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

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