The influence of variable marine survival on fishery management

objectives for wild steelhead

Dan Rawding & Charlie Cochran

Population Monitoring Program• Adult and smolt population estimated using

mark-recapture or mark-resight• Trout Creek adult census or trap count 1993-05

except 1995,96,& 97 -timing & redd surveys• Precision of mark-recapture population

estimates (95%CI) > + 20%• Wild Spawner equivalents

– Reproductive success of hatchery steelhead to the smolt stage ~ 30% (Kostow 2003)

– Reproductive success of hatchery steelhead to the adult stage ~ 12% (Leider et al. 1990 & Hulett et al. 1996)

Wind River SteelheadBiological Information

• ~95% summer and ~5% winter steelhead• Segregation of race is due to Shipherd Falls

– 4 falls/cascades from 2 to 4 meters• Summer steelhead sex ratio ~2:1 (F:M)• Repeat spawner rate ~ 6%• Repeats both spawners & recruits• Spawner-Recruit modeling assumes steelhead

are semelparous– therefore Smolt to Adult Survival (SAS) includes

repeats

Out of Subbasin Information

• Unaccounted for loss between BON and Shipherd Falls is ~17% and assumed to be harvest from Zone 6 and sport fishing

• Mortality not accounted for– BON Adults 1.4% & Smolts 13.4%– Caspian Terns (Rice & Sand Islands)~10%– Cormorants ~2%– Marine Mammals Predation (2%)– Mainstem fishing below BON (2%?)– Northern Pikeminnow predation ?

Terms

• Spawner-Recuit (SR) or Spawner-Recuit-Relationship (SRR)

• SRR– Assume lognormal errors– Beverton-Holt (BH)– Ricker (R) – Hockeystick (HS)– Quadratic & Logistical Hockeystick(QHS,LHS)

SRR Reference PointsBeverton Holt

0

400

800

1200

1600

2000

0 400 800 1200 1600 2000

Spawners

Rec

ruits

BH

Rplc

1/2 K

Hockeystick

0

400

800

1200

1600

2000

0 400 800 1200 1600 2000

Spawners

Rec

ruits

HS

Rplc

S* or MSY

Ricker

0

400

800

1200

1600

2000

0 400 800 1200 1600 2000

Spawners

Rec

ruits

R

Rplc

MSP

Logistical Hockeystick

0

400

800

1200

1600

2000

0 400 800 1200 1600 2000

Spawners

Rec

ruits

LHS

Rplc

NEQ KProd

Wind River Steelhead, Spawn Years 1993-2002

0

200

400

600

800

1000

0 200 400 600 800 1000

Spawners

Rec

ruits

Obs

Wind River Steelhead, Spawn Years 1993-2002

0

200

400

600

800

1000

0 200 400 600 800 1000

Spawners

Recr

uits

Obs

BH

R

HS

QHS

LHS

Fishery Management

• Is there a relationship between spawners & recruits?

• Would more data help?• What is wrong?

Parameter BH R HS QHS LHSIntrinsic Productivity NA 5.0 2.4 3.3 30.7Capacity/ Inflection 480 339 200 145 NA

Wind River Steelhead

0%

2%

4%

6%

8%

10%

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Smolt Outmigration Year

Smol

t to

Adu

lt Su

rviv

al• No, No, It’s the ocean• Smolt to adult survival ranged from 1% to 10%, or by a factor of 10

Wind River Steelhead, Spawn Year 1993-2004

0

10000

20000

30000

40000

50000

0 500 1000 1500

Wild Equivalent Spawners

Smol

ts

ObsBHRHSQHSLHS

Trout Creek, Spawn Year 1992-2003

0

1000

2000

3000

4000

5000

0 20 40 60 80 100

Wild Equivalent Spawners

Smol

ts

ObsRHSQHSLHSBH

Wind River Steelhead, Spawn Year 1993-2002

0

400

800

1200

1600

0 400 800 1200 1600

Wild Equivalent Spawners (R=f(S) * avg MS)

