Comparative selectivity on length at maturity among Alaskan sockeye

salmon fisheries

Neala KendallTom Quinn

School of Aquatic and Fishery SciencesUniversity of Washington

Seattle, WA, USA

M. Bond

Need for evaluating harvest selection

Life history traits are changing over time (Darimont et al. 2009 PNAS)

Need for quantifying harvest selection

Life history traits are changing over time (Darimont et al. 2009 PNAS)

Importance of quantifying harvest selection (Carlson et al. 2007 Ecology Letters, Edeline et al. 2007 PNAS)

Need for quantifying harvest selection

Life history traits are changing over time (Darimont et al. 2009 PNAS)

Importance of quantifying harvest selection (Carlson et al. 2007 Ecology Letters, Edeline et al. 2007 PNAS)

Evaluating implications of selection (Olsen et al. 2004 Nature, Heino and GodØ 2002 Bulletin of Marine Science)

Difficult to quantify fishery selection

Hutchings, Nature 2005

Fish caught

Length

Fishery selectivity curve

?

Alaska salmon: good model to study fishery selection

Semelparous Anadromous Length and age at maturity

easy to measure Know population size and

structure Long-term gillnet fisheries Large, long term data set

J. Carter

Research questions

Does fishery selection vary by fish length and sex?

J. Carter

Research questions

Does fishery selection vary by fish length and sex?

Are fish length at age changes over time correlated with fishery selection?

J. Carter

Alaska sockeye salmon fisheries

Bristol Bay

Upper Cook Inlet

Alaska

Methods

Yearly historical fishery reconstruction

Characterize annual length distributions in catch, escapement (not caught), and total run

Estimate:

1) Length-specific vulnerability

2) Selection differentials

Length frequency histogram example

Females

Males

-

100,000

200,000

300,000

450 500 550 600 650

Length (mm)

Num

ber o

f fis

h

Total run

Catch

Escapement

-

100,000

200,000

300,000

400,000

400 450 500 550 600 650

Length (mm)

Nu

mb

er

of f

ish

Total runCatchEscapement

Vulnerability profiles by length

Females

Males

199000

.20

.40

.60

.81

400 450 500 550 600 650

Upper Cook Inlet males

Body length (mm)

Vu

lne

rab

ility

1994

Body length (mm)

Vu

lne

rab

ility

1999

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

2002

Body length (mm)

Vu

lne

rab

ility

2003 00

.20

.40

.60

.81

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

199000.2

0.40.6

0.81

400 450 500 550 600 650

Upper Cook Inlet males

Body length (mm)

Vulnerability

1994

Body length (mm)

Vulnerability

1999

400 450 500 550 600 650

Body length (mm)

Vulnerability

2002

Body length (mm)

Vulnerability

2003 00.2

0.40.6

0.81

400 450 500 550 600 650

Body length (mm)

Vulnerability

1990 1994 1999 2002 2003

400 650 400 650 400 6500

10

1

Selection on length: SSDs

SSD

Larger fish are escaping to

spawn than are getting caught

+-

Smaller fish are escaping to

spawn than are getting caught

Standardized selection differential =

lengthescapement – lengthtotal run

std. deviation of lengthtotal run

0

0.1

0.2

0.3

-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

Standardized selection differential

Pro

po

rtio

n f

req

ue

nc

y

Male

Female

J. Carter

Female SSDs more consistently negative than male SSDs

Female average

Male average

Fishery selection on Bristol Bay sockeye salmon and length at age changes over time

