Prey capture by the Pacific angel shark, Squatina californica: Visually mediated strikes and ambush-site characteristics

Pacific angel sharks ambush demersal fishes by rapidly lunging from the sea floor. These sharks consistently attacked rubber and plastic prey models d uring in situ experiments. Videotaped strikes ranged from approximately 30- 100 msec in duration and included extreme cranial elevations (as much as 90 degrees) toward the models. Eleven of 23 sharks tested attacked a fish mod el from beneath a transparent partition, which was designed to block near-f ield mechanical cues. Head-on approaches by the model elicited a big-her fr equency of attacks and shorter attack latencies than caudal approaches (fre quency, P = 0.04; latency, P = 0.03). Night attacks may have been facilitat ed by turbulence-generated bioluminescence. Resting sharks and vacated depr essions were usually adjacent to reefs, either facing or aligned parallel t o margins of nearby reefs, and oriented toward upslope directions. Four sha rks 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 visu ally is the most important cue for eliciting daytime attacks, (2) the shark s probably possess an anterodorsally directed field of vision, and (3) ambu sh sites are selected based on substrata characteristics likely to be assoc iated with prey availability.