drop (>200 mm) in height. Various studies suggest that juveniles and

adults of Common Galaxias are prevented from moving upstream by vertical drops of only 100

mm and 200 mm respectively (McDowall 2000, Baker 2003). The white water and turbulence at

the upstream end of the tunnel would also disorientate fish and provides no resting areas for

several metres. Boubee et al. (1999) predicted that Common Galaxias had a maximum burst

swimming distance of only 3.3 m at a velocity of 0.70 m/sec, which declined to 2.1 m at 1.0 m/sec.

Water velocities within the tunnel (see below) exceed these values.

In addition to steep gradients and drops in height, the tunnel presents several other impediments to

fish passage. Water velocities within the tunnel have been measured under low flow conditions

(a) (b)



(240 ML/day) and range from 1.2 to 2.5 m/sec (Thiess Environmental, unpublished data). For a

high flow period (1682 ML/day), data modelling indicates water velocities of approximately

6.2 m/sec in the tunnel (Snowy Mountains Engineering Corporation, unpublished data). This range

of velocities (1.2–6.2 m/sec) is known to far exceed the swimming capabilities of small

diadromous fishes (Saddlier and O’Connor 1997, Boubee et al. 1999). Saddlier and O’Connor

(1997) found that juvenile Tupong were unable to negotiate an artificial channel 2 m long at

velocities ranging from 1.1–1.9 m/sec, although some larger fish (190–200 mm in length) could

negotiate the channel. The ability of Common Galaxias to negotiate the channel at velocities

greater than 1.0 m/sec was also severely reduced, with a 90% failure rate (Saddlier and O’Connor

1997).

Natural light within the tunnel is also severely reduced, which can be a behavioural impediment to

fish movement (O’Brien 1999, Thorncraft and Harris 200l0, Fairfull and Witheridge 2003). Recent

research has shown that the upstream movement of a range of small native Australian fishes

(Australian smelt, unspecked hardyhead Craterocephalus fulvus, bony herring Nematalosa erebi,

carp gudgeon Hypseleotris spp.) is adversely impacted by low light intensity (Jones in prep).

Several recent studies have also shown that the upstream migration of diadromous galaxiids

(e.g. Common Galaxias, Spotted Galaxias Galaxias truttaceus) through fishways occurs

predominantly during daylight (Morgan and Beatty 2006, Zampatti et al. in prep). The installation

of ‘windows’ (e.g. steel grating) within barriers such as road culverts to provide light is

increasingly incorporated into fish passage improvement works (e.g. Cumberland River at Lorne,

Tahbilk Lagoon at Nagambie) in recognition that many species require natural daylight patterns

for movement and that darkened areas such as tunnels and culverts create behavioural barriers

(Thorncraft and Harris 2000).

Although other potential obstacles to fish movement exist in the upper Thomson River (e.g. rapids

at Bruntons Bridge, The Gorge), the physical and hydraulic complexity of these natural structures

produces low velocity resting areas and reduces the distances travelled between rests at high

velocities, thereby enabling the successful upstream passage of fish. In addition, during high flows

rapids are ‘drowned’, which also provides important opportunities for fish to move around any

obstacles to movement (Baker 2003).

Figure 2. Upstream (a) and downstream (b) ends of the Horseshoe Bend Tunnel and (c) old river

channel.

(a) (b) (c)



4 Restoring connectivity of fish passage for Australian Grayling and other diadromous fish in the upper Thomson River system

Native fish species


Thomson River will enable diadromous fish species, including the nationally threatened Australian

Grayling, to move into large areas of habitat upstream. Australian Grayling has declined in

distribution and abundance throughout its range due to factors such as barriers to movement and

habitat loss and degradation (Backhouse et al. 2008, DEWHAC 2010). A National Recovery Plan

for Australian Grayling has been developed by an expert panel to address these threats and

includes as a key recovery objective increasing the length of rivers available by facilitating fish

passage past barriers (Backhouse et al. 2008). Improved access for Australian Grayling and other

diadromous fish would be available to a further 22 km of the Thomson River upstream to the

Thomson Dam, 63 km of the Aberfeldy River, and numerous tributary streams, including streams

in the Baw Baw National Park. It is recognised that the Thomson Dam will continue to restrict

diadromous fish distribution upstream of the dam wall. Nonetheless, a substantial increase in the

opportunities for diadromous fish to access the upper reaches of the system will be achieved

through restoring fish passage past the tunnel, which supports the need to restore access to rivers

for Australian Grayling in accordance with the national recovery plan for the species, and

represents an important step toward restoring connectivity and biodiversity of native fish

communities in the Thomson River system.

