Manmade barriers that have prevented resident fish from migrating upstream on the Big Lost River are no longer the obstacle they once were.
Last October, Trout Unlimited joined several other groups in retrofitting three irrigation diversion dams on the Big Lost with fish-passage structures to reconnect fish populations on several reaches of the river. Heavy equipment operators hired for the job did the delicate task of positioning large boulders and concrete barriers to create the fish-friendly passage structures.
Though the project will likely benefit more than one fish species on the high-desert river system, the intended beneficiary is an increasingly rare strain of native whitefish that only resides in the Big Lost.
The Big Lost River mountain whitefish, a freshwater member of the salmonid family, is a form of mountain whitefish found nowhere else in the world. Though they were once prolific in the river, by 2005 their population had declined to just two percent of its historic level, research by the U.S. Forest Service shows. The plight of the fish has also caught the attention of the Idaho Department of Fish and Game, which approved a rescue plan in 2007.
"We're concerned the fish not wink out," Steve Yundt, fisheries chief for Fish and Game, told Idaho Fish and Game Commissioners last year.
Fish and Game's conservation plan for mountain whitefish living in the Big Lost drainage calls for the preservation of two distinct populations of at least 5,000 adult mountain whitefish each, one above and one below Mackay Dam on the mainstem of the river.
Above the dam, the plan calls for a distribution of fish between the Chilly Slough diversion and the North Fork of the Big Lost River. And it calls for a population in at least three of the following four tributaries: the North Fork of the Big Lost, East Fork of the Big Lost, Wildhorse Creek and Star Hope Creek.
In each of those spots, the plan calls for a population of at least 100 fish.
Below Mackay Dam, the plan calls for a distribution of fish in the Big Lost River downstream to the Blaine Diversion, and in at least one of the following two stretches: the Big Lost River between the Blaine diversion and the Moore diversion, and Antelope Creek between Marsh Canyon and Iron Bog Creek.
The work by Trout Unlimited and its partners—which include landowners, the Big Lost River Irrigation District, the Salmon-Challis National Forest, Fish and Game, Natural Resources Conservation Service and the U.S. Fish and Wildlife Service—is an effort to reverse the declines by connecting isolated populations.
The in-river obstacles appear to be a key reason contributing to the fishery's troubling decline, according to Bart Gamett, a U.S. Forest Service biologist who worked closely with Trout Unlimited on the project. Gamett works out of the forest's Lost River Ranger District headquarters in Mackay.
"These diversions were significantly impairing the ability of fish to move through the Big Lost River," he said.
The new fish ladders and bypass channels, installed at the Blaine and Swauger diversions on the Big Lost River, and Antelope Creek, a large tributary to the Big Lost, will reduce fragmentation of critical habitat on the Mackay-area watershed, project backers claim. The say the bypasses will allow the native whitefish populations to move out of stream reaches that become uninhabitable and help them to complete their full lifecycle migrations.
Gamett's research has revealed a key problem for mountain whitefish: They can't jump like other species of sport fish. That wasn't true for cutthroat or brown trout that he tested for leaping ability.
Gamett found that Big Lost River mountain whitefish are unable to even get past small vertical drops or dam barriers that obstruct their upstream movements in the river.
Based on mitochondrial DNA research, it's believed that the Big Lost River mountain whitefish moved into the river system 165,000 to 330,000 years ago, Gamett said. The population has been cut off from other whitefish for thousands of years because the Big Lost sinks into the desert south of Arco. The subspecies is considered most closely aligned with the upper Snake River mountain whitefish, which is probably the parent stock.
The species' tenuous situation is a far cry from years ago, when locals considered the then-abundant whitefish an excellent adversary for mid-winter fishing.
A heavy equipment operator from the Big Lost River Irrigation District prepares to drop several large boulders in a fish-passage structure at the Blaine Diversion on the Big Lost River downstream from the Mackay Dam. The work, which is intended to help the imperiled Big Lost River mountain whitefish, a rare strain of whitefish only found in the Big Lost, was completed last October.
Photos courtesy of Trout Unlimited
