Bidirectional connectivity in fishways: A mitigation for impacts on fish migration of small hydropower facilities

Abstract

1. Most freshwater fish need to move freely through rivers to complete their life cycles. Thus, river barriers (e.g. dams, culverts and gauging stations) may delay, hinder or even block their longitudinal movements, affecting fish conservation.The most widespread solution to allow upstream fish migration are fishways, whereas downstream migration is basically facilitated through spillways, turbines or specific solutions such as bypass systems.2. So far, studies and scientific discussions concerning bidirectional movements through fishways are scarce and focused on large dams and reservoirs, mainly with large migratory species such as salmonids, rather than smaller facilities and lesser known species.3. This study investigated bidirectional movements through a small run-of-the-river hydropower plant with a pool-and-orifice type fishway, using the Iberian barbel (Luciobarbus bocagei), a potamodromous cyprinid, as the target species. Passive integrated transponder and radio tracking data were collected over 4 years and combined to characterize upstream and downstream movements. The study focused primarily on fish movements through the fishway, but also estimated the multiple associated routes of passage.4. The results show diverse fish movements with inter-and intra-annual variability, with several individuals performing bidirectional movements and even some fish returning over the years. The documented movements and observations indicate that fishways can serveas an effective bidirectional migration corridor for fish, potentially enhancing the conservation efforts for potamodromous species. This study supports the decision to use fishways as an overall mitigation tool to reduce the impact of small hydropower facilities on fish.

Searching for the critically endangered European eel in oceanic islands: A pioneer study in the freshwater systems of Madeira, Macaronesia

“…Simultaneously, increasing evidence shows how these obstacles to fish migration including the less considered small onesare responsible for habitat fragmentation, limit fish movement, affect their physical condition and impact the life cycles of a wide array of species (Acou et al, 2008;Belletti et al, 2020;Clavero & Hermoso, 2015;OSPAR, 2022;Teichert et al, 2022). Recently, there has been an increase in the removal of obsolete obstacles and the construction of eel passes (some with reduced costs such as bristles and tiles) (Bravo-C ordoba et al, 2023;Kerr et al, 2015;Laffaille et al, 2005;Sun et al, 2021;Tamario et al, 2019;Vowles et al, 2015). In Madeira, artificial structures were constructed years ago to prevent and mitigate the primary hazard to human safety in the regionfloods (Couto et al, 2012;Rosa et al, 2022).…”

Can't pass or won't pass: the importance of motivation when quantifying improved connectivity for riverine brown trout Salmo trutta

“…Experimental translocation of territorial wild birds and mammals has been used to study the impact of anthropogenic fragmentation and the functional connectivity of terrestrial landscapes during homing (Bakker & Van Vuren, 2004;Desrochers et al, 2011;Valente et al, 2019). Freshwater and marine fishes also perform homing movements after translocation (Gardner et al, 2015;Girard et al, 2007;Huntingford et al, 1998;Lucas & Baras, 2001;Shima et al, 2012;Stott et al, 1963), including during fish pass studies for both up-and downstream migrations (Bravo-C ordoba et al, 2018(Bravo-C ordoba et al, , 2023Celestino et al, 2019;Dodd et al, 2017;Forty et al, 2016;Ovidio et al, 2017Ovidio et al, , 2020Sanz-Ronda et al, 2021;Tummers et al, 2016). However, we are not aware of any experiments, terrestrial, avian, or aquatic, that incorporate both translocated and non-translocated animals (released freely at the same location) to specifically and explicitly quantify the importance of homing motivation during studies on landscape fragmentation or reconnection.…”