Stock Identification Of Leopard Coral Grouper (Plectropomus leopardus) And Orange-Spotted Grouper (Epinephelus coioides) In Saleh Bay: Implications For Capture Fisheries Management

Abstract

The delineation of grouper stocks in Saleh Bay is crucial for ensuring accurate and sustainable fisheries management. Currently, Saleh Bay exhibits high species diversity, with 21 grouper species identified. However, over the past five years, increased fishing activity has led to overexploitation, necessitating conservation measures. Grouper fishing takes place both inside and outside Saleh Bay, with the catches being landed in Sumbawa Island. While data on fishing activities inside Saleh Bay are well documented, information regarding fishing outside the bay, such as in Sailus Island and Medang Island, remains limited. Therefore, comprehensive catch recording is essential for future fisheries management. Additionally, it is important to determine whether the grouper stocks caught inside and outside Saleh Bay belong to the same population or are distinct. If they are separate populations, differentiated management strategies must be implemented to ensure the sustainability of grouper resources in the region. The objectives of this study have been addressed to assess characteristics and general condition of grouper fisheries in Saleh Bay, West Nusa Tenggara, Indonesia (chapter 3 and chapter 4), to delineate the stock of leopard coral grouper (P. leopardus) using various methods (morphology, fish parasite, and molecular genetics) between Saleh Bay and Sailus Island (chapter 5), to identify the stock of the orange-spotted grouper (E. coioides) using DNA barcoding in Saleh Bay, West Nusa Tenggara, Indonesia (chapter 6), and to identify stock of orange-spotted grouper (E. coioides) using fish parasites in Saleh Bay, West Nusa Tenggara, Indonesia (chapter 7). This study integrates multiple approaches to better understand the population dynamics of grouper fisheries in Saleh Bay. Stock identification is conducted through morphological analyses (morphometric-meristic), molecular genetics, and fish parasites. Additionally, fisheries conditions in Saleh Bay are examined using statistical modelling, including diversity indices, fish biological parameters, exploitation levels, and factors affecting Catch Per Unit Effort (CPUE) using Generalized Linear Models (GLMs). The findings of this research are expected to provide valuable insights into the status of grouper stocks and the environmental conditions in Saleh Bay. This information can serve as the foundation for developing sustainable fisheries management strategies for the future. By integrating morphometric, molecular genetics, and parasitological evidence, this study demonstrates consistent stock differentiation between Saleh Bay and adjacent comparison waters. For Plectropomus leopardus, morphometric discrimination indicates pronounced separation between specimens from Saleh Bay and Sailus Island, accompanied by different growth patterns both of localities. These findings are substantiated by genetic analyses, which reveal subpopulation level segregation between the two localities. Parasitological patterns further support this differentiation: endoparasite assemblages differ markedly in both composition and abundance, and these differences correspond with variation in stomach contents, implying spatial heterogeneity in prey resources and trophic dynamics. In Epinephelus coioides, evidence for localized population structure is indicated by DNA barcoding, which places Saleh Bay individuals within a distinct geographic cluster. This signal is consistent with parasitological results showing that parasite communities in Saleh Bay form a discrete assemblage relative to those observed in other waters. Therefore, based on three approaches provides support for recognizing Saleh Bay populations of P. leopardus and E. coioides as distinct stock units. Consequently, management interventions in Saleh Bay may be most effective when implemented under a spatially explicit framework that treats the Saleh Bay as an independent management unit to improve sustainable grouper fisheries management. Future research should prioritize broader spatiotemporal sampling, high resolution population genomics, otolith-based tracers, and refined parasite indicators to validate stock boundaries and mechanisms of differentiation. Integrating movement ecology, reproductive dynamics, and trophic studies will clarify demographic connectivity and local residency. Finally, implementing stock structure into management strategy evaluation supported by socioeconomic assessments will enable Saleh Bay to be managed as an effective, spatially explicit unit for long-term grouper fisheries sustainability.