Age, growth and mortality of redthroat emperor Lethrinus miniatus (Pisces: Lethrinidae) from the southern Great Barrier Reef, Queensland, Australia

Abstract

Fractional age estimates were derived from thin-sectioned otoliths of redthroat emperor (Lethrinus miniatus) from two locations in the southern Great Barrier Reef, Australia, and were validated using marginal increment analysis. Whole otoliths of fish up to about 6 yrs of age provided reliable age estimates, but in older fish whole otoliths underestimated age, probably as a result of allometry in otolith growth. Von Bertalanffy growth parameter estimates from the Capricorn-Bunker population (L∞ = 52.1; k = 0.23; to = –1.43) are considered representative of the species in this latitude of the Great Barrier Reef. Mean lengths of the early age-classes of fish from the Swain Reefs were overestimated because of fishery selectivity, leading to biases in the growth parameters k (0.19) and to (–2.74). The instantaneous rate of total mortality (Z), calculated from age-based catch curves, was significantly higher for the Capricorn-Bunker Group population (0.70) than for the Swain Reefs population (0.43), probably because of historical differences in exploitation levels between the two areas.