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

Simulation-estimation experiments with a length-based mode for estimating estimability of population parameters in stock-assessment models showed good results in terms of confidence and reproducibility.

Abstract

Because stock-assessment models have become more complex, the question of estimability of population parameters is important. We conducted simulation-estimation experiments with a length-based model of the pink shrimp (Pandalus borealis Krøyer) population in Kachemak Bay, Alaska, to compare the robustness of various modeling approaches to specifications of natural mortality (M), catchability (q), a survey gear selectivity parameter (L 50 ), and data imprecision. Our goal was to determine the estimability of various parameters, particularly M, q, and L 50 . Simulation results suggest that interannual 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 value, even when it varies over time. Estimated M for the Kachemak Bay P. borealis population increased in the 1980s, perhaps owing to increased predation mortality by groundfish.