One of the movement barriers that fish populations must overcome for migration success in the upper basin of Tormes river (Salamanca, Spain) is a 20 m high dam. The design of its pool and weir fishway for potamodromous fishes (mostly Iberian barbel—Luciobarbus bocagei—and Northern straight-mouth nase—Pseudochondrostoma duriense) to overcome the obstacle was improved in 2013. The aim of this study was to assess the efficiency of the fishway using FDX passive integrated transponder (PIT)-Tags inserted into the fish and PIT-Tag detection antennas at the fishway. During several sampling events, 7113 barbel and nase individuals were tagged and released at the point of capture along the basin (2538 and 4575 of which were tagged downstream and upstream, respectively). PIT-Tag Detection Antennas close to the top and bottom of the fishway monitored tagged fish continuously for 10 months (from March to December 2017), to analyze the performance of the fishway. Upstream passage efficiency was greater for barbel (60% and 25% for barbel and nase, respectively). Differences in passage efficiency between species may be due to differences in their size. Mean length for barbels attempting to pass was 336 mm (±47 mm) while for nases was 143 mm (±26 mm). Moreover, both the number of attempts to pass and ascend time for nases were higher than for barbels. Entrance efficiency was low (3.5% and 10.8% for barbel and nase, respectively), although 2017 was a very dry year, thus these results are most likely influenced by flow rates. Therefore, the fishway has proved to be functional but is actually poor for efficiency purposes, especially for small fish.

No abstract