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Marine Ecology Progress Series

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MEPS 732:101-117 (2024)  -  DOI:

Resource partitioning in hammerhead shark species out-migrating from coastal ecosystems in the Gulf of California

Lucien Besnard1,*, Gaël Le Croizier1, Felipe Galván-Magaña2, Margaux Mathieu-Resuge1, Edouard Kraffe1, Raúl O. Martínez-Rincón3, Fabienne Le Grand1, Antoine Bideau1, Gauthier Schaal1

1Univ Brest, CNRS, IRD, Ifremer, LEMAR, 29280 Plouzané, France
2Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, 23096 La Paz, BCS, Mexico
3CONACyT-Centro de Investigaciones Biológicas del Noroeste, S.C. (CIBNOR), Av. IPN 195, 23096 La Paz, BCS, Mexico
*Corresponding author:

ABSTRACT: Juveniles of large hammerhead shark species occupy coastal nurseries before migrating offshore to reproduce. In the central Gulf of California, artisanal elasmobranch fisheries have reported catches of juvenile scalloped Sphyrna lewini and smooth S. zygaena hammerhead sharks, but their local foraging habits are yet to be fully understood. In this study, the trophic niches of both hammerhead species as well as of sympatric Pacific sharpnose sharks Rhizoprionodon longurio were investigated using stable isotope values (δ13C, δ34S and δ15N) and fatty acid compositions in whole blood and muscle tissues. Despite interspecific similarities among trophic niches, smooth hammerheads were characterized by lower δ13C, higher δ34S and greater proportion of docosahexaenoic acid (DHA) in both tissues, suggesting they were already partly relying on offshore pelagic resources. For scalloped hammerheads, muscle reflected coastal dietary resources, while offshore trophic markers were detected in blood integrating prey signal over shorter time periods, indicating their more recent initiation of ontogenetic migration. Multidimensional niche calculation revealed low overlap between hammerhead shark trophic niches, implying that potential fine-scale differences in habitat use could reduce competition between these morphologically and ecologically similar species. In the meantime, the isotopic niches of juvenile scalloped and smooth hammerheads were smaller than that of Pacific sharpnose sharks, suggesting they could be more specialized consumers. Overall, the identification of foraging grounds for juvenile hammerhead sharks calls for a future characterization of their residency time in coastal ecosystems to further understand their interactions with fishing pressure in the Gulf of California.

KEY WORDS: Sphyrna spp. · Trophic niche · Carbon isotopes · Nitrogen isotopes · Sulfur isotopes · Fatty acids · Sympatric sharks · Ontogenetic habitat shift · Artisanal fisheries

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Cite this article as: Besnard L, Le Croizier G, Galván-Magaña F, Mathieu-Resuge M and others (2024) Resource partitioning in hammerhead shark species out-migrating from coastal ecosystems in the Gulf of California. Mar Ecol Prog Ser 732:101-117.

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