Non-lethal aging of tropical catch-and-release sport fishery species

Abstract

Non-lethal methods for deriving age estimates from species of conservation significance or those supporting catch-and-release sport fisheries can assist in their sustainable management. In this study we tested if dorsal spines provide equivalent age estimates to otoliths for two species of large tropical snappers (Lutjanus goldiei and L. fuscescens, Lutjanidae) that support a catch-and-release sport fishery in remote parts of Papua New Guinea. Comparison of putative age estimates from sections taken at the base, mid and tip of the dorsal spine revealed that the base sections provided the most similar ages to otoliths, while mid and tip sections underestimated otolith age, especially for older individuals. Dorsal spine base-sections provided equivalent age estimates to otoliths for both species across the full range of ages examined (up to 17 for L. goldiei, and 14 for L. fuscescens). Like other lutjanids, these species show a wide range in length-at-age. This means that small fish are not necessarily young fish, and recruitment could potentially fail for more than a decade before anglers or guides notice a lack of smaller fish in their captures, by which time the opportunity to identify and reverse the cause of recruitment failure may have passed. Dorsal spines provide an effective and minimally-harmful means of monitoring population age structure to ensure ongoing recruitment to the fishery, and offer the opportunity for engagement of anglers, guides, and community members in the sustainable management of this fishery.