The Influence of Spatial Dynamics on Predation Mortality of Bering Sea Walleye Pollock

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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

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Eastern Bering Sea Yields and Biomass
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Eastern Bering Sea Food Web
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Consumption of Walleye Pollock
Walleye Pollock
Arrowtooth flounder
Pacific cod
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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.
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Model Processes Within Each Time Step
Migration
Age Update
Calculations across all areas
Consumption
Immigration
Calculations within each area
Harvest
Maturity
Spawning
Natural Mortality
Growth
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Model Dynamics
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Eastern Bering Sea Survey Areas
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Age Ranges of Stock Groups
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Data Sources
EBS Trawl survey - Annually, 1979-present Observer
Sampling Program - Annually, 1979-present Echo
Integration Trawls (EIT) - Triennially,
1982-present FOCI Trawls -- 1994,1995
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Data Sources for Each Model Component
Migration -- Trawl surveys, EIT
cruises Suitabilities -- MSVPA modeling Consumptio
n -- 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
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Maturity and Growth Functions
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Consumption
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
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Distribution by age
Age 1
Age 2
Age 3
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Effects of Migration on the Relative Amount of
Predation
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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