A field trial is described in which sudan black, a known embryocide, was inserted into fish used as bait for herring gulls on Muskeget Island, Massachusetts, in order to reduce reproductive success. Two baiting strategies were compared: remote (at major garbage dumps on Cape Cod), and proximate (over the eastern half of the island). Both treatments showed effectiveness in reducing reproductive success. The economics of conducting such a treatment to sterilize virtually the entire herring gull population in New England are discussed.