EVALUATION OF THE EFFECTS OF TOXIC-CHEMICALS IN GREAT-LAKES CORMORANTS - HAS CAUSALITY BEEN ESTABLISHED

Toxic contaminants have influenced Double-crested Cormorant (Phalacroc orax auritus) reproduction on the Great Lakes for at least three decad es. Four recent studies of contaminants in cormorants of the Great Lak es region are reviewed for their conformation with epidemiological cri teria used to infer cause and effect linkages (CELs). Growth of the po pulation was interrupted by DDT which led to egg-shell thinning and re duced reproduction which hid other developmental problems that were mo st likely caused by planar PCB, dioxin and furan contaminants. Three s tudies investigated embryo viability and deformities in the post-DDT e ra. A study of the effects of planar contaminants measured by the H4II E bioassay technique on egg viability was judged to be strong demonstr ation of contaminant effects on the cormorant population. Two studies of bill defects and the co-occurrence of embryonic abnormalities with specific toxic PCB and dioxin congeners as cormorant teratogens were f ound to have weaknesses, but were consistent with the paradigm that pl anar chlorinated hydrocarbons (PHHs), especially the non-ortho-substit uted PCB congeners, are now the most important toxic chemical problem for cormorants in the Great Lakes. The rapid uptake of PHHs and great interspecific variations of sensitivity to effects of these chemical b etween Larids and cormorants have been observed. These biochemical dif ferences and high cormorant fecundity help account for the rapid recov ery of cormorants on the Great Lakes. PHHs have relatively trivial imp acts on cormorant populations, but do cause significant damage to indi viduals in a dose-dependant manner. Congener-specific and bioassay tec hniques support the development of a new toxic chemical paradigm with large implications to policy, management and water quality criteria us ed to make regulatory decisions. Cormorants may have actually benefite d from exposure to toxic contaminants in their competition with large gulls (Larus spp.) on the Great Lakes in the post-DDT era.