Idaho Fish and Game is blaming a slight dip in the overall trout population on low flows from last winter on after conducting its annual fall fish survey of the South Fork of the Snake River.

Fisheries biologists say anticipated low flows this coming winter could also cause more reductions in overall fish population by next year. The recent surveys in the Conant reach and Lorenzo reach of the South Fork found a decrease from 6,175 trout per mile to 4,617 trout per mile and 2,650 trout per mile to 2,359 trout per mile respectively.

“That’s always going to be our biggest concern because mortality of all trout species is highest over the winter in the South Fork,” said Pat Kennedy, Fish and Game fisheries biologist. “We’re looking at limited flows. We can anticipate that abundances will be lower next year. I’m not for sure how much.”

On Wednesday, river flows from Palisades Dam were below 900 cubic feet per second, which is similar to the minimum flows during last winter.

Kennedy said previous winters pushed the South Fork’s fish populations above average, but now the numbers are trending downward.

“Last year we had a little bit of a decline and this next year if we continue to have declines, then I think we’ll start to be concerned about how that affects fishing and cutthroat populations,” he said.

The fall trout population surveys are sponsored by the Bureau of Reclamation as part of an effort to monitor the effects of winter flows from Palisades Dam.

Despite a population that’s trending downward, Kennedy said the population is just under the 10-year average and remains one of the most popular fisheries in eastern Idaho.

“There’s a lot of fish in the river still,” he said. “We’re a little down from our record abundances two years ago, but every year can’t be a record. I think we’re pretty comfortable with where we’re at. Handling the fish during the survey, the fish seemed healthy and robust. I think it was because of those high sustained flows over the summer. That was good for them. I think the fish in general are going into the winter well-fed and hopefully they have a better survival than normal.”

Of biggest concern to Fish and Game is how the Yellowstone cutthroat population is faring. The agency has been conducting rainbow trout suppression efforts during the spring, electrofishing and transferring the rainbows to other fisheries in an effort to reduce the rainbow population to about 10% of the total. Other measures include placing no limit on rainbows and rainbow hybrids and no harvest of cutthroat trout. To encourage keeping rainbows, coded wire tags are embedded into a small percentage of the rainbow trout heads that can be turned in for prizes ranging from $50 to $1,000.

Rainbow trout numbers are still well above goals. In the Conant reach, cutthroat trout comprised 43% of the total trout in the survey. Rainbow numbers are about 33% of the total with brown trout making up the remain 24%.

Kennedy said it may take a couple of years of electrofishing and transferring rainbows before they see more positive results.

This fall, Fish and Game also surveyed the Lufkin Bottom — an area on the river within the canyon of the South Fork near the end of the River Road. This section is surveyed every three years. In this section, the survey found 1,524 cutthroat trout per mile for about 34% of the total, 35.7% brown trout and 30.3% rainbow trout.

“The survey showed an increase in the number of brown trout in (Lufkin Bottom),” Kennedy said. “That’s not a concern so much for cutthroat. Brown trout throughout the South Fork seem to be fairly stable.”

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