The Atlantic salmon (Salmo salar) population of the River Minho represents the southern natural distribution edge of the species. In line with the general trend for Atlantic salmon, this population has been declining over the years and is now at a critically low level. With river connectivity compromised by a large dam just 80 km upstream the River Minho's outlet, and an expected deterioration of climatic conditions, it is urgent to increase our knowledge of this population and identify survival bottlenecks that can be addressed. In this study, we used radio and acoustic telemetry to track Atlantic salmon smolts during their migration towards the sea and record both survival rates and possible causes of mortality. The recorded survival for the tagged migrating Atlantic salmon remained below 55% in the three studied years, indicating that the in‐river loss of smolts is likely a strong constraint to this population. From the smolts to which a likely cause of mortality could be attributed (34%), most appear to have been removed from the river (25%), with two confirmed events of bird predation and one of mammal predation. Interestingly, eight tags were recorded moving back upstream, likely indicating predation by larger fish. Increasing predator populations (e.g. cormorants, Phalacrocorax carbo) and invasive predators (e.g. American mink, Neovison vison) lead to elevated predation pressure on this already strained Atlantic salmon population, and further studies quantifying their impact in more detail could prove crucial for future management considerations.

中文翻译：

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生活在边缘的大西洋鲑鱼：Minho河向海迁徙期间的鲑鱼行为和生存

大西洋鲑鱼（Salmo salar）Minho河的种群代表了该物种的南部自然分布边缘。与大西洋鲑鱼的总体趋势一致，这些年来，该种群一直在减少，现在处于极低的水平。由于Minho河出口上游仅80公里处的大型水坝损害了河流的连通性，并且气候条件预计会恶化，因此迫切需要增加我们对这一人口的了解，并确定可以解决的生存瓶颈。在这项研究中，我们使用无线电和声学遥测技术来追踪大西洋鲑鱼向海迁移的过程，并记录其成活率和可能的死亡原因。在所研究的三年中，标记的迁徙大西洋鲑的记录生存率保持在55％以下，表明河蟹的河道损失可能是对该种群的强烈限制。从可能归因于死因的软体动物（34％）中，大多数似乎已从河中移出（25％），其中有两个已确认的鸟类捕食事件和一个哺乳动物捕食事件。有趣的是，记录到八个标签向上游移动，这可能表明被大鱼捕食。捕食者数量不断增加（例如cor，ala（Carbocrocorax carbo）和侵入性捕食者（例如美国水貂，Neovison vison）导致该已经紧张的大西洋鲑鱼种群的捕食压力升高，进一步研究量化其影响可能证明对将来的管理考虑至关重要。