Tiger Shark

Tiger Sharks, Galeocerdo cuvier, are so named for the tiger-like stripes observed on juvenile individuals. They are the largest of the Carcharhiniformes and are found throughout the worlds oceans in tropical and warm-temperate waters. Tiger sharks are an ’opportunistic scavenger’. They are known to consume rays, turtles, teleost fish and sea snakes, and can alter their diet depending on context and habitat to include invertebrates and other organisms at lower trophic levels [1].

Tiger sharks are currently classified as ‘near threatened’ on the ICUN red list [2] and scientific evidence – a reduction in long term catch rates and a decrease in average size – suggests tiger shark populations are in decline [3]. Within their range tiger sharks are targeted by commercial, recreational, artisanal and shark control fishing operations, and they face other pressures both anthropogenic and environmental. Unfortunately, our ability to understand the extent the decline in tiger sharks and the impacts of fishing and other pressures is currently limited by our lack of understanding of tiger shark abundance, diversity and migration. Patterns in movements of tiger sharks show that while they do have a propensity to return to specific habitats and locations on a regular basis (known as site fidelity) they typically undergo large migrations within and between ocean basins. These observation have been confirmed with genetic information, and together they indicate that tiger shark populations are wide-ranging, crossing important jurisdictional, management and conservation boundaries [4,5]. This makes population-level management and conservation efforts difficult, and a deeper understating global population structure and connectivity of tiger sharks within and among global ocean basins is needed. Project GenoJaws is investigating tiger sharks using targeted genetic information from both contemporary and historical sources to highlight past and present demographic parameters which are critically important to the future of these sharks in our oceans.

References

[1] Ferreira, L.C., Thums, M., Heithaus, M.R., Barnett, A., Abrantes, K.G., Holmes, B.J., Zamora, L.M., Frisch, A.J., Pepperell, J.G., Burkholder, D. and Vaudo, J., 2017. The trophic role of a large marine predator, the tiger shark Galeocerdo cuvier. Scientific Reports, 7.

[2] Simpfendorfer, C. 2009. Galeocerdo cuvier. The IUCN Red List of Threatened Species 2009: e.T39378A10220026.

[3] Holmes, B.J., Sumpton, W.D., Mayer, D.G., Tibbetts, I.R., Neil, D.T. and Bennett, M.B., 2012. Declining trends in annual catch rates of the tiger shark (Galeocerdo cuvier) in Queensland, Australia. Fisheries Research, 129, pp.38-45.

[4] Bernard, A.M., Feldheim, K.A., Heithaus, M.R., Wintner, S.P., Wetherbee, B.M. and Shivji, M.S., 2016. Global population genetic dynamics of a highly migratory, apex predator shark. Molecular ecology, 25(21), pp.5312-5329.

[5] Holmes, B.J., Williams, S.M., Otway, N.M., Nielsen, E.E., Maher, S.L., Bennett, M.B. and Ovenden, J.R., 2017. Population structure and connectivity of tiger sharks (Galeocerdo cuvier) across the Indo-Pacific Ocean basin. Royal Society Open Science, 4(7), p.170309.