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

The purpose of this study was to examine recent trends in cormorant winteri ng populations and their economic impact in the delta region of Mississippi and to examine the response of these populations to management efforts dir ected 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 coun ts and aerial surveys during the winters of 1995-96 through 1998-99 and sur veyed the reported take of cormorants hv catfish farmers in the region unde r the recently-enacted Cormorant Depredation Order. This order issued by th e U.S. Fish and Wildlife Service in March, 1998 allowed catfish farmers in the region to kill unlimited numbers of cormorants seen causing depredation s 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 aeri al counts were highly correlated and the best linear prediction of ground c ounts (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 cormor ant depredations on the catfish industry in 1997-98 and 1999-98 probably wo uld have more than doubled compared to previous years. Catfish farmers in t he delta region of Mississippi reported taking more cormorants under the Co rmorant Depredation Order than previously reported under past depredation p ermits issued to individual farmers. The reported take of at least 9,557 bi rds by Mississippi catfish Farmers had no apparent impacts on wintering pop ulations during 1998-99, Further monitoring of cormorant wintering populati ons over more of their wintering range is recommended.