The Gulf of Maine stock of Atlantic cod

Draft PresentationFor Peer Review Only.

Does not represent final NOAA Decision/Policy.

4/29/08

Description and history of current approach.

The most recent peer review occurred at SAW 31 in 2001 (Mayo et al. 2002). Since then updated assessments were reviewed at GARMI (2002) and GARMII (2005) Mayo and Col (2006).

The VPA is calibrated using the Adapt method (Parrack1986, Gavaris 1988, Conser and Powers 1990).

= 0.23FMSY

= 82, 830 mtSSBMSY

= 16,600 mtMSYMSY-based Reference Points (NEFSC 2002)

= 0.36F20%

= 0.27Fmax

= 0.15F 0.1

Yield and SSB per Recruit-based Reference Points

Status of Gulf of Maine Cod from the 2005 GARM II

Gulf of Maine cod spawning stock biomass has increased since the late 1990s from 11,100 mt in 1997 to 20,500 mt in 2004, but the stock remains low relative to SSBMSY (82,830 mt).

Fully recruited fishing mortality declined to about 0.35 in 2000 and 2001, but has since increased to 0.58 in 2004, indicating that F continues to remain very high relative to fully recruited F reference points (F0.1 = 0.15; Fmsy = 0.23; Fmax = 0.27).

Thus, the stock remains in an overfished condition and overfishing continues to occur.

Commercial Statistical Areas Used to Define theStocks of Atlantic Cod

Figure 5. Strata sampled by the Massachusetts DMF inshore bottom trawl survey.

Gulf of Maine CodTotal Commercial Landings

Year

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Met

ric T

ons

(live

wei

ght)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Figure F1. Total commercial landings of Gulf of Maine cod (NAFO Div. 5Y), 1893-2006.

Gulf of Maine CodNEFSC Spring and Autumn Biomass Indices

Year

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Stra

tifie

d M

ean

Wei

ght (

kg) p

er T

ow

0

5

10

15

20

25

30

Spring SurveysAutumn Surveys

Figure F4. Biomass indices (stratified mean weight per tow) for Gulf of Maine cod from NEFSC autumn bottom trawl surveys.

Gulf of Maine Cod Autumn Survey Indices by Age

Age (years)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Year

1970

1975

1980

1985

1990

1995

2000

2005

+

NEFSC Autumn Survey: Yearclass Strength at Age 1

Yearclass

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Age

1 M

ean

Num

ber p

er T

ow

0

1

2

3

4

5

6

Age 1

NEFSC Autumn Survey: Yearclass Strength at Age 2

Yearclass

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Age

2 M

ean

Num

ber p

er T

ow

0

1

2

3

4

5

6

Age 2

Figure F6. Recruitment indices at age 1 and 2 for Gulf of Maine cod from NEFSC autumn bottom trawl surveys.

GoM Cod - females

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1975 1980 1985 1990 1995 2000 2005

year

prop

ortio

n

age 2

age3

age 4

GoM Cod - females

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1975 1980 1985 1990 1995 2000 2005

year

prop

ortio

n

age 5

age 6

age 7

female - A50 with 95% CI

-1

0

1

2

3

4

5

6

7

1975 1980 1985 1990 1995 2000 2005 2010

Assessment Results

Trends in Average Fully Recruited F (Ages 4-5) and SSB

Residual Pattern from NEFSC Surveys

SpringSurveys

AutumnSurveys

Residual Patterns from MADMF Surveys

Spring andAutumnSurveys

Retrospective Analysis of Fully Recruited F (Ages 4-5)

Retrospective Analysis of Spawning Stock Biomass

A Digression: Split Survey Series

GoM Cod Retrospective Analysis – Combined Series

GoM Cod Retrospective Analysis – Split Series

GoM Cod Retrospective Analysis – Combined Series

GoM Cod Retrospective Analysis – Split Series

GoM Cod Retrospective Analysis – Combined Series

GoM Cod Retrospective Analysis – Split Series

GoM Cod Retrospective Analysis – Combined Series

GoM Cod Retrospective Analysis – Split Series

Back to the Main Feature

Gulf of Maine Cod Average F 4-5

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

single logistic

double logistic

VPA

Comparison between ASAP and VPA ResultsAverage F on Ages 4-5

ASAP Retrospective Pattern – Avg F (Ages 4-5) Single Logistic

ASAP Retrospective Pattern – Avg F (Ages 4-5) Double Logistic

Reference Point Calculations

2 Scenarios

1. Parametric Approach

Fit a stock Recruitment Relationship using estimatesof SSB and Recruits from VPA

Incorporate recent (2002-2006) PR, average weightsand maturity schedule

Use resulting estimates of Fmsy, alpha, beta and sigmain a long-term projection of SSB and Catch

2. Non-parametric Approach

Perform an SSB per Recruit analysis

Incorporate recent (2002-2006) PR, average weightsand maturity schedule

Use resulting the estimate of Fmsy proxy (F40% MSP) and the cumulative distribution function of age 1 recruits from the 1981 to 2004 year classes in a long-term projection of SSB and Catch

1. Parametric Results

From the fit of the Beverton-Holt Stock Recruit Function

Fmsy = 0.28Bmsy = 60,304 mtMSY = 15,691 mtAlpha = 10,982.3Beta = 7,879.1Sigma = 0.626Steepness = 0.867

SSBmsy = 78,413 mt

MSY = 18,886 mt

AGEPRO Projection – Parametric Approach Fmsy = 0.28

2. Non-parametric Results

F40% = 0.23

SSBmsy = 51,408 mt

MSY = 10,294 mt

Yield and SSB per Recruit Analysis

SSBmsy = 90,278 mt

MSY = 19,673 mt

AGEPRO Projection – Non parametric ApproachFmsy = F40% = 0.23

SSBmsy = 90,278 mt

MSY = 19,673 mt

AGEPRO Projection – Non parametric ApproachFmsy = F40% = 0.23

SSBmsy = 71,150 mt

MSY = 14,936 mt

AGEPRO Projection – Non parametric ApproachFmsy = F40% = 0.23

Summary

MSY-based Reference Points (NEFSC 2002)

MSY = 16,600 mtSSBMSY = 82, 830 mtFMSY = 0.23

Revised Reference Points (This meeting)Projections

BH Y&SSB/R Non Par ParMSY 15,691 10,294 14,936 19,673SSBmsy 60,304 51,408 71,150 78,413Fmsy 0.28 0.23