Fishway attraction efficiency during upstream and down-stream migration: field tests in a small hydropower plant with run-of-the-river configuration

Producción CientíficaUnderstanding fishway attraction is one of the main open challenges in fishways research, and unraveling the mechanisms and relationships that trigger it is crucial to improve the performance of fishways. Furthermore, attraction is usually understood in terms of upstream migration; however, taking into account the possible bidirectional use of fishways, it is equally important to study this phenomenon during downstream migration, although this is usually considered negligible. Therefore, this study aims to advance our understanding of fishway attraction efficiency by considering both upstream and downstream movements in a key small hydropower plant scheme in the Iberian Peninsula. To achieve this, one of the most common Iberian fish species, the Iberian barbel (Luciobarbus bocagei, Steindachner), was monitored via telemetry in a stepped fishway. The studied fishway, considering the specialized literature, would be classified as poor in attraction, i.e., difficult to find due to its low competing discharge and the long distance between the main river flow and both fishway entrances. Fish were PIT tagged and released in different upstream and downstream locations and on different dates. The results showed that a significant proportion of the tagged barbels was able to successfully locate the fishway from both sides, in spite of the mentioned localization drawbacks, with inter-annual variability and with repeated events throughout the years. This suggests that even a fishway with a theoretical poor attraction can still be localized by fish, allowing their use as a two-way migration route, at least with species and HPP schemes such as those already studied

Presence of invasive alien species (IAS) in impounded waters of Navarre (Spain) using multi-mesh gillnets

The introduction of invasive alien species (IAS) is a severe problem in ecosystems worldwide, heavily impacting biodiversity and especially endemic species. This situation is especially worrying in the Iberian Peninsula, since Spain and Portugal¿s rivers and lakes host an outstanding richness of endemic freshwater species. Ignorance about IAS presence and distribution is a serious problem that hampers its management. Regarding invasive fish species, difficulties in sampling and studying the ichthyofauna of lentic and deep waters, where many IAS inhabit, comprise some of the reasons for this lack of knowledge. In this study, we sampled the fish community of ten impounded waters in Navarre (Ebro River Basin, Spain) using multi-mesh gillnets. Four sampling points were dams located in rivers, and the remaining points were ponds. One of these ponds had a direct connection with a water channel, and another was found in a flood plain, so it connects with a nearby river in floods. The remaining ponds did not have a direct connection to any major river. A total of 14 fish species were detected (9 of which were IAS (64.3%)), with 3383 specimens collected (56% IAS). Only one of the analyzed dams did not contain IAS. Numerically, the most abundant fish was the exotic bleak (Alburnus alburnus) (almost 44% of the captures), followed by the native Ebro nase (Parachondrostoma miegii) (23.4%)