The trophic role of a large marine predator, the tiger shark Galeocerdo cuvier

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Sampling the muscle tissue of a tiger shark for isotope analysis. Photo: OCEARCH/Rob Snow

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Dr. Luciana Ferreira
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CITATION

Ferreira LC, Thums M, Heithaus MR, Barnett A, Abrantes KG, Holmes BJ, Zamora LM, Frisch AJ, Pepperell JG, Burkholder D, Vaudo J, Nowicki R, Meeuwig J, Meekan MG. 2017. The trophic role of a large marine predator, the tiger shark Galeocerdo cuvier. Scientific Reports, 7: art7641.

HIGHLIGHTS

• Our analysis of stable isotopes shows that the functional role of tiger sharks in food-webs varied among different marine habitats where they were sampled along the tropical and temperate coasts of Australia.

• Tiger sharks in Shark Bay and on the Great Barrier Reef had long-term diets based in seagrass and reef-associated food webs. In these habitats they are focused on turtles and dugong as prey.

• In contrast, when sharks were sampled in more temperate habitats such the waters off New South Wales and southern Queensland, the composition of their tissues reflected a diet based on more pelagic food-webs.

• Tiger sharks occupied roles at the top of food webs at Shark Bay in WA, and on the Great Barrier Reef, but not at Ningaloo Reef or off the coast of NSW.

• This means the local environment and prey community, appear to be the most important determinants of the diet of tiger sharks.

ABSTRACT

Tiger sharks were sampled off the western (Ningaloo Reef, Shark Bay) and eastern (the Great Barrier Reef; GBR, Queensland and New South Wales; NSW) coastlines of Australia. Multiple tissues were collected from each shark to investigate the effects of location, size and sex of sharks on δ13C and δ15N stable isotopes among these locations. Isotopic composition of sharks sampled in reef and seagrass habitats (Shark Bay, GBR) reflected seagrass-based food-webs, whereas at Ningaloo Reef analysis revealed a dietary transition between pelagic and seagrass food-webs. In temperate habitats off southern Queensland and NSW coasts, shark diets relied on pelagic food-webs. Tiger sharks occupied roles at the top of food-webs at Shark Bay and on the GBR, but not at Ningaloo Reef or off the coast of NSW. Composition of δ13C in tissues was influenced by body size and sex of sharks, in addition to residency and diet stability. This variability in stable isotopic composition of tissues is likely to be a result of adaptive foraging strategies that allow these sharks to exploit multiple shelf and offshore habitats. The trophic role of tiger sharks is therefore both context- and habitat-dependent, consistent with a generalist, opportunistic diet at the population level.

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Mean and standard deviation stable isotopic composition of each tissue for each of the locations sampled (SB = Shark Bay, GBR = Great Barrier Reef, NSW = New South Wales, QSCP = Queensland Shark Control Program) for (A) slow tissues (muscle, dermis, fin) and (B) multiple tissues (muscle, dermis, fin, red blood cells, plasma), for sites where multiple tissues were collected. Figure: Ferreira et al 2017.

FUNDING & ACKNOWLEDGEMENTS

Funding for this work was provided by the Royal Zoological Society of New South Wales through the Paddy Pallin Science Grant, the University of Western Australia, the Australian Institute of Marine Science, and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil). The authors also acknowledge Chris Fischer and the crew of the MV OCEARCH for the aid with logistics and field work, the Australian Animal Tracking and Monitoring System (AATAMS) for providing receiver data, and the Queensland Shark Control Program and the New South Wales Gamefishing Association for providing samples.