Abstract
Abstract Black cormorants (Phalacrocorax carbo), little black cormorants (P. sulcirostris), and little pied cormorants (P. melanoleucos) were observed to cause nearly total depredation of the Australian freshwater fish Bidyanus bidyanus, known as silver perch, in four ponds. Survival rates of fry (mean weight, 0.8 g) stocked into three 0.1-ha ponds at 50,000 and 60,000 fish/ha were 0.3%, 0.8%, and 3.5%r, and the survival of fingerlings (mean weight, 69.5 g) stocked into a 0.3-ha pond at 8,000 fish!ha was 0.9%. Little black cormorants and little pied cormorants preyed mainly on small fingerlings (3–75 g); black cormorants took fish from 55 g up to 373 g. The estimated value of fish lost was $A107,000. Gill nets hung vertically in the water and harassment patrols were ineffective in deterring the cormorants. The exclusion of birds by overhead netting, particularly on ponds containing fingerlings, is proposed to prevent future depredation.
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