Variations in sex, length and age compositions of commercial catches of Platycephalus fuscus (Pisces : Platycephalidae) in New South Wales, Australia

Abstract

Commercial landings of dusky flathead (Platycephalus fuscus) from four estuaries in New South Wales (NSW), Australia, were sampled for data on sex, length and age composition between February and July each year for 2–3 years between 1995 and 1997. Landings primarily contained female fish, ranging from 55% to 93% by number for different estuaries. Flathead sampled in commercial catches ranged from 30 cm to 96 cm total length (TL), but the majority were 33–50 cm TL. Fish >40 cm TL were primarily female and male fish >45 cm TL were uncommon. The length composition of catches differed between gillnets of different mesh sizes, with the average length of fish being least in the smallest allowed mesh size of 70 mm. Fish were aged by otolith interpretation and the analysis of marginal increments indicated that one opaque and one translucent growth zone was formed each year; the opaque zone being deposited in June–August (winter) and first observed in September–October (spring). Commercial landings included fish aged 2–11+ years, but fish aged 2–4+ years dominated landings in all estuaries. The total mortality of dusky flathead in each estuary was estimated by catch curve analysis and was relatively high, ranging from 0.45 to 1.64. The data indicate that dusky flathead may be heavily exploited in NSW.