MEASURES OF REPRODUCTIVE SUCCESS AND POLYCHLORINATED BIPHENYL RESIDUES IN EGGS AND CHICKS OF FORSTER TERNS ON GREEN BAY, LAKE-MICHIGAN, WISCONSIN - 1988

Data on reproductive success of Forster's tern (Sterna forsteri) from Green Bay, Lake Michigan in 1983 are compared with data collected in 1 988. In 1988 measures of reproductive performance (hatching success, n umber of young fledged, and length of incubation) were improved. Conce ntrations of total polychlorinated biphenyls (PCBs) and planar PCB con geners in the eggs were compared between years. Median total PCB resid ue was 67% lower in 1988 (XBAR = 7.3 mug/g). This corresponds to a 42% reduction in tetrachlorodibenzo-p-dioxin equivalents (TCDD-EQ) from 1 983 to 1988. We suggest that contaminant reduction and improved reprod uctive performance were due to low river flows in 1988 and associated reduced PBC loading into Green Bay. Forty-two percent of the matured c hicks died before fledgling, and their body weight growth curves were much lower than normal. Young accumulate total PCBs at a rate of 17.6 mug/day. A no-observable-adverse-effects level (NOAEL) of 40-84 mug/kg /day was estimated from the two year results using the least observabl e adverse effects level (LOAEL)/NOAEL rating values.