Age, growth, mortality and population characteristics of the pearl perch, Glaucosoma buergeri Richardson 1845, from deeper continental shelf waters off the Pilbara coast of north-western Australia

Abstract

Pearl perch, Glaucosoma buergeri Richardson 1845, from deeper waters (> 100 m depth) on the continental shelf of north-western Australia were aged by examining transverse sections of their sagittal otoliths. Ages were assigned based on counts of alternating opaque and translucent zones (annuli). Otolith length and breadth (width) increased linearly with fish length, whereas otolith weight increased linearly with fish age. The continuous growth of the otoliths provides some evidence that the opaque and translucent zones used to estimate age in this study are formed on a regular basis. Parameters of the length–weight relationship were estimated, along with parameters of the von Bertalanffy growth function. The generalised von Bertalanffy growth function (total length-at-age, both sexes combined) for G. buergeri was Lt=512.7 (1 – e–0.139(t + 0.89)). There was no significant differential growth between the sexes in observed length-at-age. The oldest individual found was a male G. buergeri estimated to be 26 years of age. The annual instantaneous rate of natural mortality (M) was estimated to be 0.14. The slow growth, long life and low natural mortality rate indicate that G. buergeri is vulnerable to overfishing and that harvest strategies for this species should be conservative, given its low production potential.