Hydrometric and Meteorological Factors Affecting the Seaward Migration of Silver eels (Anguilla anguilla, L.) in the Lower River Shannon

European eels, Anguilla anguilla, L., are captured in coghill nets at three commercial weirs on the Irish River Shannon during their autumn/winter seaward migration. The variations in daily silver eel catches were analysed in relation to environmental conditions, especially hydrometric and meteorological factors. Three multivariate environmental axes were distinguished with which daily eel catches could be correlated. The relative importance of various hydrometric, meteorological and temporal (seasonality, lunar phase) factors was identified, showing how hydrological and meteorological factors generally obscure the underlying lunar periodicity of the silver eel migrations at Killaloe.