UW Aquatic & Fishery Sciences Quantitative Seminar

Ian Taylor

UW School of Aquatic and Fishery Sciences, NMFS NWFSC

Hiding or dead? A comparison of the effects of dome-shaped selectivity and differential removal of fast-growing fish

Ian Taylor and Richard Methot


Two processes may skew length composition data toward smaller fish: larger fish unavailable to the fishing gear, and differential removal of the faster growing members of each cohort. Accurate estimation of population productivity will depend on whether the largest fish are hiding or dead, but these processes are confounded in the data. Furthermore, the use of dome-shaped selectivity functions is common in age-structured stock assessment models, while the modeling of length-based mortality within each cohort is not. The Stock Synthesis model is used as both simulation and estimation model to estimate the interacting effects of these two processes, and the potential error resulting from incorrect assumptions in stock assessment. The presentation will also include a follow-up on Rick Methot's April 24 discussion of refinements to the correction for bias in recruitment parameters.

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