FWP: Parasite is causing unprecedented fish kill

By Joseph T. O’Connor and Amanda Eggert
EBS Staff

BOZEMAN – Montana Fish, Wildlife and Parks announced today the Yellowstone River and its tributaries are closed indefinitely to all recreation activities due to a parasite that has killed nearly 2,000 mountain whitefish and is starting to impact trout populations as well.

Fishing, floating, wading and tubing are prohibited from just north of the Yellowstone National Park boundary at the Gardiner entrance to Highway 212 bridge in Laurel. But in an Aug. 19 press conference at state FWP Region 3 Headquarters in Bozeman, FWP representatives took it a step further.

“Any entry into the river is prohibited,” said Andrea Jones, FWP’s region 3 information and education manager, at the press conference.

In total, 183 river miles are closed until environmental conditions improve and fish mortality ceases.

A National Park Service press release sent Friday afternoon stated that it will not extend the river closure into Yellowstone National Park, and that park crews have not seen any fish mortality related to the parasite, Tetracapsula bryosalmonae, which is known to cause proliferative kidney disease among affected fish.

The FWP-posted notice at the Pine Creek fishing access site on the Yellowstone River. PHOTO BY RYAN WEAVER

The FWP-posted notice at the Pine Creek fishing access site on the Yellowstone River. PHOTO BY RYAN WEAVER

Dr. Eileen Ryce, FWP’s hatchery bureau chief, said in the press conference that the parasite has been documented in other situations to cause upwards of a 90 percent mortality rate in salmonids. All trout and mountain whitefish are part of the salmonidae family, which also includes salmon, graylings and char.

High water temperatures and low flows have increased stress to fish and FWP representatives said the closure is intended to mitigate stressors to fish and decrease the likelihood that the parasite will spread to other waterways.

A study in the journal Aquaculture found that as water temperatures increase, proliferative kidney disease spreads more rapidly and increases fish mortality.

FWP fisheries biologist Dave Moser said rough calculations suggest up to 200,000 whitefish could have died from the disease—one of the most serious diseases to impact mountain whitefish and trout.

“This kill is unprecedented in its magnitude,” Jones said at the press conference. “We have not seen something like this in Montana.” Jones said this fish kill is remarkable for the duration of infection and the length of river impacted.

It appears the parasite was introduced to the river, although the exact mechanism is currently unknown. “Most likely [it was introduced] from other waters,” Moser said. “It could be boats that aren’t cleaned, drained and dried; it could be waders.”

Ryce said the fish were naïve to the parasite, meaning this would have been their first exposure to it. An Aug. 19 press release from FWP notes the parasite infection has been documented previously in two isolated locations in only Montana the past 20 years. Recent outbreaks have occurred in Washington, Oregon and Idaho. The parasite does not pose a risk to humans.

Moser said the infection has been worsening, as increasing numbers of fish succumb to the disease. Mountain whitefish, a salmonid species native to Montana, are bearing the brunt of the impact.

“We’re at a sort of peak of infection,” Moser said. “These fish are sort of rifled with this parasite, so it’s rampant throughout their bodies.”

Moser said small number of rainbow trout and Yellowstone cutthroat trout are believed to have died from the parasite as well.

One reason driving FWP’s decision to close the Yellowstone is the concern that recreational activities would cause mortalities in trout similar to what’s been documented in whitefish.

“It can, and will, and has killed Yellowstone cutthroat and rainbow trout,” said Sam Sheppard, FWP’s region 3 supervisor.

The economic impact to outfitting and guiding outfits along the Yellowstone, as well as other tourism-related businesses could be profound, Sheppard added. “Eyes wide open, this is going to be really tough on a lot of people … The overall recreation and fishing economic upside to this resource for decades past and decades to come is the most important thing.”

Jones noted the Yellowstone has been running exceptionally low and warm this summer. She said the Yellowstone is running just 300 cubic feet per second higher than it’s historic, all-time low.

“To my knowledge, [in] southwest Montana, we haven’t had a closure to this extent on a river … and to my knowledge, we’ve never closed all water-based recreation,” said Travis Horton, FWP’s region 3 fisheries manager, at the press conference.

Dead whitefish and a rainbow trout in the Yellowstone River on Aug. 19 just below the Emigrant bridge. PHOTO BY DAVID ALLEN

Dead whitefish and a rainbow trout in the Yellowstone River on Aug. 19 just below the Emigrant bridge. PHOTO BY DAVID ALLEN


“Clean, drain, dry” is FWP’s recommendation for limiting the spread of aquatic invasive species. Gear—including boats, waders and trailers—should be washed with warm water, using a pressure washer if possible. Drain gear and let it dry completely before storage or use in other waterways.

“This is going to hinge on public cooperation—everybody taking the clean, drain, dry message and utilizing and doing that,” Sheppard said.

Two aquatic invasive species decontamination stations have been set up along I-90 just west of Livingston and just east of Big Timber.

FWP is posting closure notices along fishing access sites that will be closed, and is imploring the public to limit the spread of the parasite by properly cleaning all equipment prior to moving between water bodies.

“This is a crisis moment,” Sheppard said. “You can’t throw a stick for your dog [into the Yellowstone River]. That’s how serious this is.”

FWP representatives said they the closure will remain in place until stream conditions such as flow and temperature improve and fish mortality ceases.

EBS will continue following this developing story and post updates as information becomes available.