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 lifecycles. 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, turbinesor specific solutions such as bypass systems.2. So far, studies and scientific discussions concerning bidirectional movementsthrough fishways are scarce and focused on large dams and reservoirs, mainlywith large migratory species such as salmonids, rather than smaller facilities andlesser known species.3. This study investigated bidirectional movements through a small run-of-the-riverhydropower plant with a pool-and-orifice type fishway, using the Iberian barbel(Luciobarbus bocagei), a potamodromous cyprinid, as the target species. Passiveintegrated transponder and radio tracking data were collected over 4 years andcombined to characterize upstream and downstream movements. The studyfocused primarily on fish movements through the fishway, but also estimated themultiple 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 fishreturning over the years.5. The documented movements and observations indicate that fishways can serveas an effective bidirectional migration corridor for fish, potentially enhancing theconservation efforts for potamodromous species. This study supports thedecision to use fishways as an overall mitigation tool to reduce the impact ofsmall hydropower facilities on fish.