Kray F. Van Kirk, SFOS, UAF, Juneau Terrance J. Quinn II, SFOS, UAF, Juneau

1. A Multispecies Age-Structured Assessment for the Gulf of Alaska Kray F. Van Kirk, SFOS, UAF, Juneau Terrance J. Quinn II, SFOS, UAF, Juneau Jeremy S. Collie, GSO, URI, Narragansett ftkv@uaf.edu

2. U.S. Commissions on Ocean Policy last year recommended a move towards ecosystem-based fisheries management. Why? Collapse of multiple fisheries worldwide + Increased understanding of ecosystem complexities and species interconnectivity

3. Single-species models are a foundation What’s going on down there?

4. Elements of Ecosystem-BasedFisheries Management Models Relevant Dynamics Predictive Accurate MODEL Data Sources Statistically Robust

5. Virtual Population Analysis Relevant Dynamics • Begins with “terminal cohort” Abundance at oldest age = Catch at oldest age • Mortality (Z) = Catch • Backward calculation of abundance • Assumes catch measured without error • Underestimates abundance Statistically Robust Accurate Data Sources Predictive

6. Cohort Analysis Relevant Dynamics • Begins with “terminal cohort” • Backward calculation of abundance • Mortality (Z) = Fishery Mortality + Fixed Natural Mortality • Assumes catch measured without error Statistically Robust Accurate Data Sources Predictive

7. Statistical Age-Structured Analysis Relevant Dynamics • Begins with Recruitment • Forward calculation of abundance • Mortality (Z) = Fishery Mortality + Fixed Natural Mortality • Assumes catch measured with error Statistically Robust Accurate Data Sources Predictive

8. Multispecies Models (MSVPA) Relevant Dynamics • Forward from recruitment or backwards from terminal cohort • Involve two or more species connected by predation • Fixed Predation Mortality (from gut studies) • Assumes catch measured without error Statistically Robust Accurate Data Sources Predictive

9. Mass Balance Models (Ecosim) Relevant Dynamics • Balances consumption and production • Involve ALL species connected by predation • Z =Fishery Mortality + Fixed Predation Mortality + Fixed Natural Mortality • Assumes catch measured without error • Tunes assimilation parameters Statistically Robust ?? Accurate ?? Data Sources Predictive

10. Our Approach:Multispecies Age-Structured Assessment • Three species with close predator-prey links (Walleye Pollock, Pacific Cod, Arrowtooth Flounder) • Progress forward from recruitment • Flexible predation mortality • Based on gut studies • Incorporates both species and age of prey preferred by a given predator • Is responsive to predator and prey abundances • Catch is assumed measured WITH error • Gear selectivities are estimated by model

11. Age-Specific Fishing Mortality Residual Natural Mortality Age-Specific Predation Mortality YEAR ONE Production from Spawning Biomass YEAR TWO

12. Catch-at-Age Gut Studies Spawner-Recruit Data Data Reproduction Fishing Mortality (F) Predation Mortality (P) Residual Natural Mortality (RNM) Dynamics Catch measured with error Flexible Predation Mortality Reproduction estimated to meet dual demands of mortality and spawning biomass Statistics Forward progression allows predictive capacity Predictive Preliminary results produce RSS scores of less than 500 Accuracy

13. Preliminary Results • Natural Mortality is estimable • Predation Mortality is estimable Pacific Cod Arrowtooth Flounder Walleye Pollock

14. Next Step Assess the implications of model results for practical fisheries management.