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GIANNOULAKI M., SOMARAKIS S., MACHIAS A., SIAPATIS A., PAPACONSTANTINOU C.
Hellenic Centre for Marine Research, PO Box 2214, Iraklion 71003, GreeceDepartment of Biology, University of Crete, PO Box 2208, 41409 Voutes,
Iraklion, Greece
GFCM – Izmir 2008GFCM – Izmir 2008
Stock assessment of the Aegean Sea (GSA 22) Anchovy and Sardine stock by Integrated Catch at
age analysis (ICA)
An Integrated Catch-at-Age analysisAn Integrated Catch-at-Age analysis
was applied based on commercial catch data (2000-2006) was applied based on commercial catch data (2000-2006)
andand tuning indices: the biomass estimates from acoustic surveys and tuning indices: the biomass estimates from acoustic surveys and
Daily Egg Production Method (DEPM) estimates (2003-2006) Daily Egg Production Method (DEPM) estimates (2003-2006)
method that standard VPA assessments are tuned with method that standard VPA assessments are tuned with results from fishery independent stock assessment results from fishery independent stock assessment techniques (Patterson & Melvin 1996). techniques (Patterson & Melvin 1996).
GFCM – Izmir 2008GFCM – Izmir 2008
The FisheryThe Fishery
Purse seine fleetPurse seine fleet
No purse
seines
Gross Tonnage (GT*)
Horse Power
(kW)
Mean fleet age
Average length
Greece 291 11.626 52.038 25 19
GFCM – IzmirGFCM – Izmir 20082008
>95% responsible for anchovy and sardine catches in Greek waters
Technical measures: Fishing practices, fishing seasons Technical measures: Fishing practices, fishing seasons & areas, effort, gear regulations& areas, effort, gear regulations
Closed period (mid December – end of February)Closed period (mid December – end of February) Minimum distance from shore 300m or 30m bottom depthMinimum distance from shore 300m or 30m bottom depth Minimum no of lamps per vessel (6)Minimum no of lamps per vessel (6) Min landing size (anchovy: 9 cm, sardine: 11 cm)Min landing size (anchovy: 9 cm, sardine: 11 cm) Min mesh size (40 mm for purse seines working daytime, Min mesh size (40 mm for purse seines working daytime,
14 mm for purse seines working nighttime)14 mm for purse seines working nighttime)
GFCM – Izmir GFCM – Izmir 20082008
Data usedData used
Purse seine fishery in North Aegean Sea (main Purse seine fishery in North Aegean Sea (main fishing grounds for anchovy and sardine in fishing grounds for anchovy and sardine in Aegean Sea)Aegean Sea)
Annual anchovy and sardine landingsAnnual anchovy and sardine landings 2000-20062000-2006 HCMR data collection system, several national & HCMR data collection system, several national &
EU projects of HCMR & FRIEU projects of HCMR & FRI Data from 2003 onward were collected within the Data from 2003 onward were collected within the
framework of the framework of the Greek National Fisheries Data Greek National Fisheries Data Collection programCollection program
GFCM – IzmirGFCM – Izmir 20082008
DataData
Data were collected on a seasonal basisData were collected on a seasonal basis Measurements: Total length, biological sampling Measurements: Total length, biological sampling
(weight, otoliths: age reading, gonads for maturity (weight, otoliths: age reading, gonads for maturity estimates)estimates) Age sampling: Age sampling:
separate length and age sampling or separate length and age sampling or representative age sampling. representative age sampling.
Landings were grouped by length classes (1 Landings were grouped by length classes (1 cm) and applied on a yearly basis to ALK.cm) and applied on a yearly basis to ALK.
