Cutthroat trout come out ahead in electrofishing study

Trout by the numbers

Statistics of the Conant stretch of the South Fork of the Snake River:

Trout per mile

• 2015: 4,032
• 2014: 3,671

Yellowstone cutthroat trout per mile:

• 2015: 1,724
• 2014: 1,487

Rainbow trout per mile

• 2015: 1,052
• 2014: 1,418

Brown trout per mile

• 2015: 1,256
• 2014: 765

Study conducted by Idaho Department of Fish and Game.

SWAN VALLEY — Cutts are up, bows down. That’s just what researchers want when they survey the South Fork of the Snake River every fall. The results back up efforts to keep rainbow trout from taking over the native cutthroat trout fishery.

“I’m excited. It tells me we are making headway,” said Brett High, Idaho Department of Fish and Game regional fisheries biologist. “The last few years we’ve been looking at results with rainbows staying steady and cutthroats staying steady. We were just holding the line the last three or four years. This year we are seeing a change.”

Idaho Department of Fish and Game uses electrical current to stun fish for population counts on the Conant stretch of the river, one of the oldest surveyed stretches of water in Idaho.

Multiple days of collecting fish turn into multiple weeks of tallying stats to figure out how many fish per mile are in the river and what kind of fish are in those miles.

In 2015, Yellowstone cutthroat trout per mile increased from 1,487 in 2014 to 1,724. The number of rainbow trout per mile decreased from 1,418 in 2014 to 1,052. Rainbows can spawn with cutthroats, diluting the native cuttie population. That’s why the department tries to keep rainbows in check with a spring flush pushing rainbow beds out of place, improved tributaries for spawning cutthroats and a cash tag incentive for anglers harvesting rainbows.

“It looks like management is having an impact, and that impact is aiding our native Yellowstone cutthroat trout,” High says. “It’s just a proven fact that without intervention in a situation where rainbows live with cutthroats, over time you will lose those cutthroat.”

Cutthroats are not losing on the South Fork right now, and nor are browns. The brown trout population is up at 1,256 per mile in 2015 compared to 765 in 2014. Browns don’t spawn with cutthroats, but they can compete with them. The growing brown population is not warranting any action yet, but High has his eye on the trend.

“(Browns) have always done their own thing at Conant, but across the West they have an impact on cutthroats,” High said. “We’re confident browns play nice with cutts here. Their trends don’t impact cutts on the South Fork, but in the last 10 years, there has been a trend overall that brown trout numbers are increasing. If that trend continues, we’re going to have to investigate the impacts.”

Total fish per mile is also up increasing from 3,671 trout per mile in 2014 to 4,032 in 2015. Those stats prove you can’t blame the river for your fishless days.

“It’s a very productive river. It’s amazing,” High said. “Everything ties back to this survey. We work all year at trying to help cutthroat and this is our one peek into how things are going each year.”

Surveys on the Conant stretch of the South Fork started in 1982, when biologist Virgil Moore was in charge of eastern Idaho fisheries. He is now the director for the Idaho Department of Fish and Game.

Outdoor journalist Kris Millgate is based in Idaho Falls. See her work at www.tightlinemedia.com.