Ontogenetic feeding shifts in two thresher shark species in the Galapagos Marine Reserve Arnés-Urgellés, Camila Galván-Magaña, Felipe Elorriaga-Verplancken, Fernando R. Delgado Huertas, Antonio Páez-Rosas, Diego Feeding strategies Isotopic niche Ontogenetic changes Tropical Eastern Pacific Thresher sharks This work was supported by the USFQ Collaboration Grant and Galapagos Science Center Grant (POA 2019). The Galapagos Science Centre (GSC), the Centro Interdisciplinario de Ciencias Marinas (CICIMAR) and the Instituto Andaluz de Ciencias de la Tierra (IACT-Granada) provided the necessary facilities and guidance to complete the laboratory phase of this study. Camila Arnés-Urgellés received fellowship from the Consejo Nacional de Humanidades, Ciencias y Tecnologías (CONAHCYT), which made the successful completion of this work possible. Fernando R. Elorriaga-Verplancken and Felipe Galván-Magaña received fellowships from the Instituto Politécnico Nacional (COFAA and EDI). Background The morphology and hunting behavior of thresher sharks make them easily distinguishable. These species are distributed across the Tropical Pacific Ocean feeding on squid and small fish. However, ontogenetic changes in their feeding strategies and habitat use are still unknown in this region. Methods We examined the δ13C and δ15N signatures in vertebral collagen from populations of Alopias pelagicus and Alopias superciliosus inhabiting the Galapagos Marine Reserve, focusing on three maturity stages: neonate, juvenile and adult. The vertebrae samples were taken from the seizure of illegal fishing activities carried out by a foreign fleet within the Galapagos archipelago. A total of thirty-three vertebrae from A. pelagicus and twenty-one from A. superciliosus were analyzed. Results Both species displayed significant differences in their δ15N values (p < 0.001), but not in δ13C (p = 0.230), suggesting a similar habitat use, but different prey consumption. Throughout their ontogeny, A. pelagicus displayed isotopic differences (p < 0.001), where neonates showed lower δ13C values and higher δ15N values compared to juveniles, probably because they still reflect the isotopic signatures of their mothers even after the first year of life. This study highlights trophic differences between both species, accompanied by an ontogenetic variation in A. pelagicus, aspects that allow us to understand the role of these species within the dynamics of the Eastern Tropical Pacific ecosystem. 2025-04-01T09:50:48Z 2025-04-01T09:50:48Z 2024-12-16 journal article Arnés-Urgellés C, Galván-Magaña F, Elorriaga-Verplancken FR, Delgado-Huertas A, Páez-Rosas D. 2024. Ontogenetic feeding shifts in two thresher shark species in the Galapagos Marine Reserve. PeerJ 12:e18681. DOI 10.7717/peerj.18681 https://hdl.handle.net/10481/103366 10.7717/peerj.18681 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional PeerJ