White Shark

The great white shark, Carcharodon carcharias, is the oceans most iconic predator. In the the realm of marine research, much is known about the white shark. We know white sharks can grow to at least 6 m in length and weigh up-to 3,000 kg [1]. We also know white sharks occur throughout temperate, subtropical and sometimes tropical waters with a cosmopolitan distribution. They are frequently encountered off South Africa [2], Southern Australia [3], New Zealand [4], northern California[5], Mexico [6] and North-Eastern United states [7]. The diet of white sharks mostly consists of finfish, rays and other sharks [8], although they also known to intermittently visit pinniped (seal/sea-lion) colonies for food [8, 3]. Their migrations aren’t neat or uniform, where some individual white sharks spend most of their lives in coastal water, some move regularly into open oceans [9] and patterns of movement appear different for males, females, and juveniles [10]. Some individuals also show a tendency to return to a previously occupied location (known as site fidelity) [11] and tagging and genetic studies have shown there is some sub-structuring of populations of white sharks world wide [11-15].

Occurrence of great white sharks

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[map from National Geographic Magazine].

However, since researching animals underwater is extremely difficult, there is also much that we don’t know about white sharks. There is no definitive agreement regarding exactly how long white sharks can live for and there is no recored sighting of great whites mating or giving birth. We also don’t really know at what age white sharks reach maturity and the estimates we do have are still debated in the scientific literature [see 16-18]. But most importantly for conservation and management, we have yet to determine how many white sharks there are living in our oceans globally, how connected their populations are, and how they might adapt to the changing oceans (climate change/ ocean acidification and warming)? An estimate of population size has been calculated for white sharks found in Australia by Hillary et al., (2018) [19]. The researchers used a fisheries-independant, DNA  based method called Close-Kin-Mark-Recapture (CKMR). The study estimated adult abundance in the year 2017 to be between 750 (however it could be anywhere between confidence intervals = 470-1,030) in the east of Australia and 1,460 (confidence intervals = 760-2,250) in the west of Australia. This has not been completed for other populations of white sharks in other parts of the world to date, and does not provide an indication as to how populations may have increased or decreased over time.

Thats where Project GenoJaws steps in. The project will investigate the effective population of global populations of white sharks in our oceans, their connectivity and adaptive potential. Effective population size (Ne) is the genetic vault that carries the gene pool of the population for future generations. Scientifically it is defined  the size of an “ideal” population of animals that would have the same rate of inbreeding or decrease in genetic diversity due to genetic drift, as the real population of interest. Providing estimates of Ne is important for understanding the adaptive potential of white sharks to environmental and anthropogenic pressures including climate change and fishing pressure. This investigation will also provide real data to government and policy makers so they can conduct a reasonable and rational debate about the future of white sharks in our oceans.

References

[1] Mollet, H.F., Cailliet, G.M., Klimley, A.P., Ebert, D.A., Testi, A.D. and Compagno, L.J.V., 1996. A review of length validation methods and protocols to measure large white sharks. Great White Sharks: the biology of, pp.91-108.

[2] Bonfil, R., Meÿer, M., Scholl, M.C., Johnson, R., O’brien, S., Oosthuizen, H., Swanson, S., Kotze, D. and Paterson, M., 2005. Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science, 310(5745), pp.100-103.

[3] Bruce, B.D., Stevens, J.D. and Malcolm, H., 2006. Movements and swimming behaviour of white sharks (Carcharodon carcharias) in Australian waters. Marine Biology, 150(2), pp.161-172.

[4] Duffy, C.A., Francis, M.P., Manning, M.J. and Bonfil, R., 2012. Regional population connectivity, oceanic habitat, and return migration revealed by satellite tagging of white sharks, Carcharodon carcharias, at New Zealand aggregation sites. Global perspectives on the biology and life history of the white shark, pp.301-318.

[5] Boustany, A.M., Davis, S.F., Pyle, P., Anderson, S.D., Le Boeuf, B.J. and Block, B.A., 2002. Satellite tagging: expanded niche for white sharks. Nature, 415(6867), pp.35-36.

