Mink dive deep into the depths of New York’s Hudson River to hunt frogs and fish. Scurrying along the river shore, they nose around in the dirt, building dens.
But their food and shelter are giving them heavy doses of industrial chemicals, which could be killing their babies and jeopardizing their populations.
In a new study, farm-raised mink were fed fish caught in the upper Hudson River, which is highly contaminated with polychlorinated biphenyls (PCBs). Kits born to the parents that ate the compounds were much more likely to die than the kits of those that ate less-contaminated food.
“Based on the kit mortality, we believe PCB contamination is causing decreased abundance and density of mink in the upper Hudson River,” said Kathryn Jahn, a U.S. Fish and Wildlife Service biologist who worked closely with Michigan State University researchers on the study.
All of the kits from 15 mothers that ate no PCBs survived, along with 96 percent of those from the 10 mothers that ate the lowest amounts. But in the four groups fed increasing amounts of the chemicals, all 50 kits died – most within 10 weeks.
The region’s wild mink consume similar amounts of PCBs. As a result, it’s likely that large numbers are stillborn or dying young in the wild, too, the scientists said. “A diet comprised of less than 10 percent fish with these environmentally relevant PCB concentrations could be expected to result in kit mortality,” the study authors wrote.
For decades, scientists have known that mink are more sensitive than other animals to reproductive and immune damage from PCBs, but it remains a mystery as to why.
About two feet long with luxurious fur, mink are found throughout much of the United States and Canada in places with abundant marshes and other wetlands. Dependent on water for food, they dive into rivers and lakes to eat muskrats, chipmunks, fish, frogs and birds. They are trapped and farmed for their soft pelts.
Mink numbers appear stable, according to the New York Department of Environmental Conservation. However, trapping data suggest that the Hudson River populations are smaller than elsewhere in the state.
Since they’re near the top of the food chain – rarely falling victim to predators – mink accumulate large quantities of chemicals, said Niladri Basu, a University of Michigan professor who studies fish and wildlife as indicators of health hazards.
As a sentinel species, their health is indicative of the surrounding ecosystem’s health.
“At a regional or local level, these chemicals’ affect on populations should be a concern,” Basu said. “These isolated areas like the Hudson River and the South River in Virginia, where there used to be a Dow facility, show [mink] are really struggling with PCBs and mercury.”
The Hudson River is one of the largest, most contaminated Superfund sites in the country. From the 1940s to about 1976, two General Electric plants released an estimated 1.3 million pounds of PCBs into the 315-mile river. Now banned, the chemicals, which were used largely as insulators in large electrical equipment, have plagued the river since because they linger in the environment.
People have been warned for four decades to avoid eating most fish from the river. PCBs are linked to many human health effects, including cancer and reduced IQs in children from Great Lakes states.
As early as 1982, scientists began documenting elevated PCBs in mink along the river. Within three miles of the river, about half of them have levels in their liver above the threshold for health problems, according to a report from the National Oceanic and Atmospheric Administration.