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Prey Capture by the Pacific Angel Shark, Squatina californica: Visually Mediated Strikes and Ambush-Site Characteristics
William R. Fouts and Donald R. Nelson
Vol. 1999, No. 2 (May 7, 1999), pp. 304-312
Stable URL: http://www.jstor.org/stable/1447476
Page Count: 9
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Pacific angel sharks ambush demersal fishes by rapidly lunging from the sea floor. These sharks consistently attacked rubber and plastic prey models during in situ experiments. Videotaped strikes ranged from approximately 30-100 msec in duration and included extreme cranial elevations (as much as 90°) toward the models. Eleven of 23 sharks tested attacked a fish model from beneath a transparent partition, which was designed to block near-field mechanical cues. Head-on approaches by the model elicited a higher frequency of attacks and shorter attack latencies than caudal approaches (frequency, P = 0.04; latency, P = 0.03). Night attacks may have been facilitated by turbulence-generated bioluminescence. Resting sharks and vacated depressions were usually adjacent to reefs, either facing or aligned parallel to margins of nearby reefs, and oriented toward upslope directions. Four sharks that were identified based on natural pigment patterns returned to the near proximities (< 3 m) of previously occupied ambush sites. Based on our experiments and observations, we suggest that (1) prey movement sensed visually is the most important cue for eliciting daytime attacks, (2) the sharks probably possess an anterodorsally directed field of vision, and (3) ambush sites are selected based on substrata characteristics likely to be associated with prey availability.