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 regurgitates and the stomach contents of adult birds. Non-breeding coastal birds consumed mostly marine fish while breeding birds were found to 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 greater, more varied or more predictably exploitable food supplies in certain freshwaters at certain times. In years when Roach and Perch were much less abundant in Lough Neagh, diet at the breeding colony reverted to an increased proportion of marine fish and even a high Salmon smolt run on an inland river was practically neglected. In recent years the impact of Cormorants on fish in this river close to the breeding colony has declined and a number of reasons for this are discussed. Nevertheless, Cormorants visit the river all the year round and their impact on older Salmon parr is likely to be particularly significant.

Warke G.A. & Day K.R., ARDEA 83 (1): 157-166.