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Preparing to launch: biologging reveals the dynamics of white shark breaching behaviour

Semmens, Jayson M., Kock, Alison A., Watanabe, Yuuki Y., Shepard, Charles M., Berkenpas, Eric, Stehfest, Kilian M., Barnett, Adam, Payne, Nicholas L.
Marine biology 2019 v.166 no.7 pp. 95
Arctocephalus pusillus pusillus, Carcharodon carcharias, accelerometry, biomechanics, energy, foraging, islands, predators, prediction, seals, sharks, South Africa
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.