CONTAMINANTS IN FISHES FROM GREAT LAKES-INFLUENCED SECTIONS AND ABOVEDAMS OF 3 MICHIGAN RIVERS .3. IMPLICATIONS FOR HEALTH OF BALD EAGLES

Recently, there have been discussions of the relative merits of passag e of fishes around hydroelectric dams on three rivers (Au Sable, Manis tee, and Muskegon) in Michigan. A hazard assessment was conducted to d etermine the potential for adverse effects on bald eagles that could c onsume such fishes from above and below dams on the three primary rive rs. The hazard assessments were verified by comparing the reproductive productivities of eagles nesting in areas where they ate vl primarily fish from either above or below darns on the three primary rivers, as well as on two additional rivers in Michigan, the Menominee and Thund er Bay. Concentrations of organochlorine insecticides (OCI), polychlor inated biphenyls (total PCBs), 2,3,7,8-tetrachlorodibenzo-p-dioxin equ ivalents (TCDD-EQ), and total mercury (Hg) were measured in composite samples of fishes from above and below hydroelectric darns on the Mani stee and Muskegon Rivers, which flow into Lake Michigan, and the Au Sa ble River, which flows into Lake Huron. Mean concentrations of OCI, to tal PCBs, and TCDD-EQ were all greater in fishes from below the dams t han in those from above. The hazard assessment indicated that current concentrations of Hg and OCI other than DDT (DDT + DDE + DDD) in fish from neither above nor below dams would present a significant hazard t o bald eagles (Haliaeetus leucocephalus). Both total PCBs and TCDD-EQ in fishes from below the darns currently present a significant hazard to bald eagles, since their mean hazard quotients (HQ) were all greate r than one.