Growth rate, age determination, natural mortality and production potential of the scarlet seaperch, Lutjanus malabaricus Schneider 1801, off the Pilbara coast of north-western Australia

Abstract

The age of scarlet seaperch, Lutjanus malabaricus, from deep waters (>100 m depth) on the continental shelf of north-western Australia was estimated by examining transverse sections of their sagittal otoliths. Ages were assigned based on counts of alternating opaque and translucent zones (annuli). The consistency of the readings showed that the otolith increments can be used for age determination. Otolith weight was strongly correlated with fish age providing confirmation that the opaque and translucent zones used to estimate age in this study are formed on an annual basis. Growth was found to be moderately slow. The maximum observed age for a male was 31 years corresponding to 802 mm FL. There was significant differential growth between the sexes in observed length-at-age, with males growing larger than females. The von Bertalanffy growth parameters were: L ∞=686.4 mm FL , K=0.180 yr −1, t 0=−0.33 for males, and L ∞=565.8 mm FL , K=0.262 yr −1, t 0=−0.09 for females. The annual instantaneous rate of natural mortality ( M) was estimated to be 0.112. The life history characteristics of L. malabaricus indicate that this species has a low-production potential and hence is vulnerable to overfishing. Harvest strategies should, therefore, be conservative and fishery managers need to consider harvest refugia in those fisheries where size at first capture cannot be manipulated by modifications to fishing gear, such as the demersal fish trawl and fish trap fisheries of Western Australia.