Estimability of natural mortality and other population parameters in a length-based model: Pandalus borealis in Kachemak Bay, Alaska

Because stock-assessment models have become more complex, the question of e stimability of population parameters is important. We conducted simulation- estimation experiments with a length-based model of the pink shrimp (Pandal us borealis Kroyer) population in Kachemak Bay, Alaska, to compare the robu stness of various modeling approaches to specifications of natural mortalit y (M), catchability (q), a survey gear selectivity parameter (L-50), and da ta imprecision. Our goal was to determine the estimability of various param eters, particularly M, q, and L-50. Simulation results suggest that interan nual variations in M and L-50 could be estimated, if the underlying values have a trend over time. However, parameter q should be fixed at a chosen va lue, even when it varies over time. Estimated M for the Kachemak Bay P. bor ealis population increased in the 1980s, perhaps owing to increased predati on mortality by groundfish.