When barriers to migration are removed, anadromous fishes from other rivers may colonize newly accessible habitat or landlocked forms of the species may resume anadromy if conditions allow. For example, two large hydroelectric dams on the Elwha River, Washington, were removed between 2011 and 2014 to restore populations of Pacific salmon Oncorhynchus spp. after a century of isolation. Immediately prior to and following dam removal (2010–2017), upstream-migrating adult Sockeye Salmon Oncorhynchus nerka were sampled, and DNA was extracted and compared with samples from the local Lake Sutherland population (above the lower dam’s former location) and a coastwide genetic baseline to determine the probable origin of each fish. Genetic analysis indicated that none of the 45 Sockeye Salmon sampled had originated from the local population or other populations nearby in the genetic baseline, and only a single fish originated from the abundant and proximate Fraser River populations. The strays reflected two different sources and processes: 22 were from the west coast of Vancouver Island (all in 2015, when these populations were very abundant and encountered conditions unfavorable for upstream migration in their natal system) and another 22 assigned to more northerly populations, mostly to riverine populations from the Stikine River. Test fishery samples collected in the Strait of Juan de Fuca contained very few fish with assignments similar to these northern rivers. It is not clear whether these individuals originated from the distant riverine populations or from a closer population not in the baseline that resembles them genetically. Taken together, the findings indicate that the genetic composition of any future population in the Elwha River may reflect signatures from diverse sources and subsequent selection in the new habitat.

中文翻译：

---

恢复解剖学还是迷路？艾尔瓦河红鲑鱼的起源

当洄游障碍消除后，来自其他河流的溯河鱼类可能会在新近进入的栖息地定居，或者在条件允许的情况下，该物种的内陆形式可能会恢复溯河。例如，2011 年至 2014 年间，华盛顿州艾尔瓦河上的两座大型水电站被拆除，以恢复太平洋鲑鱼Oncorhynchus spp. 的种群。经过一个世纪的孤立。在大坝拆除之前和之后（2010-2017 年），上游迁徙的成年红鲑Oncorhynchus nerka采样，提取 DNA 并与来自当地萨瑟兰湖种群（位于下游大坝以前的位置上方）和沿海遗传基线的样本进行比较，以确定每条鱼的可能来源。遗传分析表明，采样的 45 条红鲑鱼中没有一条来自当地种群或遗传基线附近的其他种群，只有一条鱼来自丰富且邻近的弗雷泽河种群。这些流浪者反映了两种不同的来源和过程：22 只来自温哥华岛西海岸（都是在 2015 年，当时这些种群非常丰富，并且在其出生系统中遇到了不利于上游迁移的条件），另外 22 只来自更北的种群，主要是来自斯蒂金河的河流种群。在胡安德富卡海峡收集的测试渔业样本中含有与这些北部河流相似的鱼类很少。目前尚不清楚这些个体是来自遥远的河流种群还是来自更近的种群，而不是在基因上与它们相似的基线。综上所述，研究结果表明，艾尔瓦河中任何未来种群的遗传组成可能反映了来自不同来源的特征以及随后在新栖息地的选择。