Food habits and organochlorine contaminants in the diet of olivaceous cormorants in Galveston Bay, Texas

More than 1,000 food items, representing 32 species of fish and one invertebrate, were identified from olivaceous cormorants. Six species of fish comprised 79% of the diet by frequency of occurrence and 78% by weight. Almost half of the diet consisted of a single species, the sheepshead minnow. Concentrations of pp-dichlorodiphenyldichloroethylene (DDE) in cormorant carcasses were 27 times greater than those in fish and 57 times higher in cormorant eggs than fish. Concentrations of polychlorinated biphenyl (PCB) were 18 times higher in carcasses and 15 times higher in eggs than in fish. The biomagnification of other organochlorine contaminants through the cormorant food base in Galveston Bay is difficult to evaluate because the only compounds detected in all three tissues at greater than 50% frequency of occurrence were DDE and PCB.