Contaminants and Double-Crested Cormorants

Double-crested Cormorants and Contaminants in the Columbia River Estuary

Concentrations of DDE (a breakdown product of the pesticide DDT), total PCBs, mercury, and some dioxin-like compounds measuredPhoto - Double-crested cormorant eggs and hatchlings (USFWS).as toxic equivalents (TEQs) have accumulated in eggs of double-crested cormorants from colonies on Rice and East Sand Islands in the Columbia River Estuary, whereas samples from a reference colony were significantly lower or below detection limits. Nearly all contaminant concentrations in Rice Island cormorant eggs were higher than concentrations in eggs from cormorants at East Sand Island. Concentrations of these contaminants, particularly in eggs from the Rice Island colony, approached or exceeded some effect threshold levels during some years of the study, indicating some developing chicks may be harmed by contaminants.

Eggs from both colonies exhibited eggshell thinning, and eggshell thickness was inversely correlated to DDE concentrations. Eggs collected in 1991 from both islands exhibited mercury concentrations within a range associated with reproductive impacts for some avian species. Maximum concentrations of dioxin (TCDD) or TEQs in eggs from Rice Island also exceeded concentrations associated with reproductive impacts in birds from the Great Lakes and concentrations affecting brain asymmetry measurements. PCB 126 was found to contribute the most dioxin-like toxicity toward the mean TEQ concentrations in all additive models, which Photo - Double-crested cormorant chicks, lower Columbia River (USFWS).coincides with studies of other piscivorus birds along the lower Columbia River. Results indicate that lower Columbia River cormorants, especially birds nesting on Rice Island, are exposed to concentrations of contaminants that decrease shell thickness, adversely impact developing embryos, or result in egg mortality in some individuals. However, contaminant concentrations since 1994 appear to be well below concentrations impacting double-crested cormorants at the population level, in contrast to other field studies from the Great Lakes region.

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