Fish pass use by shads ( Alosa alosa L. and Alosa fallax [Lacépède, 1803]): Implications for monitoring and management

Fish pass monitoring is essential to ensure the device's effectiveness as a mitigation measure for river impoundment, guaranteeing longitudinal continuity of rivers, which particularly important diadromous fish that depend on obligatory migrations freshwater reproduction (anadromous) or feeding areas (catadromous) complete their life cycle. The upstream migration anadromous allis (Alosa alosa L.) and twaite fallax Lacépède, 1803) shad in River Mondego, Central Portugal, being monitored at Coimbra Dam since 2013, using visual counts. Statistical models were used evaluate passage identify main environmental variables seem condition behaviour. A total 26,561 recorded this infrastructure during study period (2013–2017), with 96.5% counted between April June. Overall, water temperature flow are predictors consistently influence number pass, although its individual contribution changed years. (Boosted Regression Trees) obtained robust an average explained deviance 0.79 (R2), despite poorer results associated 2015 spawning season, possibly related low adult observed year. Results from contribute better understand dynamics use by Alosa sp. can help conservation management these species through improvement attractiveness and, consequently, overall efficiency devices targeting shads.