Abstract
Marine mammals are vulnerable to entanglement in nets and lines. To quantify their interactions with fishing gear, pinnipeds and small cetaceans were exposed to novel objects and simulated fishing gear in a zoological environment at SeaWorld San Diego. The objects included a line, a frame covered with gillnetting, and a pinger. Exposures were delivered using a baseline-exposure protocol documenting naïve responses and using repeated trials to measure habituation or sensitization. Responses to objects paired with the pinger differed strikingly from others, stimulating behaviors consistent with aversion in all species. Among pinnipeds, harbor seals (Phoca vitulina) left the test pool or touched the pinger-associated object less often, although some eventually manipulated it extensively. California sea lions (Zalophus californianus) reacted initially with avoidance, defensive, and agonistic behaviors. However, they quickly returned to baseline activities and readily took fish from pingered nets. Northern elephant seals (Mirounga angustirostris) reacted the least. Among the cetaceans, bottlenose dolphins (Tursiops truncatus) and a Pacific whitesided dolphin (Lagenorhynchus obliquidens) did not manipulate the objects but made fast investigative or agonistic passes near them. Jaw claps and surface-active behaviors were most common during pinger trials. Commerson’s dolphins (Cephalorhynchus commersonii) responded particularly strongly. Counts of some defensive or agonistic behaviors differed dramatically in the presence vs absence of the pinger, including bows (70 vs 0), roostertailing (117 vs 0), and fluke slaps (76 vs 2). Across seven trials, avoidance time in a refuge pool rose to > 90%, indicating sensitization strongly. Counts of some defensive or agonistic behaviors differed dramatically in the presence vs absence of the pinger, including bows (70 vs 0), roostertailing (117 vs 0), and fluke slaps (76 vs 2). Across seven trials, avoidance time in a refuge pool rose to > 90%, indicating sensitization. However, pinnipeds startled through gillnetting and Commerson’s dolphins charged it deliberately in spite of the pinger. Based on these experiments, it is more likely that pingers reduce entanglement by arousing aversion than by warning marine mammals to avoid a hazard.