Migration and escapement of silver eel males, Anguilla anguilla , from a southwestern European river

• Published in: Ecology of Freshwater Fish
• Main Authors: Monteiro, Rui Miguel, Domingos, Isabel, Almeida, Pedro Raposo, Costa, José Lino, Alexandre, Carlos Manuel, Quintella, Bernardo Ruivo
• Other Authors: PhD Grant attributed to RM Monteiro, Postdoctoral grant attributed to CM Alexandre, Habitat restoration for diadromous fish in river Mondego, Strategic project granted to MARE research centre, COASTNET - Portuguese coastal monitoring network
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Anguilla anguilla
• Online Access: http://dx.doi.org/10.1111/eff.12545; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Feff.12545; https://onlinelibrary.wiley.com/doi/pdf/10.1111/eff.12545; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/eff.12545

Abstract The catadromous life cycle of the European eel encompasses a spawning migration to the Sargasso Sea. Prior to their migration, eels develop a silver coloration being referred to as “silver eels.” Due to the dramatic European eel recruitment decline, it is crucial to quantify silver eel escapement to evaluate the success of measures taken under Eel Management Plans (Regulation EC (1100/2007)). Thus, the percentage of silver eels escaping from the River Mondego (Portugal) was estimated during two consecutive spawning seasons (2014–2016) and their migratory behaviour was studied. Thirty‐six male silver eels were tagged with acoustic transmitters and their downstream migration was tracked using automatic receivers deployed at four locations along the river course, from the first impassable obstacle up to the river mouth (67 km). Among the tagged eels, 15 (42%) escaped to the sea. In both years, individuals displayed faster migration speed in the downstream reaches of the river. BRT (“Boosted Regression Trees”) models were used to explain downstream migration and escapement of silver eels. The analyses revealed that the downstream migration is triggered by several environmental variables with water conductivity as the most influential predictor. Escapement of eels from the estuary occurred a few hours after their arrival and was primarily explained by the offshore wind intensity, which promotes a current in the coast that may favour their transport to the open sea. These findings contribute to a better understanding of silver eel migration in southern latitudes and highlight and reinforce the need to monitor spawner escapement.