Thousands of whitefish die on South Fork
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Thousands of mountain whitefish have perished along the South Fork of the Snake River since last Thursday, the Idaho Department of Fish and Game said.
It is suspected the deaths have been caused by a parasite that causes a kidney disease that affects salmonids. In 2012, hundreds of whitefish died, but this year is the worst that Fish and Game workers have seen.
The culprit of the die-off appears to be the tetracapsuloides bryosalmonae, a myxozoan parasite that causes the proliferative kidney disease, or PKD.
“Last Thursday and Friday we electro-shocked the area looking for fish that appeared to be sick,” said Brett High, a regional fisheries biologist. “We found about one out of every 75 whitefish captured appeared to be sick, leaving a lot of healthy fish.”
Even though testing has shown that some trout contain the parasite, no trout has been found to have been killed by it. In some European countries trout have died from PKD, but Idaho has not seen any PKD-related deaths.
“It appears that the development of PKD may be heat related,” said Dan Garren, the regional fisheries manager. “The rising water temperatures during midsummer causes stress in the fish, which makes them susceptible to many diseases, which may include PKD.”
Garren said that a fresh water sponge appears to be the host for the parasite and as the sponge spores enter the water, the parasites enter the fish and attack their kidneys.
“We have seen a few fish die each year since 2012 of PKD,” said High. “But this year it is the heaviest, especially from the Palisades Dam to Conant Valley.”
It will be several weeks before the pathologists are positive that PKD is the killer, but it is suspected as Montana has seen it and because of its history on the South Fork.
Idaho has not placed any restrictions on activities on the South Fork of the Snake River.