Feeding patterns of two sympatric shark predators in coastal ecosystems of an oceanic island

Stomach contents and stable carbon and nitrogen isotope analyses (δ[sup.13]C and δ[sup.15]N) were used to investigate the trophic ecology of two apex predators, tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), from Reunion Island to describe their dietary habits at both the population and individual levels. In this oceanic island, the tiger and bull sharks were more piscivorous and teutophagous than noted in previous research from other localities. The δ[sup.13]C values suggested that bull sharks depended on more neritic organic matter sources than tiger sharks, confirming a coastal habitat preference for bull sharks. Moreover, the total length of the bull shark influenced δ[sup.13]C values, with smaller individuals being more coastal than larger individuals. All indicators suggest that there is a higher degree of similarity between individual tiger sharks compared with the more heterogeneous bull shark population, which is composed of individuals who specialize on different prey. These results suggest that the two species have different functions in these coastal habitats, and thus, they must be considered independently in terms of conservation and management. Les contenus stomacaux et des isotopes stables (δ[sup.13]C et δ[sup.15]N) ont ete utilises afin d'etudier l'ecologie trophique du requin tigre (Galeocerdo cuvier) et du requin bouledogue (Carcharhinus leucas) a l'ile de La Reunion dans le but de decrire leurs habitudes alimentaires aux echelles populationnelle et individuelle. Dans cette etude, les requins tigre et bouledogue sont plus piscivore et plus teutophages que precedemment indique dans d'autres endroits. Le δ[sup.13]C suggere que les requins bouledogue dependent de sources de matiere organique plus cotieres que les requins tigre, confirmant l'aspect cotier de leur habitat. De plus, le δ[sup.13]C est influence par la taille des requins bouledogue avec les plus petits individus plus cotiers. Tous les indicateurs suggerent une plus grande similitude entre les individus de requin tigre comparativement a la population de requins bouledogues composee d'individus heterogene, chacun etant specialise sur differentes proies. Ces resultats montrent que les deux especes etudiees ont des fonctions differentes dans les habitats cotiers, montrant l'importance de les considerer independamment l'une de l'autre en terme de conservation et de gestion.
Introduction Understanding the role of large predators in marine ecosystems is important, given that many of these populations are in steep decline, and therefore the critical ecological functions they provide [...]