Fish death toll climbs on Yellowstone River

August 25, 2017 GMT

Nineteen more dead mountain whitefish were found by Montana Fish, Wildlife and Park staff as they floated the Yellowstone River in the Paradise Valley on Thursday.

The crew captured one fish close to death, which will help scientists more easily determine the cause of mortality.

Thursday’s monitoring floats followed similar efforts Monday and Tuesday on the Yellowstone River between Livingston and Springdale. Those floats turned up 76 dead whitefish, two dead suckers and one dead brown trout.

Official test results won’t be available until next week at the earliest, and biologists don’t have enough information yet to determine the cause of the localized and limited fish kills.

“We’re still collecting information at this point,” said Travis Horton, Region 3 fisheries manager, in a press release. “We aren’t currently considering any closures or restrictions. However, we ask that anglers not target mountain whitefish.”

On Friday, FWP crews are planning to search the river between Livingston and Springdale where they’ve found the bulk of the dead fish.

Thursday’s monitoring float focused on the Yellowstone from Grey Owl fishing access site to Pine Creek. That section of the river was the hardest hit during last summer’s outbreak of proliferative kidney disease, or PKD. In 2016, upwards of 1,900 dead mountain whitefish were found on one bank of the river.

PKD is caused by a microscopic parasite that exists in the river year-round. Though the reason the parasite will suddenly cause PKD is unknown, high water temperatures, low flows and fish stress can be factors.

Last summer the PKD outbreak on the upper Yellowstone River led to an emergency closure of a large section of the river by FWP and the death of thousands of mountain whitefish, which are native to the river. Historically low flows in the river coupled with high water temperatures last summer helped to exacerbate the impacts of PKD on whitefish.

Conditions this year are much different — water temperatures have remained cooler and flows are above average. In addition, the time of year is later with longer, cooler nights. These environmental differences could result in a much different scenario and outcome compared to last year’s fish kill.