Spawner escapement of European eel (Anguilla anguilla) from the River Erne, Ireland

Knowledge of silver eel production and escapement is essential for conservation of the European eel (Anguilla anguilla) stock. Silver eel trap and transport, being undertaken (2009-2012) to mitigate for negative impacts of hydropower on eels in some Irish rivers, was therefore monitored in the River Erne (catchment area 4375 km²). Eel population analyses at an experimental fishing weir involved mark-recapture experiments and sonar (DIDSON) surveys. Silver eel mortality rates at two hydropower stations were assessed by acoustic telemetry. The combined results of these studies enabled estimation of silver eel production and escapement for two migration seasons. For the 2010 season, production and escapement estimates were 42.5 t (1.62 kg·ha^-1) and 38.8 t (1.48 kg·ha^-1), respectively. For the 2011 season, production and escapement estimates were 44.6 t (1.70 kg·ha^-1) and 41.8 t (1.59 kg·ha^-1), respectively. Closure of all commercial eel fisheries and initiation of silver eel conservation fishing in 2009 resulted in 9.36, 19.33 and 25.25 t of silver eels being transported downstream of the hydropower dams in 2009, 2010 and 2011, respectively. The protocols developed in this study can be used to test models being used for eel population management in Ireland.