Riverine dams and weirs present silver eels with multiple migration routes during their downstream migrations. In relation to dams, understanding route selection is important for estimating silver eel escapement, especially where mortality rates vary among routes. On the lower River Shannon, Ireland, a water-regulating weir presents silver eels with two potential migration routes, the natural river channel and a headrace canal leading to a hydropower station. Route selection at the weir was investigated using a dual-frequency identification sonar (DIDSON) and replicated mark–recapture experiments. The proportion of eels migrating via the headrace canal was strongly related to the proportion of total flow diverted to that route (R2 = 0.827, P < 0.001), suggesting that eel route selection was passive. The active swimming speeds of eels (median = 0.16 m s−1), observed with the acoustic camera, did not greatly exceed water velocity and further suggested that eels were largely carried by the current. Knowledge of the relationship among flow, water velocity and eel route selection highlighted the potential to strategically alter hydropower-generating protocols to maximise silver eel passage via safer routes, and enhance survival.

中文翻译：

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使用声学相机评估调水堰的银鳗（Anguilla anguilla）路线选择

河流大坝和堰在下游迁徙过程中呈现出具有多条迁徙路线的银鳗。对于大坝，了解路线选择对于估计银鳗逃逸很重要，尤其是在死亡率因路线而异的情况下。在爱尔兰香农河下游，一个调水堰为银鳗提供了两条潜在的迁徙路线，一条天然河道和一条通往水电站的引水渠。使用双频识别声纳 (DIDSON) 和复制标记-重新捕获实验研究了堰的路线选择。通过引水渠迁移的鳗鱼比例与转向该路线的总流量比例密切相关（R2 = 0.827，P < 0.001），表明鳗鱼路线选择是被动的。用声学相机观察到的鳗鱼的主动游泳速度（中值 = 0.16 ms-1）并没有大大超过水速，并进一步表明鳗鱼主要由水流携带。流量、水速和鳗鱼路线选择之间关系的知识突出了战略性地改变水力发电协议的潜力，以通过更安全的路线最大限度地提高银鳗的通过率，并提高生存率。