Monitoring and assessment of population, reproductive, and health effects in colonial waterbirds breeding at contaminated Great Lakes sites in Michigan

Immunological, reproductive, and population endpoints were assessed in fish-eating birds during 2010–2019 in the Saginaw River and Bay and River Raisin Areas of Concern (AOCs) and Grand Traverse Bay, which are ecosystems historically contaminated with polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans. Reference sites were in the lower St. Marys River (herring gulls and Caspian terns), eastern Lake Superior (terns), and eastern Lake Huron (black-crowned night herons). Relative risk ratios for embryonic nonviability (from both infertility and mortality) in gull embryos were 2–3-fold higher than the reference site in both AOCs and Grand Traverse Bay. Twelve of 13 deformed embryos and chicks (e.g., crossed bills and gastroschisis) were observed at the contaminated sites. Productivity of 4-week-old tern chicks in Saginaw Bay was 35% lower than that at reference sites. In the River Raisin AOC, productivity of 4-week gull chicks was poor in 7 of 10 years. Numbers of breeding herring gulls decreased significantly in the River Raisin AOC, and breeding Caspian terns, a state-threatened species, declined in the Saginaw River and Bay AOC. The mean T cell-dependent phytohemagglutinin skin response was suppressed 50%–56% in gull chicks in both AOCs and Grand Traverse Bay, and 49% in terns and 33% in herons in Saginaw Bay. Antibody responses in gull chicks in the River Raisin AOC and Grand Traverse Bay were 1.6–2-fold lower than reference. Time trend analyses showed no significant improvements in reproductive and immune endpoints in either AOC or Grand Traverse Bay over the study period. Embryonic death increased with time in gulls in the lower Saginaw Bay, and antibody responses decreased in terns in the outer Saginaw Bay.