Table_1_Disentangling Natural and Anthropogenic Forms of Mortality and Serious Injury in a Poorly Studied Pelagic Dolphin.XLSX

Killer whale (Orcinus orca) populations specialize in both prey and prey acquisition tactics around the world and may be a primary evolutionary driver of the habits of small cetaceans. Entanglement in fishing gear is the most significant anthropogenic threat to the survival of cetaceans worldwide. Distinguishing between natural and human-caused sources of mortality and injury is a key task in marine mammal conservation and management. In British Columbia (BC), Canada, mammal-eating killer whales co-occur with Pacific white-sided dolphins (Lagenorhynchus obliquidens). Bycatch mortality rates are unknown here due to lack of systematic fisheries observer coverage. Drawing from more than three decades of first-hand observations of killer whale attacks on Pacific white-sided dolphins, we identify common themes with respect to predatory behavior of killer whales and anti-predatory responses of dolphins. With input from veterinary pathologists, we outline clues to distinguish killer whale rake marks from scars and wounds likely to be caused by fishery interactions. We examined photographs of 415 well-marked Pacific white-side dolphins for evidence of injuries and scars consistent with either killer whale attacks or fishery interactions. In this case study, healed scars from interactions with killer whale predators were ∼8× more common than scars from fishery interactions (3.9 vs. 0.5%), suggesting that predation is a much bigger threat to Pacific white-sided dolphins in the study area than anthropogenic impacts, or that dolphins are much less likely to survive a fishery interaction than a predation attempt. To advance our knowledge on poorly studied species, multiple lines of evidence will be needed.

虎鲸（Orcinus orca）全球种群均存在猎物专化性，并演化出特有的猎食策略，其或为小型鲸类行为习性演化的核心驱动因素之一。渔具缠缚是全球范围内鲸类生存面临的最主要人为威胁。区分鲸类死亡与损伤的自然成因与人为成因，是海洋哺乳动物保护与管理工作的核心任务之一。在加拿大不列颠哥伦比亚省（British Columbia, 简称BC），以哺乳动物为食的虎鲸与太平洋斑纹海豚（Lagenorhynchus obliquidens）同域分布。由于缺乏系统性的渔业观察员覆盖机制，该区域的兼捕死亡率数据目前仍属未知。本研究基于三十余年来针对虎鲸袭击太平洋斑纹海豚的一手观测资料，梳理出虎鲸捕食行为与海豚反捕食行为的共性特征。在兽医病理学家的协助下，我们明确了可用于区分虎鲸齿刮痕迹与渔业交互所致伤痕及创口的鉴别线索。我们对415只带有清晰体表痕迹的太平洋斑纹海豚的影像资料进行了检查，以寻找符合虎鲸袭击或渔业交互特征的损伤与伤痕证据。本案例研究显示，由与虎鲸捕食者交互所致的愈合伤痕出现频率约为渔业交互所致伤痕的8倍（3.9% vs. 0.5%），这表明在研究区域内，捕食对太平洋斑纹海豚的威胁远大于人为活动影响；或说明海豚在渔业交互中存活的概率远低于虎鲸捕食事件中的存活概率。若要加深对研究程度较低物种的认知，需整合多维度的证据来源。