The River Shannon silver eel fisheries : variations in commercial and experimental catch levels i

Management of the eel fisheries of the River Shannon, Ireland’s largest river system, has involved van ous stock enhancement measures since 1959. Declining natural recruitmenr levels have limited the effecriveness of stocking programmes for nearly two decades. Observations on declining yellow eel stocks in several major lakes have been supported by the results of studies undertaken annually on the seaward migrating silver eel populations from 1992 to ‘99. A decline in the combined silver eel yield from a series of commercial and experimental fishing sites has occurred, despite increases in fishing effort. Changes in silver ccl length-frequency distributions and sex ratios appear to be linked to declining stock levels. Silver eel migration patterns vary within the catchment and in upper Shannon catchment sites a lunar periodicity is normally evident in the autumn/winter silver eel movements. Silver eel migra non in the loxver reaches of the river system is strongly influenced by variations in discharge due to river regulation for hydroelectricity generation. Despite the decline in stock levels, the results of observations at experimental sites and on commercial ccl weir operations suggest that improvements in silver eel fish ing methods could result in significantly greater catch levels.