Glahn J.F., D.S. Reinhold & Sloan C.A. 2000.
Recent population trends of Double-crested Cormorants wintering in the delta region of Mississippi: responses to roost dispersal and removal under a recent depredation order.
Waterbirds, 23(1): 38 - 44
ABSTRACT - The purpose of this study was to examine recent trends in cormorant wintering populations and their economic impact in the delta region of Mississippi and to examine the response of these populations to management efforts directed at reducing their predation on channel catfish (Ictalurus punctatus). We monitored Double-crested Cormorant (Phalacrocorax auritus) populations in the delta region of Mississippi through the use of midwinter ground counts and aerial surveys during the winters of 1995-96 through 1998-99 and surveyed the reported take of cormorants by catfish farmers in the region under the recently-enacted Cormorant Depredation Order. This order issued by the U.S. Fish and Wildlife Service in March, 1998 allowed catfish farmers in the region to kill unlimited numbers of cormorants seen causing depredations at their farms. Despite roost dispersal programs and continued harassment of birds at farms, cormorant populations have significantly increased and based on ground counts have doubled from approximately 32,000 birds to more than 64,000 birds between 1995 and 1999. Mid-winter ground counts and aerial counts were highly correlated and the best linear prediction of ground counts (Y) from aerial counts (b) took the form Y = 1.55 b, (Y-intercept = 0 ). Roost dispersal programs continue to have the desired effect of shifting birds away from areas of highest catfish concentration, but these effects are temporary at best. However, without such programs, the impact of cormorant depredations on the catfish industry in 1997-98 and 1999-98 probably would have more than doubled compared to previous years. Catfish farmers in the delta region of Mississippi reported taking more cormorants under the Cormorant Depredation Order than previously reported under past depredation permits issued to individual farmers. The reported take of at least 9,557 birds by Mississippi catfish Farmers had no apparent impacts on wintering populations during 1998-99. Further monitoring of cormorant wintering populations over more of their wintering range is recommended.