ESR 17:83-92 (2012)  -  DOI: https://doi.org/10.3354/esr00418

Isotopic niches of the blue shark Prionace glauca and the silky shark Carcharhinus falciformis in the southwestern Indian Ocean

N. Rabehagasoa1,*, A. Lorrain2, P. Bach1, M. Potier3, S. Jaquemet4,5, P. Richard6, F. Ménard

1Institut de Recherche pour le Développement (IRD), UMR 212 EME (IRD/IFREMER/UM2), BP 50172, 97492 Ste Clotilde Cedex, La Réunion, France
2IRD, UMR LEMAR 195 (UBO/CNRS/IRD), BP 70, 29280 Plouzané, France
3IRD, UMR 212 EME, Avenue Jean Monnet, BP 171, 34203 Sète Cedex, France
4Université de la Réunion, Laboratoire Ecomar, Avenue René Cassin, 97715 Saint-Denis Cedex, France
5IRD, UMR 212 EME, Botany Department, Rhodes University, 6140 Grahamstown, South Africa
6Littoral, Environnement et Sociétés, UMR 6250 CNRS-Université de La Rochelle, 17042 La Rochelle, France

ABSTRACT: In the Indian Ocean, the blue shark Prionace glauca and the silky shark Carcharhinus falciformis represent the 2 main shark bycatch species in pelagic longline and purse seine fisheries, respectively. With the increasing market demand for fins, catches may increase in the future, with potential effects on ecosystem trophic functioning through top-down cascading effects. Knowledge of the species’ trophic ecology is therefore crucial but is limited by the lack of data from the Indian Ocean. Stable isotope analysis was therefore performed on muscle tissues (δ15N and δ13C) of these 2 shark species from the western Indian Ocean. Our study showed that body length, season, and zone effects were relatively small for the 2 species. However, significant δ13C differences between the 2 species suggest niche partitioning, with silky sharks having a more inshore foraging habitat than blue sharks. Finally, lower muscle δ15N values were observed in juvenile silky sharks caught by purse seiners around fish aggregating devices (FADs) compared to juveniles caught by longliners. One hypothesis is that FADs could act as an ecological trap for juvenile silky sharks, leading to a position at lowest trophic level for these individuals. However, different foraging habitats could also explain the observed patterns between juveniles. Although preliminary, our results provide a basis for the implementation of species-specific protection and management strategies.


KEY WORDS: Stable isotopes · δ13C · δ15N · Trophic ecology · Niche partitioning · Foraging habitat · Sharks


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Cite this article as: Rabehagasoa N, Lorrain A, Bach P, Potier M, Jaquemet S, Richard P, Ménard F (2012) Isotopic niches of the blue shark Prionace glauca and the silky shark Carcharhinus falciformis in the southwestern Indian Ocean. Endang Species Res 17:83-92. https://doi.org/10.3354/esr00418

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