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The influence of variable marine survival on fishery management objectives for wild steelhead

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

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The influence of variable marine survival on fishery management objectives for wild steelhead

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  1. The influence of variable marine survival on fishery management objectives for wild steelhead Dan Rawding & Charlie Cochran

  2. 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)

  3. 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

  4. 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 ?

  5. 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)

  6. SRR Reference Points

  7. Fishery Management • Is there a relationship between spawners & recruits? • Would more data help? • What is wrong?

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

  9. 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

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

  11. 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)

  12. Wind River MSY objectives

  13. 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

  14. 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

  15. 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

  16. 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)

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