Preparing to launch: biologging reveals the dynamics of white shark breaching behaviour
In comparison to other behaviours, large predators expend relatively large amounts of energy foraging for prey, based on expected high return. Documenting how they manage costs and benefits of feeding is difficult, particularly for marine predators. In July and August of 2004 and 2005, we combined animal-borne video, accelerometry and depth sensors to examine the underwater behaviour during white shark (Carcharodon carcharias) breaching at Seal Island, South Africa (34.1373°S, 18.5825°E)—where sharks launch from the water while attacking Cape fur seals (Arctocephalus pusillus pusillus). We show that breaching begins at depths up to 20 m, is characterised by a brief (~ 7 to 16 s) ascent to the surface during which pitch angle increases by ~ 30° and both tail-beat frequency and swim speed (determined using biomechanical principles) increase by a maximum of 6.5-fold (0.39–2.50 Hz and 1.0–6.5 m s−1, respectively). Sharks also demonstrated the ability to rapidly adjust their approach to the seal during ascent. Dominant tail-beat frequency during breaching was 2.1–4.2 times higher (0.83–1.67 Hz) than during non-predatory ascents (0.4 Hz), suggestive of the large increase in power required to breach. Examination of foraging behaviour through biologger deployments may play an increasingly important role in predicting the resource requirements of large predators and developing appropriate conservation measures, as their populations are generally under threat world-wide.
We thank G. Wilhelm (National Geographic) for clamp design, G. Marshall, K. Abernathy, P. Greene and M. Thorpe (National Geographic) for logistical support, L. Best for logging the footage and the South African Navy (Simonstown) for providing free harbour facilities for the research vessel. The following people are thanked for their help during fieldwork: K. Laroche, M. Hardenberg, A. de Vos, A. Casagrande, T. Lodge and numerous volunteers. We also thank Pete Klimley and an anonymous reviewer for improving this manuscript. This work was supported by a South African National Research Foundation Bursary (to A.A.K.); SEAChange Programme funding (to A.A.K.); Save Our Seas Foundation funding (to A.A.K.); Japan Society for Promotion of Science Invitational Fellowships for Research in Japan (S13196 & L15560 to J.M.S.) and a National Institute of Polar Research (Japan) Visiting Professorship (to J.M.S.).
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
Crittercam attachment and biologging methodology was approved by the South African Department of Environmental Affairs, Oceans and Coasts permitting authority and carried out in accordance with the approved guidelines described in permits V1/1/5/1 and V1/8/5/1.
Supplementary video 1. Animal-borne video of a white shark Carcharodon carcharias preparing to breach on a Cape fur seal Arctocephalus pusillus pusillus at Seal Island, South Africa. (MOV 13135 kb)
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