Predation of Fish in Farm Dams by Cormorants, Phalacrocorax Spp.

Abstract

The effect of cormorants on the survival of native warm-water fishes in farm dams in south-western New South Wales was monitored during 1979 and 1980. Three species of cormorants frequented the dams: the great cormorant Phalacrocorax carbo, the little pied cormorant P. melanoleucos, and the little black cormorant P. sulcirostris. In dams fished by cormorants, more than 50% ofthe fish were consumed unless abundant alternative prey, in this case crayfish Cherax destructor, was present. Dams stocked with few fish (approximately 150 ha-1) were less commonly fished than those stocked with many fish (more than 450 ha-1). The majority of dams in the study area were fished by cormorants, which were present from midwinter to midsummer in both years. The results, and an examination of aspects of cormorant biology and methods used to prevent birds eating fish at hatcheries, indicated that buffer populations of crustaceans and low fish stocking rates are suitable methods for minimizing predation of fish in farm dams by cormorants.