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Massive Montana Fish Kill

(Enterprise photo by Hunter D'Antuono)

Alarming news from the American West this week — reported by Reuters and the Associated Press, a 186 mile stretch of the Yellowstone River in Montana and it's tributaries have been closed by officials after a massive fish-kill that is being attributed to an aquatic parasite.  Over 4,000 Mountain Whitefish and a smaller, undetermined number of trout have been found dead.

As quoted from the Livingston Enterprise, "Test results from samples sent to the U.S. and Wildlife Service Fish Health Center in Bozeman show the catalyst for this fish kill to be Proliferative Kidney Disease — one of the most serious diseases to impact whitefish and trout. The disease, caused by a microscopic parasite, is known to occur in Canada, the U.S. and Europe. It has been documented previously in only two isolated locations in Montana over the past 20 years. Recent outbreaks have occurred in Washington, Oregon and Idaho. In trout, research has shown this disease to have the potential to cause 20 to 100 percent mortality. The parasite does not pose a risk to humans."

"The Montana Department of Fish, Wildlife and Parks (FWP) is implementing an immediate closure of all water-based recreation (fishing, wading, floating, tubing, boating, etc.) on the Yellowstone River and its tributaries from Yellowstone National Park's northern boundary at Gardiner to the Highway 212 bridge in Laurel, according to an FWP news release."


Tetracapsuloides bryosalmonae — the organism that causes Proliferative Kidney Disease in Whitefish and trout — is a myxozoan parasite of salmonid fishes.


The intention of the restriction on activities is intended to curb the potential spread of the organisms on contaminated items.

In the 1990's in Colorado, another related piscine disorder — Whirling Disease — was spread throughout waterways via myxosporean parasites that attached themselves to felt soled wading boots used by traveling fishermen.

Toxic chemical spills are generally thought to be the more common cause of large fish mortality events, but pathogenic organisms are capable of moving through aquatic environments with surprising speed as well. The outbreak has not escaped the attention of state regulatory agencies.

"This kill is unprecedented in magnitude. We haven't seen something like this in Montana," Fish, Wildlife and Parks spokeswoman Andrea Jones said in Associated Press coverage of the issue.


While biologists are monitoring the environmental impacts, elected officials are weighing the potential economic ones — and the costs of a lack of response. AP coverage again reports,

"A threat to the health of Montana's fish populations is a threat to Montana's entire outdoor economy and the tens of thousands of jobs it sustains," said Gov. Steve Bullock, noting that Montana's outdoor recreation economy is responsible for more than 64,000 Montana jobs and nearly $6 billion in yearly economic activity. "We must be guided by science. Our state cannot afford this infectious disease to spread to other streams and rivers and it's my responsibility to do everything we can to stop this threat in its tracks and protect Montana jobs and livelihoods."

The closure could potentially last for the remainder of the season if river water temperatures don't cool, which would reduce stress on fish populations. Currently extending to hundreds of miles of waterways that feed into the Yellowstone, including the Boulder, Shields and Stillwater rivers, FWP will continue to monitor the river and will lift the closure when stream conditions improve and fish mortality ceases.


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