Estimation of age-specific migration in an age-structured model

Estimation of age-specific migration in an age-structured model

S.E. Miller, T.J. Quinn II, and J.N. Ianelli

Estimation of age-specific migration in an age-structured modelThis is part of Resiliency of Gadid Stocks to Fishing and Climate Change
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Description

The standard Eastern Bering Sea (EBS) walleye pollock (Theragra chalcogramma) age-structured stock assessment model has no spatial dimension.
To better understand its dynamics on finer spatial and temporal
scales, an age-specific movement (ASM) model was developed. The ASM model stratifies the assessment data into two regions (northwest [NW] and southeast [SE] EBS), includes movement, and allows population parameters to be region-specific. The ASM model was used to evaluate hypotheses on age-specific movement between the NW and SE and covered years 1977 to 2005 and ages-3 to 10+. Estimates of biomass and population parameters from the ASM model were similar to those of the standard stock assessment model. The ASM model fitted the yearly observed catch numbers and yield, and catch-age composition data well, but some population parameters were highly uncertain or highly correlated. More in-depth information on finer spatial and temporal scales is needed from spatially explicit studies of EBS walleye pollock. Having additional information from a mark-recapture study would help to stabilize the ASM model and allow some assumptions to be relaxed.

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