[6] Santana-Morales, O., Sosa-Nishizaki, O., Escobedo-Olvera, M.A., Oñate-González, E.C., O’Sullivan, J.B. and Cartamil, D., 2012. Incidental catch and ecological observations of juvenile white sharks, Carcharodon carcharias, in western Baja California, Mexico: Conservation implications. Global perspectives on the biology and life history of the white shark, pp.187-198.

[7] Skomal, G.B., Chisholm, J. and Correia, S.J., 2012. Implications of increasing pinniped populations on the diet and abundance of white sharks off the coast of Massachusetts. Global Perspectives on the Biology and Life History of the White Shark’.(Ed. ML Domeier.) pp, pp.405-418.

[8] Malcolm, H., Bruce, B.D. and Stevens, J.D., 2001. A review of the biology and status of white sharks in Australian waters. Hobart: CSIRO Marine Research.

[9] Bruce, B.D., 2008. The biology and ecology of the white shark, Carcharodon carcharias. Sharks of the open ocean: Biology, fisheries and conservation, pp.69-81.

[10] Domeier, M.L. and Nasby-Lucas, N., 2007. Annual re-sightings of photographically identified white sharks (Carcharodon carcharias) at an eastern Pacific aggregation site (Guadalupe Island, Mexico). Marine Biology, 150(5), pp.977-984.

[11] Bruce, B.D., Stevens, J.D. and Bradford, R., 2005. Site fidelity, residence times and home range patterns of white sharks around pinniped colonies. CSIRO Marine Research.

[12] Blower, D.C., Pandolfi, J.M., Bruce, B.D., Gomez-Cabrera, M.D.C. and Ovenden, J.R., 2012. Population genetics of Australian white sharks reveals fine-scale spatial structure, transoceanic dispersal events and low effective population sizes. Marine Ecology Progress Series, 455, pp.229-244.

[13] Pardini, A.T., Jones, C.S., Noble, L.R., Kreiser, B., Malcolm, H., Bruce, B.D., Stevens, J.D., Cliff, G., Scholl, M.C., Francis, M. and Duffy, C.A., 2001. Sex-biased dispersal of great white sharks. Nature, 412(6843), p.139.

[14] Gubili, C., Duffy, C.A., Cliff, G., Wintner, S.P., Shivji, M., Chapman, D., Bruce, B.D., Martin, A.P., Sims, D.W., Jones, C.S. and Noble, L.R., 2012. Application of molecular genetics for conservation of the white shark, Carcharodon carcharias, L. 1758. Global Perspectives on the Biology and Life History of the White Shark, pp.357-380.

[15] Gubili, C., Duffy, C.A., Cliff, G., Wintner, S.P., Shivji, M., Chapman, D., Bruce, B.D., Martin, A.P., Sims, D.W., Jones, C.S. and Noble, L.R., 2012. Application of molecular genetics for conservation of the white shark, Carcharodon carcharias, L. 1758. Global Perspectives on the Biology and Life History of the White Shark, pp.357-380.

[16] Hamady, L.L., Natanson, L.J., Skomal, G.B. and Thorrold, S.R., 2014. Vertebral bomb radiocarbon suggests extreme longevity in white sharks. PloS one, 9(1), p.e84006.

[17] Tanaka, S., Kitamura, T., Mochizuki, T. and Kofuji, K., 2011. Age, growth and genetic status of the white shark (Carcharodon carcharias) from Kashima-nada, Japan. Marine and Freshwater Research, 62(6), pp.548-556.

[18] Braccini, M., Taylor, S., Bruce, B. and McAuley, R., 2017. Modelling the population trajectory of West Australian white sharks. Ecological Modelling, 360, pp.363-377.

[19] Hillary, R.M., Bravington, M.V., Patterson, T.A., Grewe, P., Bradford, R., Feutry, P., Gunasekera, R., Peddemors, V., Werry, J., Francis, M.P., et al. (2018). Genetic relatedness reveals total population size of white sharks in eastern Australia and New Zealand. Scientific Reports 8.