Human Health: Other issues -- Wildlife populations

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Other issues in the Great Lakes

Other health issues
in the Great Lakes
Apart from the major Great Lakes health concerns of drinking water, recreational water, and fish consumption, there are a number of related issues that are interconnected to air and water quality, pollution and contamination, agriculture and industry, and wildlife.

Wildlife populations
The health of fish and wildlife provides a good indication of the overall condition of an ecosystem. Research over the last 25 years has shown that a variety of persistent, bioaccumulative contaminants in the Great Lakes food chain are toxic to wildlife. There is a growing body of literature supporting the use of wildlife populations as indicators of ecosystem health; it suggests that many species are sentinels for toxic chemical effects, although conclusive linkages between all such effects and chemicals remain elusive.

Reproductive impairments have been described in the populations of birds, fish, and mammals. For example, egg loss due to eggshell thinning has been observed in predatory birds, such as the bald eagle. After feeding on Great Lakes fish for two or more years, immigrant birds were shown to have a decline in reproductive success. Developmental effects in the form of congenital deformities (crossed mandibles, club feet) have also been reported in bird populations within the Great Lakes basin.

Effects on the immune system, in particular, have been a notable finding. At a number of great Lakes sites, a survey of herring gulls and Caspian terns demonstrated a suppression of T-cell-mediated immunity following prenatal exposure to organochlorine pollutants, particularly PCBs.

Not all wildlife in the basin are beneficial, either because a species is non-native/invasive or because a species is locally too abundant. For example, gulls and geese are sources of biological pathogens that can cause problems in local areas if the birds are overly abundant.

Top native predators, however, such as the bald eagle and osprey, are gradually making a comeback in the watershed after years of decline due to reproductive failure caused by toxic chemicals. As levels of contaminants dropped in the food web, contaminant concentrations in these top predators, along with the associated health effects, also decreased. However, there are still continuing problems with wildlife in the Great Lakes basin.

Ongoing fish and wildlife populations can provide an important tool to identify any currently unrecognized contaminant risks that may develop in the future. Given that the metabolisms and diets of wildlife are very different from humans and that these species are exposed to much higher contaminant levels than the general human population, caution must be used when interpreting the significance of fish and wildlife problems for human populations.

Nevertheless, both Canadian and U.S. health agencies have concluded that the weight of evidence based on the findings of wildlife biologists, toxicologists, and epidemiologists clearly indicates that populations continue to be exposed to PCBs and other chemical contaminants and that significant health consequences are associated with these exposures.

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Photos: Great Lakes National Program Office of the U.S. EPA
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