The biological pathway and effect of PCBs on common terns in Lake Michigan.

Poly-chlorinated biphenyls (PCBs) have been recognized as a significant contaminant in the Great Lakes ecosystem. Although PCBs are implicated in the reduced survival and reproductive success of several piscivorous bird species, the biological pathway in which PCBs bioaccumulate remains largely unknown. This study investigates the two most likely biological pathways, suggested via research on Great Lakes sport fish, by which PCBs would be acquired by common terns (Sterna hirundo), a piscivorous species of conservation concern. The first proposed pathway is through atmospheric deposition of PCBs which are subsequently acquired by filter-feeding fish (e.g., alewives, Alosa pseudoharengus). An alternative pathway is via the biodeposits of zebra mussels which are consumed by shallow water fish (e.g., round gobies, Neogobius melanostromus). Because common terns breed in near-shore sites where concentrations of zebra mussels are found, as well as forage in more pelagic environments it is possible that either or both pathways may be contributing to their PCB exposure. Field experiments and stable isotope analyses suggest the most likely pathway by which terns are exposed to PCBs is via alewives, similar to how apex predators such as lake trout acquire PCBs. Biodeposits from zebra mussels do not appear to be a significant factor in PCB accumulation in terns. We quantified extremely poor parental attentiveness during incubation. Although we cannot determine whether poor parental attentiveness alone or in combination with PCB contamination led to low hatching success, accumulation of PCBs appears to have significant impacts on the overall reproductive success of common terns.