Organochlorine Residues and Shell Thinning in Oregon Seabird Eggs

Abstract

A single egg was collected at 62 nests of 10 seabird species from Oregon in 1979. The eggs were analyzed for organochlorine contaminants; con- temporary shell thickness was compared with eggshells collected during earlier time periods. Concentrations of DDE and PCB's in 1979 were generally low with the most contaminated species being the Double-crested Cormorant (Pha- lacrocorax auritus), Leach's Storm Petrel (Oceanodroma leucorhoa), and Fork- tailed Storm Petrel (0. furcata). Limited eggshell data provide evidence that shell thinning was more severe along the Oregon coast in the 1950's than in 1979. With the possible exception of the Fork-tailed Storm Petrel, the residues in 1979 posed no known threat to the welfare of the species. Seabirds have received increased attention during the last decade, partially because of the increase in man's activities in the coastal zones, but also because of the exposure of sea- birds to environmental pollutants in many locations (Ohlendorf et al. 1978). Pollutants in Oregon seabirds have not been systematically studied; however, an evaluation of a Common Murre (Uria aalge) die-off in 1969 included an analysis of dead birds for organochlorine pesticides and polychlorinated biphenyls (PCBs) (Scott et al. 1975). DDE and PCB residues in the murres were considerably below reported lethal concen- trations in other species of birds. Oregon's breeding seabird population is relatively large and diverse. Varoujean (1979) listed 46 colony sites in Oregon and about 1.2 million breeding seabirds of 13 species. The present study was undertaken to determine organochlorine burdens in seabird eggs collected along the Oregon coast, to evaluate the importance of the resi- dues detected, and to compare the residues with those reported from the same species in other localities.