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

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

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

Elements of Ecosystem-Based Fisheries Management Models Accurate Predictive Data Sources Statistically Robust MODELMODEL Relevant Dynamics

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

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

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

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

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

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

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

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

1.Natural Mortality is estimable 2.Predation Mortality is estimable Preliminary Results Pacific Cod Arrowtooth Flounder Walleye Pollock

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