Chlorinated hydrocarbon contaminants and productivity of bald eagle populations on the Pacific coast of Canada

From 1991 to 1995, we studied bald eagle populations breeding near three pulp mills in the Strait of Georgia, in the Fraser River estuary, and at remote reference sites on the west coast of Vancouver Island, northern Johnstone Strait, and the Queen Charlotte Islands (Haida Gwaii). Our objective was to determine occupancy of breeding territories, measure nest success, and compare the results to chlorinated hydrocarbon levels in eggs and in nestling plasma samples. Blood samples were collected in 1993 and 1994 from 52 nestlings in 38 nests and plasma analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), organochlorine (OC), pesticides, and lipid content. Most measured compounds partitioned with plasma lipids, with the exception of hepta- and octachlorinated dioxins and furans. Because of significant variation in plasma lipid content among sites, contaminant concentrations were adjusted using analysis of covariance (ANCOVA). Mean concentrations of 2,3,7,8-substituted PCDDs, PCDFs, and calculated international toxic equivalents (I-TEQs) in nestling plasma were highest in samples from near pulp mills on southeast Vancouver Island (Nanaimo and Crofton) and Powell River. Mean total PCB concentrations were also highest in the industrialized Strait of Georgia region, such as at Powell River (56 micrograms/kg), while OC pesticide concentrations, including 1,1-dichloroethylene bis(p-chlorophenyl) (DDE), did not vary significantly among sites. Nest success was followed for 5 years at 250 breeding territories in the nine study areas. Average productivity was higher at most study sites around the Strait of Georgia compared to the reference areas. There were no significant relationships between productivity and I-TEQs or any tetrachlorodibenzo-p-dioxin-like compounds for the whole data set; only DDE in plasma was weakly related to productivity. Likewise, there were no significant relationships between individual nest productivity and contaminant levels in eggs, based on previously published data. We also tested for variability within study areas by comparing productivity at nests adjacent to dioxin fishery closure areas at three pulp mills compared to nearby nests outside the closure areas. At two pulp mill sites, Powell River and Nanaimo, there were no differences in productivity; however, at Crofton, average productivity, 0.26 young/occupied territory, was significantly lower at nine bald eagle territories adjacent to a dioxin-fishery closure zone compared to eight territories outside of the closure area, 1.0 young/occupied territory. The cause of the low reproductive rate at Crofton has not been determined, although a toxicological explanation has not been ruled out.