Integrated Fatty Acid and Stable Isotope Niches Reveal Trophic Connections Among Sympatric Large-Bodied Sharks

Abstract

This study used a novel approach combining stable isotope data and condensed multivariate fatty acid data to define comparative niche space and overlap of six sympatric sharks from the south-west Indian Ocean: Galeocerdo cuvier, Sphyrna zygaena, Sphyrna lewini, Carcharias taurus, Carcharodon carcharias and Carcharhinus obscurus. G. cuvier had the smallest fatty acid niche space but exhibited the largest range in δ¹³C, suggestive of foraging across multiple environments (habitat generalist) but on nutritionally similar prey in a narrow trophic band (nutritional specialist). The remaining five species had comparatively higher δ¹⁵N, pelagic-based fatty acids and larger fatty acid niche spaces, suggesting they are nutritional generalists with a preference for higher trophic level prey. Niche space was not associated with conservation status despite declining populations for half of the species studied. This suggests that resource availability is not a limiting factor for these species and that their mobile nature provides them access to diverse habitats and resources, while exposing them to a broad range of anthropogenic threats, muting the relationship between conservation status and resource use. The combined approach allowed for a comprehensive representation of niche space, distinguishing species based on trophic level, basal carbon sources and pelagic and coastal prey consumption. The presented integrated approach provides greater detail and resolution of elasmobranch trophic ecology that could not be achieved with either fatty acid or stable isotope analysis alone.