Proceedings of the Vertebrate Pest Conference

Several North American waterbird species were negatively affected by compromised environmental quality by the mid-twentieth century. Double-crested cormorant populations responded to increased environmental regulations in the United States in the early 1970s. The abundance of cormorants wintering in southern states (especially Alabama, Arkansas, Lousiana, and Mississippi) increased concurrently with a marked increase in catfish, crawfish, and bait fish production in these states since 1980, thus increasing regional concern regarding production losses to these industries. Cormorants wintering in Mississippi have increased nearly 225% since 1990. Food habit studies, bioenergetic predictions, and captive-bird foraging experiments indicate that individual cormorants consume approximately 0.5 to 0.7 kg (1 to 1.5 pounds; i.e., about 10 fingerlings) of catfish fingerlings per day. Although no present management techniques permanently redistribute cormorants, dispersal of night roosts remains the most effective method to temporarily deter cormorants from primary aquaculture areas. Ongoing investigations will improve our understanding of cormorant impacts to catfish production, and the annual movement patterns and population biology of North American cormorants. Given concerns regarding cormorant impacts to commercial and recreational fisheries in the United States, management objectives should highlight minimized impacts to economic and recreational opportunities, rather than target populations of breeding and/or wintering double-crested cormorants.