Foraging depth depicts resource partitioning and contamination level in a pelagic shark assemblage: insights from mercury stable isotopes

Type Article
Date 2021-08
Language English
Author(s) Besnard Lucien1, Le Croizier Gaël1, 2, Galván-Magaña Felipe3, Point David2, Kraffe Edouard1, Ketchum James4, Martinez Rincon Raul Octavio5, Schaal Gauthier1
Affiliation(s) 1 : Laboratoire des Sciences de L'Environnement Marin (LEMAR), UMR 6539 CNRS/UBO/IRD/IFREMER, BP 70, 29280 Plouzané, France
2 : UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 Avenue Edouard Belin, 31400 Toulouse, France
3 : Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Av. IPN S/n, 23096 La Paz, B.C.S., México
4 : Pelagios-Kakunja, Cuauhtémoc 155, 23096 La Paz, B.C.S., México
5 : CONACyT-Centro de Investigaciónes Biológicas Del Noroeste, S.C. (CIBNOR), Av. IPN 195, 23096 La Paz, B.C.S., México
Source Environmental Pollution (0269-7491) (Elsevier BV), 2021-08 , Vol. 283 , P. 117066 (11p.)
DOI 10.1016/j.envpol.2021.117066
WOS© Times Cited 1
Keyword(s) Trophic ecology, Top predator, Mercury stable isotopes, Resource partitioning, Foraging depth, Mercury accumulation
Abstract

The decline of shark populations in the world ocean is affecting ecosystem structure and function in an unpredictable way and new ecological information is today needed to better understand shark roles in their habitats. In particular, the characterization of foraging patterns is crucial to understand and foresee the evolution of dynamics between sharks and their prey. Many shark species use the mesopelagic area as a major foraging ground but the degree to which different pelagic sharks rely on this habitat remains overlooked. In order to depict the vertical dimension of their trophic ecology, we used mercury stable isotopes in the muscle of three pelagic shark species (the blue shark Prionace glauca, the shortfin mako shark Isurus oxyrinchus and the smooth hammerhead shark Sphyrna zygaena) from the northeastern Pacific region. The Δ199Hg values, ranging from 1.40 to 2.13 ‰ in sharks, suggested a diet mostly based on mesopelagic prey in oceanic habitats. We additionally used carbon and nitrogen stable isotopes (δ13C, δ15N) alone or in combination with Δ199Hg values, to assess resource partitioning between the three shark species. Combining Δ199Hg resulted in a decrease in trophic overlap estimates compared to δ13C/δ15N alone, demonstrating that multi-isotope modeling is needed for accurate trophic description of the three species. Mainly, it reveals that they forage at different average depths and that resource partitioning is mostly expressed through the vertical dimension within pelagic shark assemblages. Concomitantly, muscle total mercury concentration (THg) differed between species and increased with feeding depth. Overall, this study highlights the key role of the mesopelagic zone for shark species foraging among important depth gradients and reports new ecological information on trophic competition using mercury isotopes. It also suggests that foraging depth may play a pivotal role in the differences between muscle THg from co-occurring high trophic level shark species.

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Besnard Lucien, Le Croizier Gaël, Galván-Magaña Felipe, Point David, Kraffe Edouard, Ketchum James, Martinez Rincon Raul Octavio, Schaal Gauthier (2021). Foraging depth depicts resource partitioning and contamination level in a pelagic shark assemblage: insights from mercury stable isotopes. Environmental Pollution, 283, 117066 (11p.). Publisher's official version : https://doi.org/10.1016/j.envpol.2021.117066 , Open Access version : https://archimer.ifremer.fr/doc/00688/80050/