GFCM – Izmir GFCM – Izmir 20082008
Biological information used as input for the model:Biological information used as input for the model:
Maturity-at-age:Maturity-at-age: based on biological samples based on biological samples from commercial and research vessels from commercial and research vessels collected during the spawning seasoncollected during the spawning season
Natural mortalityNatural mortality: fixed parameter over years : fixed parameter over years and ages (M=0.7 anchovy, M=0.8 for sardine, and ages (M=0.7 anchovy, M=0.8 for sardine, based on acoustic estimates (No ind/ age based on acoustic estimates (No ind/ age group) group)
Reference age for the fishery Reference age for the fishery age group 2 age group 2 (fully exploited & fully recruited)(fully exploited & fully recruited)
GFCM – IzmirGFCM – Izmir 20082008
Weighting factors regarding catchesWeighting factors regarding catches
Ages 0 and 4 were downweighted (0.01), considered Ages 0 and 4 were downweighted (0.01), considered marginal marginal in terms of their percentage in the catch in terms of their percentage in the catch (< (< 5% and 1% respectively)5% and 1% respectively)
Age 3 was downweighted (0.3) represented 6% in the Age 3 was downweighted (0.3) represented 6% in the catchcatch
Six years separable constrainSix years separable constrain Reference age for the fishery Reference age for the fishery age group 2 age group 2 (fully (fully
exploited & fully recruited)exploited & fully recruited) Mean F Mean F for agesfor ages 1 to 3+ 1 to 3+ was estimatedwas estimated
GFCM – IzmirGFCM – Izmir 20082008
Total anchovy landings
R2 = 0.8481
0
5000
10000
15000
20000
25000
2000 2001 2002 2003 2004 2005 2006
Year
Ca
tch
es
(t)
GFCM – IzmirGFCM – Izmir 20082008
Anchovy
GFCM – IzmirGFCM – Izmir 20082008
Total sardine landings
R2 = 0.2186
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2000 2001 2002 2003 2004 2005 2006
Year
Ca
tch
es
(t)
Sardine
Tuning indicesTuning indices(fishery independent surveys)(fishery independent surveys)
38o
39o
40o
41o
22o 23o 24o 25o 26o
Thermaikos Gulf
38o
39o
40o
41o
22o 23o 24o 25o 26o
Thermaikos Gulf
GFCM – IzmirGFCM – Izmir 20082008
1
51
101
151
201
251
301
351
401
451
501
551
601
651
701
39.00
40.00
41.00
23.00 24.00 25.00 26.00
Total Biomass (acoustics)Total Biomass (acoustics) Stock Spawning biomass (DEPM)Stock Spawning biomass (DEPM)
Anchovy
0
10000
20000
30000
40000
50000
60000
70000
80000
2003 2004 2005 2006
Bio
ma
ss
(t)
Acoustics TSB DEPM SSB
GFCM – IzmirGFCM – Izmir 20082008
Tuning indicesTuning indices(fishery independent surveys)(fishery independent surveys)
38o
39o
40o
41o
22o 23o 24o 25o 26o
Thermaikos Gulf
38o
39o
40o
41o
22o 23o 24o 25o 26o
Thermaikos Gulf
Total Biomass (acoustics)Total Biomass (acoustics)
Sardine
Acoustics TSB
0
10000
20000
30000
40000
50000
60000
2003 2004 2005 2006
Bio
mas
s (t
)
Anchovy population structure per age group
0
1000000
2000000
3000000
4000000
5000000
6000000
2003 2004 2005 2006Year
No
of
fis
h in
th
ou
sa
nd
s
Age1
Age2
Age3+
Population statusPopulation status
GFCM – IzmirGFCM – Izmir 20082008
Major component of the stock:
1-year-old and 2-year-old fish
Sardine population structure per age group
0
200000
400000
600000
800000
1000000
1200000
2003 2004 2005 2006Year
No
of
fis
h in
th
ou
sa
nd
s
Age1
Age2
Age3+
Length frequency distribution…Length frequency distribution…
2 sub-areas: 2 sub-areas: East areaEast area (Thracian Sea (Thracian Sea
and Strymonikos Gulf) and Strymonikos Gulf) Shift towards smaller length Shift towards smaller length
classes in 2005 & 2006classes in 2005 & 2006
West areaWest area (Thermaikos (Thermaikos and Evoikos Gulfs)and Evoikos Gulfs) Shift towards smaller length Shift towards smaller length
classes in 2005 & 2006classes in 2005 & 2006
Anchovy
East Area
0
5
10
15
20
25
30
35
52.5
62.5
72.5
82.5
92.5
102.5
112.5
122.5
132.5
142.5
152.5
162.5
172.5
182.5
%
2003
2004
2005
2006
West Area
0
5
10
15
20
25
30
35
52.5
62.5
72.5
82.5
92.5
102.5
112.5
122.5
132.5
142.5
152.5
162.5
172.5
182.5
Length (mm)
%
GFCM – IzmirGFCM – Izmir 20082008
(population)
Length frequency distribution…Length frequency distribution…
Sardine
East Area
0
5
10
15
20
25
30
35
40
45
52.5 67.5 82.5 97.5 112.5 127.5 142.5 157.5 172.5 187.5
%
2003
2004
2005
2006
West Area
0
5
10
15
20
25
30
35
40
45
52.5 67.5 82.5 97.5 112.5 127.5 142.5 157.5 172.5 187.5
Length (mm)
%
2 sub-areas: 2 sub-areas: East areaEast area (Thracian Sea (Thracian Sea
and Strymonikos Gulf)and Strymonikos Gulf) Shift towards bigger length Shift towards bigger length
classes in 2003 & 2006classes in 2003 & 2006
West areaWest area (Thermaikos and (Thermaikos and
Evoikos Gulfs)Evoikos Gulfs) Shift towards bigger length Shift towards bigger length
classes in 2006classes in 2006
GFCM – IzmirGFCM – Izmir 20082008
(population)
GFCM – IzmirGFCM – Izmir 20082008
Anchovy Assessment Model: DEPM Absolute_Acoustic Anchovy Assessment Model: DEPM Absolute_Acoustic Linear according to WGMHSA 2005 suggestionLinear according to WGMHSA 2005 suggestion
Age Residuals
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
0 1 2 3 4
Age
Mar
gin
al T
ota
l
Year Residuals
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
2003 2004 2005 2006
Year
Mar
gin
al T
ota
l
GFCM – IzmirGFCM – Izmir 20082008
Anchovy Assessment Model results (DEPM Anchovy Assessment Model results (DEPM Absolute_Acoustic Linear according to WGMHSA Absolute_Acoustic Linear according to WGMHSA 2005 suggestion)2005 suggestion)
Population Population statusstatusStock size
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
500000
2000 2001 2002 2003 2004 2005 2006
Year
Bio
mas
s
Total Spawning
Recruitment
0
5000000
10000000
15000000
20000000
2000 2001 2002 2003 2004 2005
Year
Rec
ruit
s
GFCM – IzmirGFCM – Izmir 20082008
Fishing Mortality
0
1
2
3
2000 2001 2002 2003 2004 2005 2006
Year
Ref
eren
ce F
Fishing mortality
0
0.2
0.4
0.6
0.8
2000 2001 2002 2003 2004 2005 2006
Year
Mea
n F
Exploitation rate
0
0.2
0.4
0.6
2000 2001 2002 2003 2004 2005 2006
Year
F/Z
Aegean anchovy stock
Reference point
Fishing mortality remains more or less at the same level
Exploitation rate < 0.4 since 2003
ResultsResults
Preliminary resultsPreliminary results because of small time because of small time seriesseries
Stock characterized by intermediate Stock characterized by intermediate abundances, abundances, fully exploitedfully exploited, with high fishing , with high fishing mortality ratesmortality rates
Exploitation rate Exploitation rate belowbelow the empirical level the empirical level for stock declinefor stock decline (0.4, Patterson 1992). (0.4, Patterson 1992).
