CHANGES IN ABUNDANCE OF CYPRINID AND PERCID PREY AFFECT RATE OF PREDATION BY CORMORANTS PHALACROCORAX-CARBO-CARBO ON SALMON SALMO-SALAR SMOLT IN NORTHERN-IRELAND

Cormorant diet is described from the analysis of pellets, fledgling re gurgitates and the stomach contents of adult birds. Non-breeding coast al birds consumed mostly marine fish while breeding birds were found t o feed mostly on freshwater fish species. The long distances travelled to inland feeding sites while breeding suggested that the high energy investment in commuting could be traded against the rewards of greate r, more varied or more predictably exploitable food supplies in certai n freshwaters at certain times. In years when Roach and Perch were muc h less abundant in Lough Neagh, diet at the breeding colony reverted t o an increased proportion of marine fish and even a high Salmon smelt run on an inland river was practically neglected. In recent years the impact of Cormorants on fish in this river close to the breeding colon y has declined and a number of reasons for this are discussed. Neverth eless, Cormorants visit the river all the year round and their impact on older Salmon parr is likely to be particularly significant.