Bottom-up and top-down controls of walleye pollock in the Eastern Bering Sea

Transcription

1 Bottom-up and top-down controls of walleye pollock in the Eastern Bering Sea Franz J. Mueter Sigma Plus, Fairbanks, Alaska, USA Brenda L. Norcross Michael C. Palmer IMS, SFOS, University of Alaska

2 Bottom-up control Recruitment limited by primary production (environmental variability) Ice extent / timing of retreat Cold pool extent Surface currents( larval transport) Wind mixing / Stratification

3 Ice extent / timing of retreat Stock-recruit residual R 2 = 0.11 (p = 0.064) R 2 = 0.28 (p = 0.002) R 2 = 0.16 (p = 0.023) Sea ice extent Week of ice retreat

4 Fate of primary production Early ice retreat Late bloom Warm SST High pelagic prod. Late ice retreat Early (ice-edge) bloom Cold SST High benthic prod. Stock-recruit residual (standardized) pollock yellowfin sole walleye pollock yellowfin sole

5 Yellowfin sole and walleye pollock Yellowfin sole stock-recruit residual r = (p < 0.001) Walleye pollock stock-recruit residual

6 Cold Pool extent 1992 Alaska > 2 0 C < 2 0 C Aleutians

7 Cold Pool extent Index of association modified and updated from Wespestad et al. (2000) Stock-recruit residual Index of association Smoothing spline with 95 R 2 = % confidence bands (p = 0.16) Cold Pool Index Cold Pool Index

8 Surface transport Center of Spawning From: Wespestad et al. (2000). ICES J. Mar. Sci 57:

9 Surface transport Stock-recruit residual R 2 = 0.11 (p = 0.046) Final latitude of larval drift (OSCURS trajectories)

10 Summer stratification R 2 = 0.38, p =0.002 Partial SR residual Onset of stratification (Julian day) (from Carol Ladd, PMEL, pers. comm.) May-Sep wind stress (m 3 /s 3 ) (St. Paul Island) Summer conditions best explained past variability in survival rates of walleye pollock

11 Best overall model: Retrospective analysis log(r t /S t ) = b 0 + b 1 * SSB t-2 + b 2 * Strat t-1 + b 3 * (Wind t-1 ) 2 + b 4 * Lat t-2 + ε τ log(recruits / SSB) Out-of-sample predictions Year class

12 Summary: Bottom-up controls Ice extent / timing of ice retreat Fate of primary production Oscillating Control Hypothesis Cold pool extent Cold pool hypothesis Surface transport Larval transport hypothesis Summer stratification / wind mixing New hypothesis??

13 Match / mismatch hypothesis Match Mismatch Stock-recruit residual Onset of stratification (Julian day) Stratification index from Carol Ladd (pers. comm.) Aboveaverage survival Belowaverage survival

14 Top-down control Recruitment limited by predation from top-predators Predation Cannibalism

15 Top-down control: Consumption of walleye pollock Total consumption of walleye pollock as high as 3.5 million t (Livingston & Lang 1996) Model estimates based on diet composition ~40% of juvenile production (age 0-1) consumed by adult pollock (age 2+) ~5% of the diet of age 2+ pollock consists of age 0-1 pollock (Kerim Aydin, pers. comm.)

16 Cannibalism: Stock-recruit relationship Strong density-dependence in spawnerrecruit relationship Age-2 log(recruits Recruits (billions) / SSB) Spawning Stock Biomass (1000 t)

17 Predation mortality Predation mortality accounts for 33% of remaining variability in log-survival ( ) Or as much as 76% of total variability in logsurvival Stock-recruit residual log(recruits / SSB) R 2 = 33% (p = 0.004) R 2 = 76% (p < 0.001) Age-1 predation mortality Age-1 predation mortality Predation estimates from Jurado-Molina and Livingston (pers. comm.)

18 Top-down control Predation mortality depends on Abundance of predators Primarily adult pollock Availability of juveniles to predators Spatial overlap: horizontal / vertical Age-1 mortality Index of association

19 Top-down control Index of spatial association as predictor of log-survival and recruitment observed predicted Stock-recruit residual R 2 = Index of association log(recruitment) Year class

20 Bottom-up and top-down controls Other predators Environmental control? Predation (age-0) (age-1) Prey availability Timing of summer bloom Wind mixing Fate of primary production Ice retreat

21 Special thanks to: Carol Ladd, PMEL Nick Bond, PMEL Dave Kachel, PMEL Jim Ianelli, AFSC Pat Livingston, AFSC