Differential fishery selection on ocean age 2 fish

Pro

po

rtio

n f

req

ue

nc

y

Pro

po

rtio

n f

req

ue

nc

y

Standardized selection differential

Standardized selection differential

Nushagak

0.0

0.1

0.2

0.3

0.4Male

Fem ale

Naknek-Kvichak

0.0

0.1

0.2

0.3

0.4

Egegik

0.0

0.1

0.2

0.3

0.4

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4

Ugashik

0.0

0.1

0.2

0.3

0.4

Togiak

0.0

0.1

0.2

0.3

0.4

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4

P < 0.001P = 0.143

0.0

0.1

0.2

0.3

0.4Male

Fem ale

0.0

0.1

0.2

0.3

0.4Male

Fem ale

0.0

0.1

0.2

0.3

0.4Male

Fem ale

0.0

0.1

0.2

0.3

0.4Male

Fem ale

P < 0.001P < 0.001

P < 0.001P = 0.002

P < 0.001

P = 0.051

P = 0.010P = 0.756

Nushagak

Naknek-Kvichak

Egegik

Ugashik

Togiak

Nushagak

Naknek-Kvichak

Ugashik

Togiak

1960 1970 1980 1990 2000 2010Year

NushagakMale

Female

Naknek-Kvichak

Egegik

1960 1970 1980 1990 2000 2010Year

Average length of ocean age 2 fish has decreased over time

Ave

rag

e le

ng

th (

mm

)

slope=-0.60

slope=-0.64

slope=-0.26

slope=-0.31

slope=-0.16

slope=-0.05slope=-0.19

slope=-0.21

slope=-0.16

slope=-0.21

450

550

450

550

Ave

rag

e le

ng

th (

mm

)

450

550

450

550

Egegik

Ugashik

Togiak

Nushagak

Naknek-Kvichak

slope: P = 0.003

slope: P = 0.033

slope: P = 0.005

slope: P = 0.218

slope: P = 0.869

SSDs somewhat correlated with decreasing length at age over time

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

-0.20 -0.15 -0.10 -0.05 0.00

Standardized selection differential

Slo

pe

of

oc

ea

n a

ge

2

len

gth

ov

er

tim

e

Conclusions

Are larger than average fish more vulnerable to being caught?

YESFish caught

ConclusionsConclusions

Males

Does the fishery harvest different lengths of males than females?

YES

Length

Females

Conclusions

Are fish length at age changes over time correlated with fishery selection?

YES Fishing districts that harvest

larger fish show a greater decline in fish length at age

over time

Conclusions

Mary Beth Loewen and Matt Foster, ADFG Mark Willette and Terri Tobias, ADFG Tim Baker, ADFG Jeff Hard, NOAA Fisheries Alaska Salmon Program, UW Funding:

School of Aquatic and Fishery Sciences Alaska Sustainable Salmon Fund National Science Foundation Gordon and Betty Moore Foundation

Acknowledgements

J. Bennis J. Carter

Bristol Bay—100% gillnets

Chignik—100% purse seines

Alitak—mixed purse seines/gillnets

Vulnerability differs by length & sex example

Females

J. Carter

Males

0

0.2

0.4

0.6

0.8

1

450 500 550 600 650

Length (mm)V

uln

era

bilit

y

0

0.2

0.4

0.6

0.8

1

430 480 530 580 630

Length (mm)

Vu

lne

rab

ilit

y

0

0.2

0.4

0.6

0.8

1

Vu

lne

rab

ility

Females

Vulnerability curves differ among years

J. Bennis

Length (mm)

1980 1991 2002

420 620420 620 420 620

J. Carter

Vulnerability profiles

1989

00

.20

.40

.60

.81

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

1990

Body length (mm)

Vu

lne

rab

ility

1991

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

1992

Body length (mm)

Vu

lne

rab

ility

1993

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

1994

Body length (mm)

Vu

lne

rab

ility

1995

Body length (mm)

Vu

lne

rab

ility

1996

Body length (mm)

Vu

lne

rab

ility

1997

Body length (mm)

Vu

lne

rab

ility

1998

00

.20

.40

.60

.81

Body length (mm)

Vu

lne

rab

ility

1999

00

.20

.40

.60

.81

Body length (mm)

Vu

lne

rab

ility

2000

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

2001

Body length (mm)

Vu

lne

rab

ility

2002

400 450 500 550 600 650

Body length (mm)

Vu

lne

rab

ility

2003

Body length (mm)

Vu

lne

rab

ility

Chignik female

Vulnerability profiles

Chignik male

1989

00

.20

.40

.60

.81

400 500 600

Body length (mm)

