SPATIAL AND TEMPORAL TRENDS IN ORGANOCHLORINE CONTAMINATION AND BILL DEFORMITIES IN DOUBLE-CRESTED CORMORANTS (PHALACROCORAX-AURITUS) FROM THE CANADIAN GREAT-LAKES

The levels of organochlorine contaminants (OCs) in the eggs of double- crested cormorants (Phalacrocorax auritus) from the Canadian Great Lak es, Lake Nipigon and Lake-of-the-Woods were monitored between 1970 and 1995. PCBs and p,p'-DDE were present at the highest concentrations. S ignificant declines in OC concentrations on the Great Lakes were obser ved over this period for Lake Ontario, Lake Superior, Georgian Bay and North Channel but not Lake Erie where levels remained relatively stab le. In the early 1970s, the greatest OC levels were generally observed in cormorant eggs from nesting sites in Georgian Bay and North Channe l of Lake Huron. Between 1984 and 1995 mirex and PCB levels were consi stently highest in samples from Lakes Ontario and Erie, respectively. Similar levels of PCDDs and PCDFs were observed from all regions of th e Canadian Great Lakes in 1989. In general, OC levels in cormorant egg s between 1984-95 were ranked as follows: Lake Erie>Lake Ontarior grea ter than or equal to Lake Superior>Lake Huron. In 1995, eggshell thick ness in Canadian Great Lakes cormorants, ranged from 0.423 to 0.440 mm and was on average only 2.3% thinner than pre-DDT era values. Between 1988 and 1996, 31 cormorant chicks with bill defects were observed at 16 different colonies (21% of all colonies surveyed) in Lakes Ontario and Superior, Georgian Bay and North Channel, and the main body of La ke Huron. No bill deformities were observed at reference sites in nort hwestern Ontario (Lake Nipigon and Lake-of-the-Woods). For the period 1988-96, the prevalence of bill defects in cormorant chicks (0.0 to 2. 8/10,000 chicks) did not differ significantly (P > 0.05) among most re gions in the Canadian Great Lakes. Georgian Bay was the only region to show a significant decrease in the prevalence of bill defects between the periods 1979-87 and 1988-95.