Scientific Advisory Committee (SAC)Scientific Advisory Committee (SAC)Sub-Committee on Stock Asssessment (SCSA)Sub-Committee on Stock Asssessment (SCSA)

Working Group on Demersal SpeciesWorking Group on Demersal SpeciesIzmir, Turkey, 15-19 September, 2008Izmir, Turkey, 15-19 September, 2008

Stock assessment of hake in GSAs 15 and 16

F. Fiorentino, M. Dimeck, M.T. Spedicato, A. Abella, P. Accadia, V. Gancitano

The aim of this paper is:

• To compare assessments of hake done with different approaches and data deriving from indirect (fisheries monitoring) and direct (scientific surveys) sources in the investigated area;

• To evaluate the use of different biological reference points in order to recommend fishery advices.

Hake yield by trawling - GSA 16

0

500

1000

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2001 2002 2003 2004 2005 2006 2007 2008

Tons

DTS

Hake trawl surveys - GSA 16

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60

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BI (k

g/km

2)

GRUND MEDITS

The yield and abundance in GSA 16……

Hake Historical landing Hake Malta

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25

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Year

Lan

ding

s (t)

Landing data from GSA 15

GSA 15 Hake Biomass Index

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60

2002 2003 2004 2005 2006 2007

Year

BI (k

g/km2 )

MEDITS surveys

y = 0.5276x + 21.018R2 = 0.3349

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60

0.00 10.00 20.00 30.00 40.00 50.00 60.00

GSA 16 BI

GSA

15

BI

An attempt of VPA under steady state assumptions with landings information of 2006 and 2007 in GSA 16

by winVITwinVIT package

  Females Males Total

Observed Yield (tons) ……  ……..  1598 

Reconstructed Yield (tons) 796 802 1597

Recruits at 12 cm TL (millions) 13.5 21.2 34.7

Mean Z 0.659 0.859  

Mean F 0.319 0.429  

Global F 0.656 0.690  

Catch mean length (cm) 21.1 19.9  

Stock mean length (cm) 21.1 17.7  

Catch and fishing mortality by size of hake (F & M) Catch and fishing mortality by size of hake (F & M) Mean Yield and LDF of landings of 2006 and 2007 _GSA 16Mean Yield and LDF of landings of 2006 and 2007 _GSA 16

by winVIT Package and scalar M by winVIT Package and scalar M

0

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1000

1500

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3000

10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74

00.20.40.60.811.21.41.61.82

number_f number_m Z_f F_f Z_m F_m

Num

ber (

thou

sand

)M

ortality

TL(cm)

Y/R and SSB/R analysis vs Factor of current fishing mortalityY/R and SSB/R analysis vs Factor of current fishing mortalityof hake (F & M) with winVIT Package. of hake (F & M) with winVIT Package.

010

2030

4050

6070

80

0 0.10.20.30.40.50.60.70.80.91 1.11.21.31.41.51.61.71.81.92 0

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Y/R_m Y/R_f SSB_m SSB_f Factor of Fc

gram

s

Current status

Sex Status Factor Y/R B/R SSB

Females

F(Virgin) 0 0 1390.592 1112.604

F(0.1) 0.38 65.425 502.741 353.431

F(Max) 0.54 67.996 346.98 228.03

F(Current) 1.01 58.968 123.609 60.647

F(Double) 2 40.406 29.036 4.488

Males

F(Virgin) 0 0 424.559 315.641

F(0.1) 0.40 38.298 130.879 73.994

F(Max) 0.62 40.201 80.884 37.028

F(Current) 1.01 37.827 42.41 12.124

F(Double) 2 30.887 19.528 2.109

Diagnosis from winVIT package……..

…overfishing…

Y/R and SSB/R analysis vs Factor of current fishing mortalityY/R and SSB/R analysis vs Factor of current fishing mortalityof hake (F & M) with Yield Package. of hake (F & M) with Yield Package.

GSA 15 & 16GSA 15 & 16

Yield per recruit according to Yield package - Hake female Gsa 15 & 16

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Fishing mortality

Y/R

in k

g

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1.5

2

2.5

Main BRPs obtained by Yield packageMain BRPs obtained by Yield package for hake in GSA 15 & 16 for hake in GSA 15 & 16

 Yield based RP female male  F based RP female male

Y/Rmax59.6  39.8

Fmax0.244  0.315

Y/RF0.157.4  37.4

F0.10.157 0.194 

Y/RSPR_0.3559.5  37.8 

FSPR_0.350.154  0.202 

Diagnosis from Yield package……..

Fishing mortalities from MEDITS dataHake - combined sex - GSA 15 & 16

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1.4

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2008F

GSA 16 GSA 15

….and Surba analysis……

What is the current exploitation of hake?

According to the Y/R and trawl surveys mortalities … the stock is ….overfished………

and to reach a target such as F0.1….. the reduction of current F should be of about 60%

Method F RemarksB & H estimator on MEDITS data2005-2006-2007

0.76 Minimum length of fully recruitment (L’) of 18 cm TL (Females)

Surba on MEDITS data Mean of 2005 and 2006

0.70 Mean of age class 1-4 (Combined sex)

Merluzzo (2004-2007)

0255075

100125150175200225250275300

Catture Aladym Sbarchi Irepa

Other analythical approaches…The recostruction of hake landings fin the GSA 16 by ALADYM Model………..

Biomass of hake - GSA16

010002000300040005000600070008000

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tons

reduce capacitytraw ling banmesh sizecombined measuresStatus quo

Some management scenarios for GSA 16 based on ALADYM model…………..

Yield of Hake - GSA16

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tons

reduce capacitytraw ling banmesh sizecombined measuresstatus quo

ESSB/USSB Hake - GSA16

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0.16

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ratio

reduce capacitytraw ling banmesh sizecombined measuresstatus quo

What about the stock status according to “global” What about the stock status according to “global” approaches?approaches?

Equilibrium composite biomass dynamic models       

Zmbp= 1.161459 =0.5*(Boo/b')

       

MBP'= 31.56166 MBP=K/2*Zmbp

       

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0 0.10.20.30.40.50.60.70.80.91 1.11.21.31.41.51.61.71.81.92 2.12.22.32.42.5

Z

Biol

ogic

al P

rodu

ctio

n (k

g p

er k

m2 )

Electronic sheet by A. Abella

Non equilibrium biomass dynamic models

Electronic sheet by A. Abella

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.0050.00

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B

Predicted

Observed B

Biological Production and recent evolution (diamonds)

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510

1520

2530

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4550

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Z

BP

Approach Data Period Current point

Reference point Diagnosis

VIT Biological samplings of

landings

2006-2007 F*=0.66

(Females)

Fmax =F*× 0.54=0.35F0.1 =F*×0.38=0.25

O; -46%O; -62%

Yield & Surba Trawl surveys

2005-2006

F=0.70(combine

d sex)

Fmax= 0.24F0.1= 0.16

FSPR=0.3= 0.15O; -55%O; -71%

Yield & B_H estimator

Trawl surveys

2005-2007 F=0.76

(Females)

Fmax= 0.24F0.1= 0.16

FSPR=0.3= 0.15O; -65%O; -78%

Surplus Production Composite

Trawl surveys

2005-2006

Z=1.18(combine

d sex)

ZMBP (Schaefer)=1.16ZMBP (Fox)=0.89

EO

Non –equilibrium

Surplus production

Trawl surveys

2005-2006

Z=1.18(combine

d sex)

ZMBP = 0.87FMBP = 0.39

OO; -44%

Recommendation – reduce fishing mortality at least of 44%