Summary

Description

Numbers of bald eagles Haliaeetus leucocephalus nesting along the lower Columbia River have doubled in the last six years, yet fiveyear running productivity averages are well below statewide values for eagles nesting in other areas of Oregon and Washington. While productivity of eagles along the Columbia River is low, nesting success in other areas of the two states is close to the goals established to delist the species from the Federal Endangered Species list. Previous contaminant studies conducted from 1985 to 1987 along the river found poor productivity associated with elevated DDE dichlorodiphenyldichloroethane and total polychlorinated biphenyls PCBs in eagle eggs. In addition, 2,3,7,8tetrachlorodibenzopdioxin TCDD and 2,3,7,8tetrachlorodibenzofuran TCDF concentrations were found in five eggs collected in 1987 and 1991. From 199495, fresh bald eagle eggs were collected from nests in 19 of 43 occupied territories along the river. Eggshell thickness was determined on all eggs, and the contents were analyzed for organochlorine pesticides, total PCBs, polychlorinated dibenzopdioxins PCDDs, polychlorinated dibenzofurans PCDFs, and planar PCBs nonortho and monoortho substituted congeners. Halogenated dioxinlike compounds in eggs were also evaluated based on a H4IIE rat hepatoma bioassay. Productivity and egg contaminant results from l 994 to 1995 were compared to a previous study to evaluate changes over time. Recent increases in productivity averages were due to new pairs nesting along the river, yet productivity at 23 older breeding areas remained low and was not different P0.713 between the two study periods. Eggshells averaged 11 percent thinner than shells measured prior to the use of the pesticide DDT dichlorodiphenyltrichloroethane, and thickness of eggs from older breeding territories had not improved P0.404 between the two study periods. Decreases in p,pDDE P0.022 and total PCBs P 0.0004 in eggs from older breeding areas occurred between the two study periods, but concentrations were still above values associated with poor productivity. TCDD toxic equivalents TEQs exceeded estimated noeffect values for bald eagles during both studies. Bald eagle productivity over a fiveyear time period encompassing egg collection was not correlated to individual organochlorine compounds. Some dioxins, furans, planar PCBs, and TEQ values were correlated to nest location as river mile, with highest concentrations occurring at downriver breeding territories near the mouth. Although total productivity has increased due to the success of new nesting pairs moving into the region, results indicate that organochlorine contaminants continue to impact the breeding success of lower Columbia River eagles. The greatest impact of appears to occur at older breeding territories, which were located predominantly in the lower estuary below river mile 60. Eagles nesting toward the mouth of the river may be at greater risk of exposure to some dioxinlike compounds, and the reproductive success of some new pairs nesting in this area could be impacted in the future.