UW Aquatic & Fishery Sciences Quantitative Seminar

André Punt

UW School of Aquatic and Fishery Sciences

Estimating size transition matrices for hard-to-age species

Abstract

Three classes of method that have been used to estimate the size-transition matrices on which assessments of hard-to-age species, such as prawns and rock lobsters, are compared using Monte Carlo simulations based on the tiger prawn Penaeus semisculcatus. The results of these simulations suggest that not all methods perform equally well, and that some methods are extremely poor. The "best" methods, as identified in the simulations, are those which allow for individual variability in the parameters of the von Bertalanffy growth equation as well as the length (or age) at release. Assuming that rather than k varies among individuals tends to be more robust to violations of model assumptions. Four of the methods that perform "best" in the simulations are applied to data for two tiger prawn species and an endeavour prawn species in Australia's Northern Prawn Fishery to highlight the considerable sensitivity of model outputs to the method for analysing tag-recapture data.