THE IMPACT OF DOUBLE-CRESTED CORMORANTS ON THE MISSISSIPPI DELTA CATFISH INDUSTRY - A BIOENERGETICS MODEL

A bioenergetics model was constructed and evaluated for estimating Dou ble-crested Cormorant (Phalacrocorax auritus) energy expenditures, foo d demand and impact on the Channel Catfish (Ictalurus punctatus) indus try in the Delta region of Mississippi. Large body mass (mean = 2.27 k g) and higher basal metabolism (115% to 128% of predicted) resulted in an average predicted food demand of 504 g/bird/day (range: 449 to 551 ) from November to March or 22% of body mass. Factoring in population sizes and proportional intake of catfish, Double-crested Cormorants ma y have eaten up to 20 million catfish per winter in 1989-90 and 1990-9 1 or approximately 4% of the estimated standing crop at a replacement cost of $2 million (US$) annually. More than 50% of catfish losses wer e projected to occur in February and March; negligible losses occurred in November.