Nonlethal stable isotope analysis reveals consistent trophic growth of juvenile Atlantic goliath grouper Epinephelus itajara in Brazilian estuaries

Atlantic goliath grouper Epinephelus itajara (Lichtenstein, 1822) are classified as vulnerable by the IUCN and have decreasing local populations throughout their distribution due to overfishing and habitat degradation. Due to their protected status, basic life history information that can inform management and conservation is lacking for some local populations, including in Brazil. In the present study, we examined how delta 15N of juvenile Atlantic goliath grouper fin rays, a nonlethal method, varied with total length across two estuaries in Brazil. A total of 100 juvenile Atlantic goliath grouper (total length range: 95-505 mm) were analyzed, and we observed positive relationships between delta 15N and fish lengths (i.e., evidence of trophic growth). Among-estuarine slopes did not differ, suggesting trophic growth was consistent among sites despite different delta 15N values between the northernmost site and a group of southern sites, possibly reflecting different isotopic baselines. This study is the first effort to provide useful insights into the trophic ecology of juvenile Atlantic goliath grouper in Brazil, which could help address knowledge gaps and conserve this endangered species. The nonlethal methodology employed in this study could be used to advance our understanding of the trophic ecology of other vulnerable and endangered marine fishes and help inform conservation and management practices.