Depredation of Catfish by Double-crested Cormorants at Aquaculture Facilities in Oklahoma

Oklahoma has about 324 ha of surface water in catfish (Ictalurus spp.) production. The state also supports a large number of migrating and wintering piscivorous birds, particularly double-crested cormorants (Phalacrocorax auritus). To address concerns of aquaculture facility operators regarding loss of fish to cormorants, we asked 11 operators to conduct regular counts of piscivorous birds at each facility. These data were used to determine factors affecting cormorant density at facilities and to estimate amount of catfish lost to cormorant depredation. Cormorant density (birds/ha/day) was positively correlated with surface area of water in production at facilities <10 ha (r = 0.621, P = 0.004) and negatively correlated with percentage of forested shoreline at each facility (r = -0.518, P = 0.016). Distance to nearest major reservoir or river was not significantly correlated with cormorant densities. To estimate depredation, we assumed a daily intake of 0.4 kg of fish per cormorant and used the average number of birds counted at participating facilities. Cormorants consumed an estimated 7,196 + 8,729 kg ( x + SE) of catfish, valued at $13,672-$36,195 (depending on size offish consumed), or about 3-7% of Oklahoma catfish sales in 1993. Pages 34-37 in R.E. Masters and J.G. Huggins, eds. Twelfth Great Plains Wildl. Damage Control Workshop Proc, Published by Noble Foundation, Ardmore, Okla.