Reproduction, sexually dimorphic growth, exceptional longevity and low natural mortality of the knifejaw, Oplegnathus woodwardi, from temperate waters in the south-eastern Indian Ocean

Abstract

This is the first study of the life history characteristics of the monotypic Oplegnathus woodwardi. A total of 371 samples were collected from waters along the continental shelf (depths 30–120 m) off south-western Australia from 2010 to 2014, with a further 31 individuals collected in 1978/1979. Maximum ages of 51 and 53 years obtained from these contemporary and historical samples, respectively, are markedly higher than previous age estimates of two congeners from South African waters, whose ages were based on counts of growth zones in whole otoliths. Traditional von Bertalanffy growth (vBG) curves provided the best fit to the length at age data for females and males of O. woodwardi, when compared to vBG curves with t0 constrained to − 0.5 or the four parameter Schnute growth curve. In south-western Australia O. woodwardi exhibits a spring-summer spawning period, which is consistent with other temperate demersal teleosts along this coast. The age-based life history characteristics of O. woodwardi determined from this study, provide important information from which to infer the inherent vulnerability of this species. This study also contributes toward the broader sustainable management of this species, particularly where life history information is unknown but higher catches and smaller length compositions likely render that fisheries resource to be at a higher risk.