Hydropower expansion is increasingly responsible for connectivity and biodiversity loss in freshwater ecosystems. The Amazon basin, which supports the highest level of freshwater biodiversity globally, faces such unplanned expansion. Here, we demonstrate and quantify the impacts of two major hydroelectric dams on the Madeira River on the trans-Amazonian movements of one apex predatory catfish (Brachyplatystoma rousseauxii) performing the longest migration known in freshwaters. Using otolith microchemistry, we show that above the dams, the former basin-wide homing migration between the breeding grounds in the upper Madeira and the nursery in the Amazon estuary has now been replaced by residency. We found evidence suggesting downstream migration of juvenile fish past dams into the Amazon estuary and that some of them home back to the Madeira. However, we did not find evidence that the fish homing back from the estuary can access their breeding grounds in the upper Madeira; they remain blocked below the dams. Our results provide undisputable evidence that the conservation of the species primarily requires the reestablishment of connectivity with the construction of efficient fishways.

中文翻译：

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水电站大坝对巨型鲶鱼跨亚马逊洄游的定量影响


水电扩建对淡水生态系统的连通性和生物多样性丧失负有越来越大的责任。亚马逊流域支持着全球最高水平的淡水生物多样性，却面临着这种计划外的扩张。在这里，我们展示并量化了马德拉河上的两个主要水电站大坝对一种顶级掠食性鲶鱼 （Brachyplatystoma rousseauxii） 跨亚马逊运动的影响，这种鲶鱼在淡水中进行了已知的最长的迁徙。使用耳石微化学，我们表明，在大坝上方，以前在马德拉上游的繁殖地和亚马逊河口的苗圃之间的全流域归巢迁徙现在已经被居住所取代。我们发现的证据表明，幼鱼向下游洄游，通过大坝进入亚马逊河口，其中一些鱼回到了马德拉河。然而，我们没有发现证据表明从河口归巢的鱼可以进入它们在马德拉上游的繁殖地;它们仍然被堵在大坝下方。我们的结果提供了无可争辩的证据，表明该物种的保护主要需要通过建设高效的鱼道来重建连通性。