Estimation of production and long-term changes in the population of European eel Anguilla anguilla (L.) in an Irish lake

Monitoring of yellow-phase and silver-phase Anguilla anguilla during their continental life history is necessary for evaluation of stock recovery measures. Eel population data for an Irish lake (Lough Sheelin) were compiled for the period 1993-2014. Catch data from 2009 to 2014 provided minimum estimates of recent silver eel production ranging annually from 0.79 to 1.84kg/ha. Long-term changes in yellow eel abundance and silver eel size structure were assessed as part of a fishery monitoring programme. Yellow eel catch per unit effort (CPUE) in the lake (from longline surveys) was considerably higher in the 1990s (52.2-62.1eels/100hooks) than 2002-2008 (1.9-15.8eels/100hooks). Conversely, during 1993-2014, the mean size of silver eels migrating from the lake increased significantly (p<.001), from 659mm to 838mm. The results suggest that in the absence of direct yellow eel abundance data, interannual variation in silver eel size structure may be a useful monitoring tool for local eel stocks as part of Eel Management Plans (EMP's).