U.S. Department of Agriculture: Animal and Plant Health Inspection Service
Date of this Version
September 2000
Abstract
Aquaculture has expanded rapidly in the Southern United States during the past two decades, especially the cultivation of catfish, crawfish, and bait fish. These fish usually are cultivated on farms with extensive systems of large shallow ponds that are highly susceptible to predation by birds. Double-crested cormorants (Phalacrocorax auritus ), American white pelicans (Pelecanus erythrorhynchos ), wading birds (e.g., Ardea alba, Ardea herodius ), and scaup (Aythya spp. ) are among the birds most frequently implicated. Well-documented problems associated with cormorant predation on catfish farms have coincided with the increase of this industry and the rapid growth of cormorant breeding populations on northern breeding grounds. From 1995 to 1998, the number of cormorants spending the winter in the catfish production region of Mississippi has more than doubled and now exceeds 60,000 birds. Also in 1998, cormorants were discovered breeding in Mississippi and Arkansas for the first time in decades. Without human intervention, breeding populations in the Great Lakes will likely continue to increase, resulting in more habitat destruction, competition with other colonial waterbirds, competition with sport fishermen, and depredations on southern aquaculture farms. The nature and expansiveness of southern aquaculture and the continued growth of cormorant populations limit options for managing depredations on aquaculture farms. Most efforts rely on devices designed to frighten them from ponds and roosts, although the effectiveness of this strategy is limited and, due to expanding habitat utilization by cormorants, is becoming increasingly difficult to implement. In the long-term, further research may lead to the development of barriers, new fish-culturing practices, or other techniques that may help alleviate problems in certain situations. However, no such strategies seem promising at this time and may be limited in the future by the rapid proliferation of this species. In the short term, lethal control strategies under the current cormorant depredation order may need to be implemented to their fullest extent at aquaculture facilities and may need to be expanded to roosting sites to reinforce harassment strategies. Authority should also be pursued to manage southern breeding colonies at levels compatible with aquaculture to forestall future depredation problems. However, such localized population control efforts are unlikely to affect continental or flyway populations, and problems are likely to grow as long as the interior population grows. Managers should consider managing cormorant populations on a flyway basis, which will require setting biologically and socially acceptable population goals and evaluating management options for achieving these goals. Construction of a realistic, deterministic population model for cormorants would facilitate these ends. Increased dialog among public agencies and private organizations concerned about the management and conservation of cormorants is critical to the development of a realistic and effective plan for managing the depredations caused by this species.