In 2011, a vertical‐slot fish pass was built at the Coimbra Açude‐Ponte dam (Mondego River, Portugal), approximately 45 km upstream from the river mouth. The performance of this infrastructure for sea lamprey passage was evaluated between 2011 and 2015 using several complementary methodologies, namely radio telemetry [conventional and electromyogram (EMG)], passive integrated transponder (PIT) telemetry and electrofishing surveys. During the study period, the electrofishing revealed a 29‐fold increase in the abundance of larval sea lamprey upstream of the fish pass. Of the 20 radio‐tagged individuals released downstream from the dam, 33% managed to find and successfully surpass the obstacle in less than 2 weeks, reaching the spawning areas located in the upstream stretch of the main river and in one important tributary. Fish pass efficiency was assessed with a PIT antenna installed in the last upstream pool and revealed a 31% efficiency, with differences between and within migratory seasons. Time of day and river flow significantly influenced the attraction efficiency of the fish pass, with lampreys negotiating it mainly during the night period and when discharge was below 50 m3 s−1. Sea lampreys tagged with EMG transmitters took 3 h to negotiate the fish pass, during which high muscular effort was only registered during passage, or passage attempts, of the vertical slots. The use of complementary methodologies provided a comprehensive passage evaluation for sea lamprey, a species for which there is a considerable paucity of valuable data concerning behavioural, physiological and environmental influences on obstacle negotiation. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

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Movement of sea lamprey through a vertical-slot fishway (built at the Coimbra dam, in central Portugal) was continuously monitored between 2013 and 2016 by a video recording system. Visual count data were used to quantify the overall successful movements and identify seasonal and circadian patterns of fishway use. Explicative models (Boosted Regression Trees) were used to study the relationship between frequency of successful movements during the species migration peak and environmental variables. The aim of the study was to identify predictors that may be related with successful sea lamprey upstream migration through the fishway. Collected information was used to support further management recommendations for optimizing the fishway performance. During the 4-year study, near 50,000 lampreys successfully negotiated the Coimbra dam fishway reaching the upper stretch of river Mondego.Migratory peak occurred between April and May with an increase in passages during the night period (between 11 p.m. and 6 a.m.). It was observed an increase in use frequency that was related with the combined effect of flow and temperature. Higher passages were achieved when Coimbra dam discharge flows are lower than 100 m 3 /s and temperature between 15 and 19°C. Flow discharges higher than 150 m 3 /s seemed to inhibit successful sea lamprey passage. In dry years, when flows are almost constantly lower than 50 m 3 /s, temperature was the most important factor influencing fishway use.

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