Signs of recovery regarding Signs of recovery regarding E,E, SSBSSB and and RecruitmentRecruitment in 2006 in 2006
Reference pointsReference points can only can only cautionarycautionary suggested assuggested as TBlim=31800 t (CV=0.109), estimated in 2005.TBlim=31800 t (CV=0.109), estimated in 2005. SSBlim=20500 t (CV=0.170), estimated in 2005.SSBlim=20500 t (CV=0.170), estimated in 2005. SSBpa=30750 t (as SSBlim*1.5)SSBpa=30750 t (as SSBlim*1.5)
GFCM – IzmirGFCM – Izmir 20082008
GFCM – IzmirGFCM – Izmir 20082008
Sardine Assessment Model: Acoustic LinearSardine Assessment Model: Acoustic Linear
Year Residuals
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
2003 2004 2005 2006
Year
Mar
gin
al T
ota
l
Age Residuals
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 1 2 3 4
Age
Mar
gin
al T
ota
l
GFCM – IzmirGFCM – Izmir 20082008
Population Population statusstatus
Sardine Assessment Model results (Acoustic Linear Sardine Assessment Model results (Acoustic Linear according to WGMHSA 2005 suggestion)according to WGMHSA 2005 suggestion)
Recruitment
0
2000000
4000000
6000000
2000 2001 2002 2003 2004 2005 2006
Year
Re
cru
its
Stock size
0
10000
20000
30000
40000
50000
60000
70000
80000
2000 2001 2002 2003 2004 2005 2006
Year
Bio
mas
s
Total Spawning
GFCM – IzmirGFCM – Izmir 20082008
Fage-2 remains more or less at the same level
Mean F1-3 shows decreasing trend
Exploitation rate > 0.4
Exploitation rate
0
0.2
0.4
0.6
0.8
2000 2001 2002 2003 2004 2005 2006
Year
F/Z
Aegean sardine stock
Reference point
Fishing mortality
0
0.3
0.6
0.9
1.2
1.5
2000 2001 2002 2003 2004 2005 2006
Year
Mea
n F
Fishing Mortality
0
1
2
3
4
5
6
2000 2001 2002 2003 2004 2005 2006
Year
Re
fere
nc
e F
GFCM – IzmirGFCM – Izmir 20082008
ResultsResults
Preliminary resultsPreliminary results because of small time series because of small time series Stock characterized by intermediate abundances, Stock characterized by intermediate abundances,
fully exploitedfully exploited, with high fishing mortality rates, with high fishing mortality rates Exploitation rate Exploitation rate aboveabove the empirical level for the empirical level for
stock declinestock decline (0.4, Patterson 1992) (0.4, Patterson 1992) Signs of recovery regarding Signs of recovery regarding TBTB and and RecruitmentRecruitment
in 2006in 2006 Reference pointsReference points can only can only cautionarycautionary
suggested assuggested as TBlim=13800 t (CV=0.354), estimated in 2004.TBlim=13800 t (CV=0.354), estimated in 2004.
Management suggestionsManagement suggestions
Small pelagics abundances and recruitment are highly Small pelagics abundances and recruitment are highly variable due to environmental conditionsvariable due to environmental conditions
So,So, Monitoring through fishery independent surveysMonitoring through fishery independent surveys Not increase fishing effortNot increase fishing effort
Shift of the closed periodShift of the closed period (present: mid December (present: mid December to end of February) towards the post recruitment to end of February) towards the post recruitment period of anchovy (e.g. October to December) or period of anchovy (e.g. October to December) or the post recruitment period of sardine (e.g. the post recruitment period of sardine (e.g. February to April)February to April)
GFCM – IzmirGFCM – Izmir 20082008