Stomach contents and stable isotope analysis reveal ontogenetic shifts and spatial variability in Brama australis diet

Many marine fisheries rely on production and energy flow in the pelagic zone; thus, sustainable management of exploited pelagic fishes benefits from insight into temporal, spatial, and ontogenetic variability in the trophic ecology of these species. Here, we analyze stomach contents and stable isotopes to reveal spatial variability (focusing on two fishing grounds, north and south of an oceanographic barrier in the Pacific Ocean) and ontogenetic changes (contrasting immature and mature) in Southern Ray’s Bream (Brama australis) diet composition in Chilean waters. Stomach contents analysis indicated that euphausiids were predominant components of the diet in both fishing grounds and ontogenetic stages. Patterns of prey long-term assimilation, revealed in Bayesian mixing models of predator and prey isotopic values of δ¹⁵N and δ¹³C, differed from diet as indicated in stomach contents. Shrimps and crustacean larvae were more important than euphausiids in the northern and southern fishing ground, respectively. In both fishing grounds, diet shifted after maturity towards increased use of shrimps. Combining methods of stomach contents analysis and stable isotopes analysis is a powerful approach to determining predator–prey relationships and energy flow in pelagic fishes.