SCRS Assessments of Western Atlantic Bluefin Tuna Clay E. Porch Southeast Fisheries Science Center U.S. National Marine Fisheries Service.

SCRS Assessments of Western Atlantic Bluefin Tuna

Clay E. PorchSoutheast Fisheries Science Center

U.S. National Marine Fisheries Service

OUTLINE

•DATA

•METHODS

•ASSESSMENTS

•PROJECTIONS

•RESULTS OF 2006 ASSESSMENT

•KEY SOURCES OF UNCERTAINTY

DATA

Total catch (TASK I)Landings + dead discards

0

10000

20000

30000

40000

50000

60000

1950 1960 1970 1980 1990 2000

Ca

tch

es

(t)

MEDAT.WAT.E

DATA

Total catch (TASK I)

Catch at size (TASK II)Size frequencies of samples

(by nation, fleet, gear, time/area) raised to total catch

ATW LL

0

10

20

30

40

50

60

70

80

90

100

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Year

%

ATW oth

0

10

20

30

40

50

60

70

80

90

100

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Year

%

ATW PS

0

10

20

30

40

50

60

70

80

90

100

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Year

%

ATW LL

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

Fis

h in

CA

S

ATW oth

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

Fis

h in

CA

S

ATW PS

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

Fis

h in

CA

S

Quality of Size Data

LL

RR/HL

PS

•All commercial landings in Canada and US measured

• Japanese longline not well sampled for size

•Other fisheries adequate

•Some historical gaps (substitutions!)

1980

DATA


Catch at size (TASK II)

Indices of abundance (GLM)Larval surveyCanada TL (SWNS, GSL)

10+US RR (NE US, various sizes)

1-10+Japan LL (GOM, Area 2) 2-

10+US LL (GOM)

10+

Indices of abundance

No consistent changes inCPUE

U.S. East Coast RR

0

1

2

3

4

1990 1995 2000 2005 2010Year

Rel

ativ

e in

dex

SMSM

LGSM

LGMED-LG

U.S. GOM

0

1

2

3

4

1985 1990 1995 2000 2005 2010Year

Rel

ativ

e in

dex

ADULT GOM

Japan LL

0

1

2

3

4

1970 1975 1980 1985 1990 1995 2000 2005 2010Year

Rel

ativ

e in

dex

JLL West

CANADA

0

1

2

3

4

1975 1980 1985 1990 1995 2000 2005 2010Year

Rel

ativ

e in

dex

SW Nova Scotia

Gulf St. Lawrence

GOM: Larval

0

1

2

3

4

5

6

7

8

1975 1980 1985 1990 1995 2000 2005 2010Year

Rel

ativ

e in

dex

DATA


Catch at size (TASK II)

Indices of abundance (GLM)

TaggingConventional Electronic?

METHODS

Converting Catch at size (CAS) to Catch at age (CAA)

•Age data from reading hard parts rare, but size data are more plentiful

•Method of choice has been age slicing

(assigns range of lengths to specific age classes)

Age-slicing (program AGEIT)

1.Assumes growth curve knownconsistently assign too young or old

2.Assumes equal overlap in lengths of adjacent age classes

• smears year classes (smooths CAA)

• difficult to age older fish (plus groups)

3.AlternativesAge-length keys, Multifan

METHODS

Age-slicing (Convert CAS to CAA)

Standardizing CPUE (GLM)

Stock assessment algorithmBase model: ADAPT VPA Others examined:

ProductionASPMSCA

ADAPT SPECIFICATIONS

Terminal selectivities: F1 = 0.318F2, F3=F2, F5=F4, F7=F6, F9=F8

F-ratios (F10/F9):1970-73 1.0 1974-81 estimated1981- lognormal prior

(1.14,0.25)

Indices: lognormal, equal variance

Natural mortality: constant at 0.14

PROJECTION SPECIFICATIONS

Recruitment: constant at 1976-2001 mean

(2002-2004 recruitments deemed unreliable

and replaced by 1976-2001 mean)

Fishing: selection/avail. = 2001-03 mean

(last year, 2004, deemed unreliable)

Mixing: negligible

0

100000

200000

300000

400000

500000

600000

1960 1970 1980 1990 2000 2010

Rec

ruit

s

2002 SA

2006 Base

0

10000

20000

30000

40000

50000

60000

1970 1980 1990 2000 2010

SS

B

2002 SA

2006 Base

0

0.1

0.2

0.3

0.4

0.5

1970 1980 1990 2000 2010

Fis

hin

g m

ort

alit

y 8+

2002 SA

2006 Base

Consistent with 2002 SA Less optimistic estimates of 1994 and 1997 year classes

More optimistic view

of recent F’s

RESULTS OF 2006 ASSESSMENT

Projections

SSB/SSBMSY

0.0

0.5

1.0

1.5

2.0

2000 2005 2010 2015 2020 2025

Year

0 MT

500 MT

1,000 MT

1,500 MT

2,100 MT

2,300 MT

2,500 MT

2,700 MT

3,000 MT

Current (2006) Catch (including discards) 1,929 tShort-term Sustainable Yield ~2,300 tMaximum Sustainable Yield (MSY|R) 3,200 (3,000-3,400)Relative Spawning Stock Biomass B2004/B1975 0.18 B2004/BMSY|R 0.41 (0.29-0.54)Relative Fishing Mortality3

