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

Abstract

Abstract 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. 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. 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. 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 serve as 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.