Tiny Parasite Swallows Yellowstone
August 24, 2016
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Montana wildlife officials shut down almost 200 miles of the Yellowstone and its tributaries to recreation last week to prevent the parasite from spreading to other rivers, or south into Yellowstone National Park.
The white bodies of thousands of dead fish litter many parts of the river, victims of a parasite that causes a fatal illness called proliferative kidney disease, or P.K.D., in mountain whitefish. There have been reports that it is also killing trout, the prized game fish here. The outbreak has not spread to humans or other animals.
“The aroma of rotting fish tells you what we’re dealing with,” Travis Horton, a regional fisheries manager for Montana, said Tuesday as he inspected the riverbanks near here.
Outfitters along the river, used to doing a booming business in August, are shuttered. “We put 100 to 150 people a day on the river,” said Marlie Anderson, a partner at Rubber Ducky River Rentals on Livingston’s main street. Last week, however, “our business pretty much ground to a halt,” she said.
“Everybody’s kind of reeling,” said Roger Nelson, who, with his wife, Mary, owns Nelson’s Spring Creek, a half-mile stretch of prime trout stream that flows into the Yellowstone just south of town. Before the closing, he said, as many as 10 fishermen a day paid $120 each to fish on the Nelsons’ property and booked rooms in their lodge.
This parasite is not the first invasive species to disrupt life on the river. “We got through whirling disease and mud snails, and we’ll get through P.K.D.,” Mr. Nelson said.
The parasite is native to the northern US, Canada and Europe, but outbreaks have not been common. According to FWP, there have been only two isolated PKD outbreaks in Montana in the last 20 years.
Why such a huge outbreak, and why now?
According to the FWP release, the effect of the disease on Yellowstone’s fish populations is exacerbated by other stressors like near record low flows, consistent high temperatures, and the disturbance caused by recreational activities.
We know that these stressors are extreme:
The area of the Yellowstone River system that has suffered the PKD outbreak is suffering from extreme drought conditions. According to the Montana Department of Natural Resources and Water Conservation, Sweetgrass, Stillwater, and Yellowstone counties — the primary locations of the closure — are all suffering from extreme drought as of July, 2016.
PARADISE VALLEY — A previously unidentified strain of parasite has grown so prolific in the Yellowstone River that it is overwhelming whitefish, killing thousands and prompting the state last week to close more than 180 miles of the river to all recreation.
“The sheer parasite loading itself is almost shocking the fish, that’s what’s killing them,” said Eileen Ryce, Montana Fish, Wildlife and Parks’ hatchery section chief, during a Tuesday press conference along the banks of the Yellowstone River south of Livingston.
Scientists like Ryce believe that the parasite bloom may be so large and unprecedented in part because the Yellowstone River is experiencing near-record low flows and high water temperatures.
“We could see varying responses (of the parasite) depending on which river it gets into,” said Travis Horton, Region 3 fisheries manager in Bozeman.
The nearby Madison River, where flows are dam controlled, may be more resilient to the parasite since the water’s temperature is cooler, coming from the bottom of Hebgen Lake, and the flows can be maintained at a steadier rate. Likewise, outbreaks of similar parasites in Idaho that killed whitefish in 2011 and 2012 may have been more limited because some of the streams are dam controlled, Horton said.
We are examining how bryozoans act as a source of a disease in salmon and trout that is increasing in prevalence and severity as a result of environmental change.
Myxozoans are a group of parasites that live inside the bodies of their hosts. They have a complex life cycle, exploiting both vertebrate and invertebrate hosts. The myxozoanTetracapsuloides bryosalmonae develops in freshwater bryozoans and causes adevastating disease called Proliferative Kidney Disease (PKD) when transmitted to salmon and trout hosts.
PKD is emerging as a serious disease in wild and farmed fish populations as a result of environmental change.
We are investigating the drivers of PKD by:
- characterising bryozoan populations and the dynamics of the myxozoan parasite within this host
- establishing risk factors associated with disease prevalence, burden in bryozoans and disease transmission to fish