Vu

lne

rab

ility

1990

Body length (mm)

Vu

lne

rab

ility

1991

400 500 600

Body length (mm)

Vu

lne

rab

ility

1992

Body length (mm)

Vu

lne

rab

ility

1993

400 500 600

Body length (mm)

Vu

lne

rab

ility

1994

Body length (mm)

Vu

lne

rab

ility

1995

Body length (mm)

Vu

lne

rab

ility

1996

Body length (mm)

Vu

lne

rab

ility

1997

Body length (mm)

Vu

lne

rab

ility

1998

00

.20

.40

.60

.81

Body length (mm)

Vu

lne

rab

ility

1999

00

.20

.40

.60

.81

Body length (mm)

Vu

lne

rab

ility

2000

400 500 600

Body length (mm)

Vu

lne

rab

ility

2001

Body length (mm)

Vu

lne

rab

ility

2002

400 500 600

Body length (mm)

Vu

lne

rab

ility

2003

Body length (mm)

Vu

lne

rab

ility

Vulnerability profiles

Upper Cook Inlet female

198900

.20

.61

450 550 650

Body length (mm)

Vu

lne

rab

ility

1990

Body length (mm)

Vu

lne

rab

ility

1991

450 550 650

Body length (mm)

Vu

lne

rab

ility

1992

Body length (mm)

Vu

lne

rab

ility

1993

450 550 650

Body length (mm)

Vu

lne

rab

ility

1994

Body length (mm)

Vu

lne

rab

ility

1995

Body length (mm)

Vu

lne

rab

ility

1996

Body length (mm)

Vu

lne

rab

ility

1997

Body length (mm)

Vu

lne

rab

ility

1998 00

.20

.61

Body length (mm)

Vu

lne

rab

ility

199900

.20

.61

Body length (mm)

Vu

lne

rab

ility

2000

Body length (mm)

Vu

lne

rab

ility

2001

Body length (mm)

Vu

lne

rab

ility

2002

Body length (mm)

Vu

lne

rab

ility

2003

Body length (mm)

Vu

lne

rab

ility

2004

450 550 650

Body length (mm)

Vu

lne

rab

ility

2005

Body length (mm)

Vu

lne

rab

ility

2006

450 550 650

Body length (mm)

Vu

lne

rab

ility

2007

Body length (mm)

Vu

lne

rab

ility

Vulnerability profiles

Upper Cook Inlet male

198900

.20

.61

400 500 600 700

Body length (mm)

Vu

lne

rab

ility

1990

Body length (mm)

Vu

lne

rab

ility

1991

400 500 600 700

Body length (mm)

Vu

lne

rab

ility

1992

Body length (mm)

Vu

lne

rab

ility

1993

400 500 600 700

Body length (mm)

Vu

lne

rab

ility

1994

Body length (mm)

Vu

lne

rab

ility

1995

Body length (mm)

Vu

lne

rab

ility

1996

Body length (mm)

Vu

lne

rab

ility

1997

Body length (mm)

Vu

lne

rab

ility

1998 00

.20

.61

Body length (mm)

Vu

lne

rab

ility

199900

.20

.61

Body length (mm)

Vu

lne

rab

ility

2000

Body length (mm)

Vu

lne

rab

ility

2001

Body length (mm)

Vu

lne

rab

ility

2002

Body length (mm)

Vu

lne

rab

ility

2003

Body length (mm)

Vu

lne

rab

ility

2004

400 500 600 700

Body length (mm)

Vu

lne

rab

ility

2005

Body length (mm)

Vu

lne

rab

ility

2006

400 500 600 700

Body length (mm)

Vu

lne

rab

ility

2007

Body length (mm)

Vu

lne

rab

ility

Using estimated selectivities, model ideal

length and age at maturity under different

harvest scenarios (JØrgensen et al. 2009 Evol.

Apps.)

Calculate maturation reaction norms for

spawning populations

J. Bennis J. Carter

Future work, extensions

J. BennisJ. Bennis