CONCENTRATIONS OF MERCURY AND SELENIUM IN TISSUES OF DOUBLE-CRESTED CORMORANTS (PHALACROCORAX-AURITUS) FROM SOUTHERN FLORIDA

Tissues from 99 Double-crested Cormorants (Phalacrocorax auritus) coll ected between 1994 and 1997 from southern Florida, were analyzed for c oncentrations of mercury and selenium. These concentrations were corre lated with each other, including concentrations of mercury and seleniu m in liver. Mercury and selenium in liver increased from a mean of 15 and 8 mg kg(-1) wet weight (ww) in the fall, winter and spring to a me an of 41 and 13 mg kg(-1) ww in the summer, respectively. Similarly, c oncentrations of mercury in brain increased from a mean of 1.3 mg kg(- 1) ww in the fall, winter and spring to a mean of 2.2 mg kg(-1) ww in the summer. Concentrations of selenium in liver increased with age. Se x, physical condition, year, and geographic location of recovery had n o significant effect on mercury and selenium concentrations. Between 1 2 and 15% of the cormorants studied had hepatic selenium and mercury c oncentrations of over 20 and 50 mg kg(-1) ww, respectively (considered lethal in some avian species). Liver selenium concentrations of over 3 mg kg(-1) ww and brain mercury concentrations above 2 mg kg(-1) ww ( related to reproductive failure in adult loons and mallards) were obse rved in 57% and 32% of the cormorants studied, respectively These resu lts could mean that Double-crested Cormorants in southern Florida migh t be at risk of mercury and selenium poisoning.