The extent to which fish would use the upper Thomson River, or tributaries such as the Aberfeldy

River, following the reinstatement of fish passage around Horseshoe Bend Tunnel would depend

on a complex range of factors such as flow and habitat conditions, which are likely to vary

considerably through time. In the upper Thomson River system, flow in the Thomson River

generally exceeds flow in the Aberfeldy River, which might encourage more fish to continue

migrating up the Thomson River. On the other hand, the unregulated Aberfeldy River which has a

more natural flow regime, generally comprises a large proportion of flow in the upper Thomson

River system during high flow periods (i.e. spring – early summer), which represents the key

upstream migration period for diadromous fishes in south-eastern Australia (Koehn and O’Connor

1990). The presence of the diadromous Short-finned Eel in the upper Thomson and Aberfeldy

rivers is evidence of the upstream colonisation of both stream systems, and also suggests that

suitable migration and attraction cues (i.e. flows) exist in both rivers.

Alien fish species

Two alien fish species — Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss)

— have been recorded in the upper Thomson River system. Trout have been implicated in the

decline of native fishes worldwide, including galaxiids and Australian Grayling (Crowl et al. 1992,

McDowall 2006). Trout are widespread in the Thomson River, including upstream and

downstream of Horseshoe Bend Tunnel. As they are already found upstream and downstream of

the tunnel, the reinstatement of flows around the tunnel would not result in a range expansion of

either species. Allowing additional native fish species upstream into waters containing alien

species may increase predatory or competitive interactions, though often the degree of interaction

is related to habitat complexity and fish density. Another two alien species, Common Carp

(Cyprinus carpio) and Redfin Perch (Perca fluviatilis), are restricted to the mid to lower reaches of

the Thomson River around Cowwarr. Habitat conditions in the upper Thomson system (i.e. fast

flowing riffle/run habitats) are not considered favourable to the establishment of these species,



though some individuals may penetrate further upstream. The positive benefits of allowing native

diadromous fish species access to a relatively large expanse of upstream habitat, including smaller

tributary streams, out-weighs any possible negative impacts from alien species.

Timing of fish movement

The upstream migratory period of diadromous fishes in south-eastern Australia encompasses an

extensive time frame (Koehn and O’Connor 1990), although the migration of different species

from marine habitats into lower freshwater reaches of rivers is concentrated around late spring –

early summer (Sloane 1984, Gehrke et al. 2002, Raadik et al. 2001, Zampatti et al. 2003). In the

Thomson River, fish must first migrate various distances within the Gippsland Lakes, then up the

Latrobe River system before they enter the Thomson River itself, before moving upstream through

the lowland section to the gorge section commencing at Cowwarr Weir. During migration over this

distance, some species may move at different speeds and some movements may be continuous or

erratic, so the timing of diadromous fishes reaching the upper Thomson River system upstream of

Cowwarr Weir is unclear.

Environmental flow recommendations have been developed for the Thomson River which include

providing flows for fish passage (Earth Tech 2003, TMEFT 2004). In particular, low flow freshes

have been recommended in the period December to April to provide localised fish movement in

the upper reaches. A continuous low flow has also been recommended between December to April

(Earth Tech 2003, TMEFT 2004). Given the uncertainty about the timing of diadromous fishes

reaching the upper reaches, a continuous low flow along the channel of the Thomson River around

the Horseshoe Bend Tunnel for upstream fish migration may be more effective in facilitating

upstream fish passage than short-duration peak flows. The flows provided need to be of sufficient

depth to allow for localised fish passage but also to provide refuge. A depth of >0.4 m has been

recommended in the environmental flows determination for the Thomson River (Earth Tech 2003)

as being the minimum water depth for fish habitat.

