Sardenne, F., Diaha, N. 'G. C., Amande, M. J., Zudaire, I., Couturier, L. I. E., Metral, L., et al. (2019). Seasonal habitat and length influence on the trophic niche of co-occurring tropical tunas in the eastern Atlantic Ocean. Can. J. Fish. Aquat. Sci., 76(1), 69–80.
Résumé: In the Gulf of Guinea, bigeye tuna (Thunnus obesus; BET) and yellowfin tuna (Thunnus albacares; YFT) are an important part of commercial fisheries and play a prominent ecological role as top predators. Using fatty acid profiles and carbon and nitrogen stable isotopes, we examined their trophic niche partitioning in this understudied region. Trophic niche overlap was high (> 70%), similar to percentages in other ocean basins. BET occupied a higher trophic position than YFT and fed on deeper prey (high delta N-15 values and high proportions of monounsaturated fatty acids). The trophic position of YFT decreased slightly in the last 15 years (delta N-15 values decreased by similar to 0.5 parts per thousand), suggesting a change in epipelagic communities, as observed in the eastern Pacific Ocean. Ontogenic changes were limited to BET. For both species, the dietary proportion of the diatom marker 20:5(n-3) increased in the seasonal upwelling area, highlighting the influence of seasonal habitat on the diet of tuna. The relatively lipid-rich muscle (similar to 6% dry mass) of Atlantic tropical tuna suggests a richer diet in this region than that of Indian Ocean tropical tuna and (or) differences in energy allocation strategies.
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Trystram, C., Rogers, K. M., Soria, M., & Jaquemet, S. (2017). Feeding patterns of two sympatric shark predators in coastal ecosystems of an oceanic island. Can. J. Fish. Aquat. Sci., 74(2), 216–227.
Résumé: Stomach contents and stable carbon and nitrogen isotope analyses (delta C-13 and delta N-15) 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 delta C-13 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 delta C-13 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.
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