Organochlorine contaminants and reproductive success of double-crested cormorants from Green Bay, Wisconsin, USA

In 1994 and 1995, nesting success of double-crested cormorants (Phalacrocor ax auritus) was measured at Cat Island, in southern Green Bay, Lake Michiga n, Wisconsin, USA. Sample eggs at pipping and unhatched eggs were collected and analyzed for organochlorines (including total polychlorinated biphenyl s [PCBs] and DDE), hepatic microsomal ethoxyresorufin-O-dealkylase (EROD) a ctivity in embryos, and eggshell thickness. Of 1,570 eggs laid, 32% did not hatch and 0.4% had deformed embryos. Of 632 chicks monitored from hatching to 12 d of age, 9% were missing or found dead; no deformities were observe d. The PCB concentrations in sample eggs from clutches with deformed embryo s (mean = 10.2 mu g/g wet weight) and dead embryos (11.4 mu g/g) were not s ignificantly higher than concentrations in sample eggs from nests where all eggs hatched (12.1 mu g/g). A logistic regression of hatching success vers us DDE, dieldrin, and PCB concentrations in sibling eggs identified DDE and nor dieldrin or PCBs as a significant risk factor. A logistic regression o f hatching success versus DDE and eggshell thickness implicated DDE and nor eggshell thickness as a significant risk factor. Even though the insectici de DDT was banned in the early 1970s, we suggest that DDE concentrations in double-crested cormorant eggs in Green Bay are still having an effect on r eproduction in this species.