Wildlife Rangers Think They Finally Discovered Why Dozens of Whitefish Were Found Dead on Yellowstone River

by Lauren Boisvert

Over Labor Day weekend, dozens of whitefish washed up dead on the shores of the Yellowstone River in Montana. According to KPVI, fishermen first noticed the dead fish in the river over the Sept. 8 weekend, and later Montana Fish, Wildlife, and Parks officials checked out the situation. They searched between the Grey Owl and Mallard’s Rest fishing sites in Paradise Valley and found 57 dead mountain whitefish.

FWP collected several of the dead fish for testing and study; they found that proliferative kidney disease, or PKD, likely killed the fish; PKD is one of the most devastating diseases for salmonids, as “outbreaks cause severe economic constraints for the aquaculture industry and declines of wild species,” according to a 2020 study of the disease. The myxozoan parasite Tetracapsuloides bryosalmonae causes the disease.

PKD has affected the Yellowstone River in the past; in 2016 there was a significant outbreak that resulted in FWP closing 183 miles of the river. The  Bozeman Fish Health Center identified PKD as the cause of death by looking for anemia and severe kidney inflammation. According to the National Park Service, “clinical signs [of PKD] usually only develop when water temperatures exceed 59 degrees F for several weeks or longer.”

According to KPVI, there are currently no closures or restrictions on the Yellowstone River or its tributaries.

How Disease Affects Yellowstone and Other National Parks

In 2015, the USGS put together a compilation of its most important animal disease studies in the National Parks. They studied mange in wolves, finding that mange plagued 2 of 8 Yellowstone wolf packs. Mange, a highly contagious skin disease caused by mites, presents as hair loss, skin infections, irritation, and scratching. This can result in hypothermia, malnutrition, dehydration, and death.

The USGS also studied the plague in Wind Cave National Park. Affecting the black-footed ferret, one of the most endangered mammals in North America, the sylvatic plague is caused by fleas and can also affect humans. The plague also heavily affects prairie dogs, which are already declining due to habitat loss and poisoning. An entire local prairie dog population can go extinct from the plague, as they “suffer high mortality rates of 90 percent or more during plague outbreaks,” according to the USGS. But researchers can vaccinate ferrets and prairie dogs against the plague; the USGS National Wildlife Health Center created vaccines that look like food to easily vaccinate the free-roaming populations.

In fish, scientists tend to sample from the water as a non-invasive alternative to sampling fish tissue. But, according to the National Park Service, “detecting parasite DNA in water does not imply the presence of a viable parasite population or indicate widespread infection in fish at that location.” Sampling the water is good for detecting parasite “hotspots” along the rivers, and indicating which fish species should be collected for study.

Widespread diseases in the National Parks can lead to severe population depletion; they can also curb the populations in ways that mimic natural selection, weeding out the weak animals from the herds or packs that would’ve died from more natural causes. Still, diseases in the National Parks should be extensively studied and prevented if possible.