Combining information on otolith morphometrics and larval connectivity models to infer stock structure of Plectropomus leopardus in the Philippines

Abstract

The leopard coral grouper Plectropomus leopardus is a high-value fish species in the live reef fish for food trade (LRFFT), with stocks declining continually due to increasing market demands and unsustainable fishing practices. Managing this resource is difficult due to lack of biological information on local stocks. This paper utilized phenotypic- and model-based methods to discriminate stocks of P. leopardus in 3 LRFFT hubs in the Philippines (Taytay, Quezon, and Tawi-Tawi). Phenotypic variation among sites was assessed using shape descriptors and landmark data of otoliths, while patterns of connectivity were inferred from a dispersal model of coral grouper larvae. Inferences suggest (1) the presence of distinct phenotypic stocks and (2) limited larval connectivity among sites. There was an inconsistency with how otolith shape discriminated stocks. While shape descriptors identified Tawi-Tawi as a separate unit, landmark data differentiated Quezon from the other sites. This suggests that different processes may influence otolith shape, thereby presenting a caveat when using otolith morphometrics in stock discrimination. Meanwhile, the dispersal model showed that Quezon and Tawi-Tawi distribute larvae primarily to the West Philippine Sea and Celebes Sea, respectively. Although the model showed that Taytay supplies larvae to both Quezon and Tawi-Tawi, these connections were weak. Model inferences showing all sites as important larval sources to different reefs, coupled with the presence of distinct phenotypic stocks based on otolith shape, suggest that each LRFFT hub is an independent management unit. Thus, identifying key drivers of stock decline is crucial in developing site-specific fishery management approaches.