F2004/FMSY|R 1.7 F2004/F0.1 3.1 F2004/Fmax 1.7Management Measures: 2,100 t TAC from 2007 inc. dead disc [Rec. 06-06] 2,700 t TAC from 2003 inc. dead discards [Rec. 02-07] 30 kg (115 cm FL) min. size with 8% tol. [Rec. 98-07] No directed fisheries in Gulf of Mexico [Rec. 98-07]

F2004 is taken to be the geometric mean of the estimates for 2001-2003

BFTW summary table

State of stock: low U.S. catches

• Plausible explanations(1) that availability of fish to the United States fishery was low(2) the overall size of population in the west declined substantially

• Evidence (SCRS/2007/171)(1) Canada and Japan did not have abnormally low catches

CPUE series from Gulf of St. Lawrence at high levels since 2004 CPUE series from GOM do not show consistent decline

(2) some abundance indices suggest decline declining size composition in some areas small changes in F suggested by tag data despite declining catches

• Conclusion(1) No strong evidence to favor either explanation over the other(2) However, the failure of a fishery to take half of its TAC for several

years, and other new evidence reviewed by the committee, heightened concern that the estimate of stock status from the 2006 assessment may be optimistic

Management recommendations

• Commission responded positively, making Rec. 06-06, which establishes a quota of 2,100 MT

• However, the Committee is even more concerned about status of west stock than it was a year ago. Further advice provided after the next assessment (2008).

• Evidence accumulating that both productivity of west stock and west bluefin fisheries linked to the east stock. One plausible explanation for failure of west fishery totake TAC in recent years is that it is partly dependent on

east fish, and east fish now less available to the west • Therefore, management actions taken in the eastern

Atlantic and Mediterranean are likely to impact recovery in the west Atlantic (SCRS 2006 Agenda Item 15.6.)

BFT Statement of work

Data Submission:“It is essential, in particular,

that catch, catch-at-age and tagging data through 2006 be final a few months prior to the meeting to allow preparatory works andanalyses.

Data through 2006 end March 2008Data for 2007 1 week prior


Assessment:“In the case of the West stock,

mainline advice should be based on results from validated and documented software retained in the ICCAT catalog. These catalog entries need to be completed by April 2008”


Assessment:

1.Update 2006 assessment (VPA)2.VPA using new age-growth info.

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35

Age

Len

gth

(F

L, cm

)

Predicted (Turner and Restrepo)

SC Age

Predicted (Neilson and Campana)

West Atlantic Otolith Readings by S. Campana Shown in Comparison With theTurner and Restrepo (1994) Growth Curve


Assessment:

1.Update 2006 assessment (VPA)2.VPA using new age-growth info.3.VPA using new reproductive

info.

Age of BFT in LL landings from GOM


Assessment:


info.4.VPA with mixing

• Using conventional tag data• Using electronic tagging data• Using results from otolith

comp.


Assessment:


info.4.VPA with mixing

• Using conventional tag data• Using electronic tagging data• Using results from otolith

comp.5.Alternative models

Multi-area tag-recapture

•ONE STOCK (1971-1979) Trans-Atlantic

tag rec.

•TWO STOCKS (1980-present) 2 spawning grounds Distinct biol. char. Catch distribution Small interchange

•ONE STOCK (1971-1979) Trans-Atlantic

tag rec.

•TWO STOCKS (1980-present) 2 spawning grounds Distinct biol. char. Catch distribution Small interchange

ESTIMATION: CONVENTIONAL TAGS

Tew (%)

Tw

e (%

)DIFFUSION OVERLAP

NO MIXING DIFFUSION OVERLAP AIC=2870 AIC=893 AIC=897

T=(0.4, 7.6)% T=(0.0, 11.4)%

RESULTS WITH POP-UP TAGS

East

0

200

400

600

800

1000

1200

1970 1980 1990 2000

Ad

ult

s x

103

West

0

100

200

300

400

500

600

700

1970 1980 1990 2000

Ad

ult

s x

103

1) Improper accounting of fates

2) Limited coverage in time and space3)How to interpret fine-scale motions

on coarse model grid (e.g., two-area VPA)

4)Eastern contamination

PITFALLS OF USING TAGS

4) Eastern contamination

PITFALLS OF USING POP-UP TAGS

0

10000

20000

30000

40000

50000

60000

70000

1970 1974 1978 1982 1986 1990 1994 1998 2002 2006

Mediterranean

East Atlantic

Otolith microconstituent

analysis

L = nsy pasy log pasy

Assuming samples taken at

randon from catch

WHAT ELSE?

^

Projection assumptions

WHAT ELSE?

0.E+00

1.E+05

2.E+05

3.E+05

4.E+05

5.E+05

6.E+05

0 10000 20000 30000 40000 50000 60000

SSB

Re

cru

itm

en

t

Series1

Beverton & Holt vs. regime shift?

Photo acknowledgmentsBarbara BlockMolly LutcavageEric PrinceNOAA Photo Gallery

Photo acknowledgmentsBarbara BlockMolly LutcavageEric PrinceNOAA Photo Gallery

QUESTIONS?

SCRS Assessments of Western Atlantic Bluefin Tuna Clay E. Porch Southeast Fisheries Science Center U.S. National Marine Fisheries Service.

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