Age, growth, mortality rates and corresponding yield estimates using otoliths of the tropical red snappers, Lutjanus erythropterus, L. malabaricus and L. sebae, from the central Great Barrier Reef

Abstract

Otoliths of L. erythropterus, L. malabaricus and L. sebae from the central Great Barrier Reef contain a well defined series of opaque and translucent increments known to be deposited annually. These three species are relatively long-lived, and grow slowly after becoming reproductively mature. Age estimates up to 32 years for L. erythropterus, 20 years for L. malabaricus and 22 years for L. sebae were much higher than those previously reported from other northern Australian waters. Age estimates obtained from counts of increments on whole otoliths were consistently much lower and more imprecise, at all ages compared with counts from sectioned otoliths. Precision of counts from whole otoliths declined significantly with increasing fish age. The regression of sectioned age on otolith weight revealed consistent linear relationships among all three species. To explore the fishery research and management implications of these biases, age estimates from the two ageing methods were used to construct comparative growth and mortality parameters and model yield-per-recruit values under contrasting harvest strategies. While the von Bertalanffy growth functions were not significantly different for the two methods, the underestimates of age from whole otoliths caused serious over-estimation of natural mortality. Serious overfishing could occur if these estimates were applied for fishery management purposes.