Recent research has shown that adult Australian Grayling undertake downstream spawning

migrations to the lower reaches of rivers around April–May, coinciding with rises in flow or

‘freshes’, followed by return upstream migrations (Koster and Dawson 2010a, b). Similarly, adult

Tupong migrate downstream to the sea for spawning around May–August, coinciding with

relatively high flows (Koster and Dawson 2009, Crook et al. 2010). Providing freshes is therefore

recommended during April–August to facilitate the downstream (and return upstream) migration

of some adult diadromous species. High flow freshes (i.e. >800 ML/d) have been recommended in

the period May–November as part of the environmental flow recommendations for the Thomson

River (Earth Tech 2003, TMEFT 2004).

Regulating flow through Horseshoe Bend Tunnel

Flow rates are one of the important factors limiting the upstream movement of fish. Although flow

rates through the tunnel could be reduced, there are other impediments to fish movement through

the tunnel, such as steep gradients, sudden drops in height and lack of light. Consequently, altering

flow rates alone would have little effect on fish migration. In contrast, the natural river channel of

the Thomson River around Horseshoe Bend provides greater opportunities for fish movement

because of the complexity of flow patterns (riffle, run, pool, glide, etc.) which provide

opportunities for fish to move over short or long distances at a time, aswell as areas of useable

resting and foraging habitat.



Fish stocking

The recruitment of diadromous fishes relies on complex migrations from freshwater environments

to the sea and vice versa. Given that most diadromous fish species in the Thomson River are only

short-lived (e.g. Australian Grayling: 2–5 years, Common Galaxias: 1–2 years), if diadromous fish

species such as Australian Grayling were irregularly stocked upstream of the tunnel they would

persist for only a short period and would not be able to develop self-sustaining populations in the

upper reaches unless the critical migration pathway between fresh water and the sea was restored.



5 Conclusions and recommendations

The results of this review indicate that Australian Grayling and most other diadromous fish species

in the Thomson River system are confined to the lower and mid reaches, but would naturally also

be found in the upper reaches of the system if they had access. The presence in the upper Thomson

River system of the diadromous Short-finned Eel, Long-finned Eel and lampreys, which are

capable of climbing over barriers, suggests that suitable migration/attraction cues (i.e. flows) exist

in the upper reaches. The presence of self-sustaining populations of non-migratory native fish

species also indicates that water temperature and flow are not preventing the establishment of fish

populations in the upper Thomson River and that native fish are able to survive in this reach.

A major barrier to fish passage into the upper reaches of the Thomson River systems is the

Horseshoe Bend Tunnel. Opportunities for fish to migrate through the old river channel are

limited, with flow in the channel estimated to occur only about 3% of the time. Migration of fish

through the tunnel would also be impeded by steep gradients, sudden drops in height and excessive

water velocities. A lack of natural light in the tunnel poses a further impediment to fish passage.


Thomson River will enable diadromous fish species, including the nationally threatened Australian

Grayling, to move into large areas of habitat upstream.

The following recommendations are made based on the findings of this study:

• Restore fish passage connectivity along the old course of the Thomson River around

Horseshoe Bend Tunnel. The environmental flow recommendations developed for the

Thomson River should be used as a basis for determining the flows required for fish passage.

Given the extended migratory period and uncertainty about the exact timing of diadromous

fishes reaching the upper Thomson River system, providing a continuous low flow for fish

migration may be more effective in facilitating upstream fish passage than short-duration peak

flow events. Providing ‘freshes’ is recommended during April–August to facilitate the

downstream (and upstream return) migration of adult diadromous species, although for

Australian Grayling the key period for adult migration is April–May. It is recommended that

the environmental flow recommendations developed for the Thomson River be used as a

guide for water depth (e.g. > 40 cm).

• Design and implement a long-term monitoring program to assess the re-establishment of

diadromous fishes. This should include pre-intervention and post-intervention monitoring in

the upper Thomson River, Aberfeldy River, tributaries, and the mid reaches of the Thomson

River near Cowwarr, to provide an indication of fish migration into the system.



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Documents

W. Koster and T.A. Raadik - West Gippsland...Migratory freshwater fish comprise about 70% of the native freshwater fish fauna of the coastal-draining Thomson River system in West Gippsland