Concurrent Sessions D: Fish Passage Around the World - I - Seasonal and Diel Movement Patterns of Yellow Eels Migrating Through a Fish Lift

• Main Authors: Santos, José Maria, Oliveira, João, Rivaes, Rui, Pizarro, Raul, Pádua, João, Ferreira, Teresa
• Format: Text
• Language: unknown
• Published: ScholarWorks@UMass Amherst 2013
• Subjects: Anguilla anguilla; European eel
• Online Access: https://scholarworks.umass.edu/fishpassage_conference/2013/June25/52; https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1320&context=fishpassage_conference

The blockage of upstream movements by high dams and subsequent reduction in availability of habitat has been reported as a key factor contributing to population decline of inland stocks of the European eel Anguilla anguilla. Although a significant amount of research has been carried out on the migration of descendent silver eels, much less information is available on the migratory ecology of upstream yellow eels and also on their ability in using fish lifts, the most cost-effective mitigation measures for high dams. This study aims to determine i) the seasonal and daily upstream movement patterns; ii) the environmental factors associated with the triggering of the upstream migration and iii) the ability of yellow eels in using fish lifts during their upward migration. Upstream eel passage was continuously monitored over an annual cycle in the fish lift built at the Touvedo dam on the Lima River, north Portugal. Monitoring consisted in the use of an automatic video-recording system in combination with monthly electrofishing samplings undertaken in a 200-m river segment immediately below the dam. Parallelly, hydraulic characterization of the entrance collection system was performed by an Acoustic Dopler Velocimeter (ADV) to assess species capacity to negotiate existing velocities at the entrances and within the circuit. A total of 1207 eels were transferred by the lift, of which 98.4% passed during the summer and in the beginning of autumn. Movements occurred independently of time of day. Of the environmental factors considered, only moon phase (-) and daily accumulated rainfall (+) correlated significantly with daily numbers of eel. Overall the fish lift was found to be non-selective for the eel, however size-related differences were detected as the smallest size-class (< 10 cm TL) was under-represented in the facility relatively to the river downstream. The use of fish lifts by eels may be improved by reducing the free gap between retention screens and providing adequate water velocities in the entrances and within the attraction circuit.