Regional fisheries biologists recently crunched the numbers on their spring electroshocking efforts and report removing 10,654 rainbow trout from the South Fork of the Snake River and stocking them in other East Idaho waters.

The goal of the Rainbow Trout Suppression project on the South Fork was to remove 30 percent of the rainbows — about 12,000 fish — to give the native cutthroat a better chance to thrive.

Pat Kennedy, regional fisheries biologist heading up the Idaho Fish and Game project, said, although the project starting April 19 and ending May 27 didn’t reach the goal of 12,000 rainbows, when added to the Rainbow Trout Harvest Incentive Program, the added angler harvests push the total numbers of rainbows removed from the river to 12,047.

Success of the program won’t be known until Fish and Game’s annual fall survey of the river.

“In general, we have achieved that 12,000 fish, which is 30 percent of the last year’s abundance assessment,” Kennedy said. “It’s really great that anglers have contributed to that management goal to the conservation of cutthroat.”

An October survey of the South Fork found trout numbers at record levels of 6,302 fish per mile in the upper river. Rainbow trout numbers made up 43 percent of the total in the Conant reach. Fish and Game’s management goal for the upper river is 10 percent or less rainbows to reduce competition with native cutthroat trout and to prevent hybridization — cutthroat and rainbow trout are both spring spawners.

Fish and Game biologists manned two to three boats on different stretches of the South Fork between Palisades Dam and Conant Valley. Each day they stuck to a specified area to avoid conflict with anglers plying the popular fishery.

“Just so anglers could work around us we were always in the same place on the same days of the week,” Kennedy said.

Boats typically had two netters and one operator. Netted rainbows were placed in livewells and scanned to see if they had a coded wire tag indicating they were a prize fish. Fish with tags were put back in the river to encourage future angler harvest. Anglers can turn in fish heads for rewards ranging from $50 to $1,000. At the end of the day, the rainbows in the livewells were transported to the Henrys Fork or area fish ponds. Fish and Game reported 2 percent mortality of rainbows during the operation.

The suppression efforts were conducted during the spring to take advantage of rainbows gathering to spawn.

One distant area restocked with South Fork rainbows was the upper Big Lost River.

“This was a response to anglers wanting more fish in the upper Big Lost,” Kennedy said. “They’ve caught some of those fish. We got some good feedback from some of those anglers that they are catching some real high quality South Fork rainbows. They were in their spawning periods so we’re hoping that they reproduce and supplement some natural production.”

Kennedy said the electro shocking operation averaged netting 1.4 rainbows per minute. The average size of the trout were 15.7 inches and 1.6 pounds. Trout in the upper sections nearer to Palisades Dam were slightly larger — 16.1 inches and 1.7 pounds on average.

Most of the 10,654 trout were restocked into the Henrys Fork in four different locations: at Del Rio Bridge (1,622), the railroad trestle bridge downstream of St. Anthony (1,969), Warm Slough Campground (1,986), and Beaver Dick Park (1,423). About 100 of the rainbows restocked at Beaver Dick Park were tagged with T-bar “Tag, You’re It” tags. Anglers who catch the fish can call in and report when and where they were caught.

“Through that we’re hoping to better understand where these fish move and if they benefited the anglers in those fisheries,” Kennedy said.

Fish and Game also wants to know if any of the relocated rainbows make their way back into the South Fork where they don’t want them to be. Kennedy said he doesn’t expect they’ll return to the South Fork.

“There seems to be a really warm area downstream from Beaver Dick Park still on the Henrys Fork and they really don’t like to move through that,” Kennedy said. “It’s a sandy and warm habitat. We’re hoping that they stay up in the Henrys Fork.”

Electro shocked rainbows were also restocked in the Jim Moore Pond near Roberts (1,095), the Trail Creek Pond near Victor (581) and Louis Pond in Swan Valley (647).

Electro shocking and removing rainbows from the South Fork brings a mixed reaction from anglers.

“On the water we’d see some people that are strongly in favor of what we’re doing. In my opinion they are the non-vocal majority,” Kennedy said. “But we did get some negative feedback. Some anglers may have been frustrated with us. If we shock in front of them there’s this perception that electrofishing can reduce catch rates. If you’re a rainbow trout fisherman, we might have reduced catch rates. That’s an unfortunate side effect of our major objective to remove rainbow trout.”