Wright Bryan E, Riemer Susan D, Brown Robin F, Ougzin Aicha M, Bucklin Katherine A
Marine Mammal Research Program, Oregon Department of Fish and Wildlife, Corvallis, Oregon 97330, USA.
Ecol Appl. 2007 Mar;17(2):338-51. doi: 10.1890/05-1941.
The populations of many native species have increased or expanded in distribution in recent decades, sometimes with negative consequences to sympatric native species that are rarer or less adaptable to anthropogenic changes to the environment. An example of this phenomenon from the Pacific Northwest is predation by locally abundant pinnipeds (seals and sea lions) on threatened, endangered, or otherwise depleted salmonid (Oncorhynchus spp.) populations. We used survey sampling methodology, acoustic telemetry, and molecular genetics to quantify the amount of harbor seal (Phoca vitulina) predation on a depressed run of coho salmon (O. kisutch) and to determine whether some seals consumed a disproportionately higher number of salmonids than others. Based on a probability sample totaling 759.5 h of observation, we estimated that seals consumed 1161 adult salmonids (95% CI = 503-1818 salmonids) during daylight hours over an 18.9-km estuarine study area in Oregon during an 84-d period in fall 2002. Simultaneous tracking of 56 seals via an acoustic telemetry array indicated that a small proportion of marked seals (12.5%) exhibited behavior that was consistent with specialization on salmonids. These seals spent the majority of their time in the riverine portion of the study area and did so disproportionately more at night than day. Genetic analysis of 116 salmonid structures recovered from 11 seal fecal samples suggested that coho salmon accounted for approximately one-half of total salmonid consumption. Though subject to considerable uncertainty, the combined results lead us to infer that seals consumed 21% (range = 3-63%) of the estimated prespawning population of coho salmon. We speculate that the majority of the predation occurred upriver, at night, and was done by a relatively small proportion of the local seal population. Understanding the extent and nature of pinniped predation can provide important inputs into risk assessments and other modeling efforts designed to aid the conservation and recovery of salmonids in the Pacific Northwest. Such understanding may also help inform management actions designed to reduce the impact of pinniped predation on salmonids, which potentially range from short-term lethal removal programs to long-term ecosystem restoration and protection efforts.
近几十年来，许多本地物种的数量有所增加或分布范围有所扩大，有时会对同域分布的本地物种产生负面影响，这些物种更为稀有或对人为环境变化的适应能力较差。太平洋西北地区这种现象的一个例子是，当地数量众多的鳍足类动物（海豹和海狮）捕食受到威胁、濒危或数量已减少的鲑科鱼类（大麻哈鱼属）种群。我们使用调查抽样方法、声学遥测技术和分子遗传学来量化港湾海豹（Phoca vitulina）对数量减少的银大麻哈鱼（O. kisutch）洄游群体的捕食量，并确定是否有些海豹捕食的鲑科鱼类数量比其他海豹多得多。基于总共759.5小时观察的概率样本，我们估计在2002年秋季为期84天的时间里，海豹在俄勒冈州一个18.9公里长的河口研究区域的白天时段捕食了1161条成年鲑科鱼类（95%置信区间 = 503 - 1818条鲑科鱼类）。通过声学遥测阵列对56只海豹进行同步追踪表明，一小部分有标记的海豹（12.5%）表现出与专门捕食鲑科鱼类一致的行为。这些海豹大部分时间都在研究区域的河流部分活动，而且夜间活动时间占比相对于白天来说不成比例地更多。对从11份海豹粪便样本中回收的116个鲑科鱼类残骸进行的遗传分析表明，银大麻哈鱼约占鲑科鱼类总捕食量的一半。尽管存在相当大的不确定性，但综合结果使我们推断，海豹捕食了估计的银大麻哈鱼产卵前种群数量的21%（范围 = 3% - 63%）。我们推测，大部分捕食行为发生在夜间的上游区域，且是由当地相对较少一部分海豹群体所为。了解鳍足类动物捕食的程度和性质，可以为风险评估以及其他旨在帮助太平洋西北地区鲑科鱼类保护和恢复的建模工作提供重要信息。这种了解还可能有助于为旨在减少鳍足类动物捕食对鲑科鱼类影响的管理行动提供参考，这些行动可能从短期的致死性捕杀计划到长期的生态系统恢复和保护工作不等。
