Data from: Water, water everywhere: environmental DNA can unlock population structure in elusive marine species

Determining management units for natural populations is critical for effective conservation and management. However, collecting the requisite tissue samples for population genetic analyses remains the primary limiting factor for a number of marine species. The harbor porpoise (Phocoena phocoena), one of the smallest cetaceans in the Northern Hemisphere, is a primary example. These elusive, highly mobile small animals confound traditional approaches of collecting tissue samples for genetic analyses, yet their nearshore habitat makes them highly vulnerable to fisheries bycatch and the effects of habitat degradation. By exploiting the naturally shed cellular material in seawater and the power of next generation sequencing, we develop a novel approach for generating population-specific mitochondrial sequence data from environmental DNA (eDNA) using surface seawater samples. Indications of significant genetic differentiation within a currently recognized management stock highlights the need for dedicated eDNA sampling throughout the population’s range in southeast Alaska. This indirect sampling tactic for characterizing stock structure of small and endangered marine mammals has the potential to revolutionize population assessment for otherwise inaccessible marine taxa.确定自然种群的管理单元，是开展高效保护与管理工作的核心前提。然而，针对诸多海洋物种而言，采集种群遗传分析所需的组织样本，始终是制约研究推进的首要瓶颈。港湾鼠海豚（harbor porpoise, *Phocoena phocoena*）作为北半球体型最小的鲸类之一，正是这类研究困境的典型代表。这类行踪诡秘、移动能力极强的小型鲸类，使得传统组织样本采集方法难以适用于其遗传分析；但它们的近岸栖息环境，又使其极易遭受渔业副渔获物威胁，同时面临生境退化带来的负面影响。本研究利用海水中自然脱落的细胞物质，并结合下一代测序（next generation sequencing）技术，开发了一种全新方法：通过采集表层海水样本，从环境DNA（environmental DNA, eDNA）中获取种群特异性的线粒体序列数据。研究在当前已划定的管理种群内检测到显著的遗传分化信号，这提示我们有必要在阿拉斯加东南部的整个种群分布范围内开展专门的eDNA采样工作。这种用于解析小型且濒危海洋哺乳动物种群结构的间接采样策略，有望为原本难以开展调查的海洋类群的种群评估带来革命性变革。