Agonistic attacks on divers and submersibles by gray reef sharks, Carcharhinus amblyrhynchos: antipredatory or competitive?
Pursuit by a small wet submersible was used to release exaggerated-swimming display and subsequent attack in order to determine proximate causative factors. A total of 57 trials were conducted which tested the effect of: 1) species of shark, 2) bait vs. no bait, 3) grouping type–lone vs. aggregated, and 4) location on the reef. Ten high-speed strikes on the vehicle were elicited, all by gray reef sharks, Carcharhinus amblyrhynchos. Neither attack nor full display could be elicited from silvertip sharks, C. albimarginatus; blackfin reef sharks, C. melanopterus; or reef whitetip sharks, Triaenodon obesus. Gray reef sharks attacked in both baited and unbaited situations, but apparently more readily in the latter. Lone individuals (unbaited) seemed more prone to display and attack than those in aggregations. Attack probability was positively related to degree of cornering by reef or bottom. An oriented pursuit (following shark's every move), even at quite low speeds, seemed of primary importance. Motivation for display and attack remains uncertain and may differ with circumstance, but the sharks most likely regard the pursuing submersible as a predator (antipredatory motivation), rather than as a competitor (defense of rank or territory), and certainly not as food (predatory motivation).
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Document Type: Research Article
Publication date: 1986-01-01
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