Ontogenetic feeding ecology of the scalloped hammerhead shark Sphyrna lewini in the Colombian Eastern Tropical Pacific

Abstract

Changes in feeding habits during ontogeny show that organisms can present shifts in foraging behavior during their life cycle, which can alter local trophic dynamics. Therefore, describing diet across species ontogeny clarifies the ecological niche and ecosystem role of marine predators. In this study, diet tracers (stable isotope analysis) were analyzed in 16 scalloped hammerhead sharks Sphyrna lewini, using δ13C and δ15N values of collagen in vertebral cross-sections to reconstruct diet across their ontogeny. Our results suggest that S. lewini occupies a broad isotopic niche due to the consumption of prey belonging to different trophic levels (δ15N: 7.6-13.0‰) of the food chain in both coastal and oceanic zones (δ13C: -17.2 to -14.1‰) during their lifetime. Accordingly, ontogenetic changes in diet and habitat use were suggested by differences in δ13C and δ15N across age groups, indicating high consumption of coastal prey at 0-2 yr, oceanic prey at ~2-4 yr, a shift to high coastal prey at >4 yr, and a shift to high coastal prey, along with the consumption of prey from multiple trophic levels through feeding ontogeny (estimated trophic position: 2.9-6.5). This study showed migration from coastal to oceanic zones in juvenile S. lewini, and their return to coastal habitats as adults, potentially related to the use of coastal zones (i.e. mangroves) in the Eastern Tropical Pacific, both as important feeding areas for neonates and as feeding and breeding grounds for adults.