The Influence of Spatial Dynamics on Predation Mortality of Bering Sea Walleye Pollock Pat Livingston, Paul Spencer, Troy Buckley, Angie Greig, and Doug Smith Alaska Fisheries Science Center Seattle WA

Eastern Bering Sea Yields and Biomass

Eastern Bering Sea Food Web

Arrowtooth flounder Walleye Pollock Pacific cod Consumption of Walleye Pollock

Recruitment Hypotheses 1) The drift of larval pollock spreads evenly across the Bering Sea shelf and the average distribution of adults (and their cannibalism) is sufficient to explain the observed pattern of population abundance. 2) The interannual variability in larval drift locations is the main force separating larvae from cannibalistic adults and is sufficient to explain the observed patterns of population abundance.

Migration Spawning Natural Mortality Age Update Consumption Harvest Growth Immigration Maturity Model Processes Within Each Time Step Calculations across all areas Calculations within each area

Model Dynamics

Eastern Bering Sea Survey Areas

Age Ranges of Stock Groups

Data Sources EBS Trawl survey - Annually, 1979-present Observer Sampling Program - Annually, 1979-present Echo Integration Trawls (EIT) - Triennially, 1982-present FOCI Trawls ,1995

Data Sources for Each Model Component Migration -- Trawl surveys, EIT cruises Suitabilities -- MSVPA modeling Consumption -- Model parameters tuned to bioenergetic modeling results Catch -- Observer sampling Growth -- Trawl surveys, observer sampling, FOCI cruises, EIT cruises Spawning -- Trawl surveys Maturity -- Trawl surveys Initial population sizes -- MSVPA modeling, OSCURS circulation model Mean lengths at age -- Trawl surveys, simulation modeling

Maturity and Growth Functions

Where S(l,L) pred,prey = suitability N(l) prey = Prey #’s by size group (l) and species W(l) prey = Prey weights by size group (l) and species N(L) pred = Predator #’s by size group (L) and species C(L) pred = Consumption by predator size group and species Consumption

Age 1 Age 2 Age 3 Distribution by age

Effects of Migration on the Relative Amount of Predation

Conclusions 1) Substantial data needs for a model with this level of detail 2) Model verification is complicated by the number of processes 3) Information on fishery and ecosystem interactions by spatial location is commonly requested of fishery scientists