Data from: The origins of Atlantic salmon (Salmo salar L.) re-colonizing the River Mersey in northwest England

By the 1950s, pollution had extirpated Atlantic salmon in the river Mersey in northwest England. During the 1970s, an extensive restoration program began and in 2001, an adult salmon was caught ascending the river. Subsequently, a fish trap was installed and additional adults are now routinely sampled. In this study, we have genotyped 138 adults and one juvenile salmon at 14 microsatellite loci from across this time period (2001–2011). We have used assignment analysis with a recently compiled pan-European microsatellite baseline to identify their most probable region of origin. Fish entering the Mersey appear to originate from multiple sources, with the greatest proportion (45–60%, dependent on methodology) assigning to rivers in the geographical region just north of the Mersey, which includes Northwest England and the Solway Firth. Substantial numbers also appear to originate from rivers in western Scotland, and from rivers in Wales and Southwest England; nonetheless, the number of fish originating from proximal rivers to the west of the Mersey was lower than expected. Our results suggest that the majority of salmon sampled in the Mersey are straying in a southerly direction, in accordance with the predominantly clockwise gyre present in the eastern Irish Sea. Our findings highlight the complementary roles of improving water quality and in-river navigability in restoring salmon to a river and underlines further the potential benefits of restoration over stocking as a long-term solution to declining fish stocks.

至20世纪50年代，污染已导致英格兰西北部默西河（Mersey）中的大西洋鲑鱼（Atlantic salmon）彻底绝迹。20世纪70年代，当地启动了大规模的鲑鱼种群修复工程；2001年，科研人员捕获了一条溯河洄游的成年大西洋鲑鱼。此后，研究团队布设了鱼类诱捕装置，如今会常规采集额外的成年个体样本。本研究对2001至2011年这一时间段内的138条成年大西洋鲑鱼与1条幼鲑，开展了14个微卫星位点（microsatellite loci）的基因分型分析。我们采用基于新近编制的泛欧洲微卫星基线数据集的个体归属分析方法，以确定这些鲑鱼最可能的起源区域。进入默西河的鲑鱼似乎源自多个种群：按不同分析方法测算，有45%至60%的个体被归属到默西河以北紧邻的地理区域的河流，涵盖英格兰西北部与索尔威湾（Solway Firth）流域；另有相当数量的个体源自苏格兰西部、威尔士以及英格兰西南部的河流。不过，源自默西河以西邻近河流的个体数量低于此前预期。研究结果表明，在默西河采集到的绝大多数鲑鱼为向南洄游的迷路个体，这与爱尔兰海（Irish Sea）东部存在的主导顺时针环流格局相符。本研究结果凸显了改善水质与河道通航条件在鲑鱼种群恢复中的互补作用，并进一步证实：作为应对鱼类种群衰退的长期解决方案，栖息地修复相较于人工放流具有显著的潜在优势。