Fine‐scale swimming movement and behaviour of female silver eels,Anguilla dieffenbachii,within a lake affected by hydro‐power generation

Lake Manapouri (South Island, New Zealand) maintains the country’s largest hydroelectric scheme (700 MW). During their seaward migration, silver eel Anguilla dieffenbachii Gray in this lake are attracted to the power station intake, as well as the natural outlet. To understand the behaviour of such eels, 210 female eels were tagged with acoustic transmitters between 2005 and 2010. Swimming speeds of tagged eels averaged 2.0 km/hr, and swimming depths were deeper during daytime than at night. Silver eels from sites upstream of Lake Manapouri tended to spend more time exploring Lake Manapouri than locally caught eels, and a higher proportion entered the power station intake. Almost 20% of tagged eels did not leave the lake during the year they were tagged. Eels typically showed extensive and complex patterns of movement before emigrating, including multiple passes across the power station intake or the natural outlet.