Rec

ruits

ObsBHRHSQHSLHSRplc

Wind River Steelhead, Spawn Year 1993-2002

0

400

800

1200

1600

0 400 800 1200 1600

Wild Equivalent Spawners (R=f(S) * low MS)

Rec

ruits

ObsBHRHSQHSLHSRplc

Wind River Steelhead, Spawn Year 1993-2002

0

400

800

1200

1600

2000

2400

0 400 800 1200 1600

Wild Equivalent Spawners (R=f(S) * high MS)

Rec

ruits

ObsBHRHSQHSLHSRplc

Wind River Steelhead, Spawn Years 1993-2002

0

400

800

1200

1600

0 400 800 1200 1600

Spawners

Recr

uits

Obs

BH

R

HS

QHS

LHS

Possible Solutions

• Annual recruitment adjustment based on marine survival index (climate, hatchery steelhead survival, wild steelhead survival)

• Covariate (climate, hatchery or wild steelhead survival) into SRR – Two Stage SRR

R = aS/(1+ aS/B) * MS- Hatchery smolt survival

R = aS/(1+ aS/B) * (HS)c

Possible Solutions (continued)• PDO or other ocean/climate index• PDO adjusted for smolt outmigration year

Wind River Steelhead

0%

2%

4%

6%

8%

10%

-1.5-1.0-0.50.00.51.01.5

PDO

Smol

t to

Adu

lt su

rviv

al

Fishery Management Objectives• Maximize Harvest?

– Maximum Sustainable Yield (MSY)– MSY as lower bound

• Maximize fishing opportunity (C&R)?• Maximize/maintain Freshwater Production?

– S* = minimum escapement to maximize smolt yield– ½ K = freshwater production @ 50% of capacity

• Maintain Genetic Diversity?– 500 spawners– WSP - 3000/ average age @ maturity (600 spawners)

Wind River MSY objectives

SAS prod Inflection S-msy prod cap S-msy prod Inflection S-msy1% 0.59 0.70 0.52% 1.19 1406 117 1.39 1013 131 1.03% 1.78 1406 372 2.09 1520 324 1.5 533 5334% 2.37 1406 534 2.78 2026 487 1.9 533 5335% 2.96 1406 648 3.48 2533 630 2.4 533 5336% 3.56 1406 734 4.18 3039 759 2.9 533 5337% 4.15 1406 801 4.87 3546 879 3.4 533 5338% 4.74 1406 856 5.57 4052 990 3.9 533 5339% 5.33 1406 901 6.26 4559 1094 4.4 533 533

10% 5.93 1406 940 6.96 5065 1192 4.8 533 533

Ricker Beverton-Holt Hockeystick

Summary

• MSY goals for low (3%)ocean survival 324 - 533• MSY goals for hi (6%) ocean survival 533 - 759• MSY goals for avg(4.5%)ocean survival 533-595• MSY goals are highly variable depending on

SAS - 117 (1%) to 1192(10%)• Precautionary approach suggest MSY as lower

bound• MSY goals for small steelhead populations may

compromise genetic diversity

Summary

• Current Wind River escapement goal 1,000 to 1,300 based on habitat model with good marine survival

• MSY goals for 4.5% SAS 533 - 595• Minimum genetic goal 500 - 600 spawners• SRR goals freshwater productivity (517 –

729)– Beverton-Holt Hockeystick

• ½ K = 729 S* = 532, S* for QHS = 517

Fishery Management• Wind River Steelhead are listed under ESA• Currently, WDFW manages steelhead

commercial & recreational fishery impacts in the Wind River and other Lower Columbia River populations for less than 10%

• Fishery management and escapement objectives for Wind River will be a compromise of science and policy

• Recovery planners advocate “extra spawners” (above MSY) to take advantage of habitat restoration or lessen extinction risk

Fishery Management• When fisheries are managed for fixed

escapement goals, they are more likely to meet escapement objectives

• When fisheries are managed for fixed harvest rates, they are more likely to meet fishing objectives

• If we desire more precise management, a fishery management with multiple thresholds or controls between 300 and 800 adults could be developed for this population (BC approach with conservation and target reference points)