Estimation of Von Bertalanffy Growth Parameters in the Presence of Size-Selective Mortality: A Simulated Example with Red Grouper

Abstract

Fish lengths back-calculated to all scale or otolith annuli are often used for estimating parameters of the von Bertalanffy growth equation in an attempt to increase sample size and presumably improve the fitted model. Lengths at early ages back-calculated from younger age-groups sometimes are greater than lengths at the same age estimated from older age-groups, referred to as Leeˈs phenomenon. Leeˈs phenomenon can be simulated with use of size-selective mortality and moving averages to incorporate error dependency in lengths at age, To evaluate the appropriateness of using back-calculated lengths at formation of all annuli in growth analyses when size-selective mortality is present, we used simulated data based on von Bertalanffy growth parameters and total mortality for red grouper Epinephelus morio from the southeastern U.S. Atlantic coast. Asymptotic length (L∞) and the growth coefficient (K) showed greater bias when estimated with back-calculated lengths at all annuli than when estimated only with back-calculated lengths at the most recent annuli whenever Leeˈs phenomenon (or its reverse) was present. One should use only lengths back-calculated to the most recent annuli when estimating growth parameters representative of a population.