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Bull trout "flip" over Cabinet Gorge Dam.


Since 1952, Cabinet Gorge Dam on the Clark Fork River has blocked fish from migrating from Lake Pend Oreille, the largest lake in Idaho, into most of western Montana. Among those fish were hundreds, perhaps thousands, of native bull trout (Salvelinus confluentus).

In 1998, the Service listed the bull trout in the Columbia River drainage (including the Clark Fork River) as threatened due to habitat degradation, passage restrictions at dams, and competition from non-native fish. The loss of connectivity between headwater spawning and rearing streams and the productive downstream waters of Lake Pend Oreille was identified as one of the most significant factors limiting the recovery of bull trout in the Clark Fork River drainage.

Bull trout are large migratory char of the Pacific Northwest. They often grow to maturity in lakes and swim upstream, sometimes over 100 miles (160 kilometers), to spawn in the small streams where they were born. Their life cycle is similar to that of salmon, except that Lake Pend Oreille functions as an inland ocean and bull trout don't die after spawning. The world record bull trout, a 32-pound (14.5-kilogram) fish, was caught at Lake Pend Oreille.

The Clark Fork River is the largest river flowing from Montana, and it drains most of the western landscape of that vast state. For 50 years, fish migrations in the Clark Fork River were blocked by a series of dams. In 1999, however, the Avista Corporation and the Fish and Wildlife Service formed a partnership to develop fish passage methods at Cabinet Gorge Dam. The Service provides the lead biologist, while Avista provides funding and other biologists to carry out a variety of recovery actions. In 2005, after a four-year experiment involving the passage of 140 large adult bull trout upstream over the dam, biologists concluded that the method was successful. The long-term conservation efforts committed to by Avista and the Service in 1999 reflect a mutual desire to recover bull trout while facilitating the production of electricity at dams on the Clark Fork River.

As part of the experiment, radio transmitters were surgically placed inside the bodies of bull trout to allow biologists to follow their movements. From 2001 to 2004, about 35 fish each year were captured below Cabinet Gorge Dam and trucked to release sites upstream. The fish then swam upstream to a tributary, the East Fork Bull River, where they spawned, mixing with other bull trout that had resided in the Cabinet Gorge Reservoir throughout their lives. About half of the transported bull trout survived the rigors of spawning. Following the spawning season, biologists used weir traps to recapture some of the survivors. They were given a free ride back downstream and released into the Clark Fork River below Cabinet Gorge Dam. Other bull trout swam back down the Bull River on their own, making their way through the reservoir and the dam turbines back to Lake Pend Oreille. Radio tracking determined, to our surprise, that more than half of the fish that passed through the dam turbines survived.

These fish transfers have increased the number of spawning bull trout in several streams that had extremely depressed populations. Since each adult female can carry as many as 10,000 eggs, the potential boost to the population from just a few large spawners can be significant.

In 2004, the Service used new technology to take the program to a new level. Collaborating with Avista, it developed a rapid response genetic assignment method to determine the stream of origin for bull trout captured below Cabinet Gorge Dam. This method involves rapid processing of a genetic sample from a small piece of fin. Within 48 hours, the results are used to "assign" individual bull trout, based on their genetic profile, to the stream in which they hatched. In the future, this method will allow biologists to transport fish captured below Cabinet Gorge Dam to appropriate release sites above any of the three dams on the lower Clark Fork River. Drs. Don Campton and Bill Ardren from the Service's Abernathy Fish Technology Center developed and manage the genetic program.

The partnership of the Service and Avista on the lower Clark Fork River offers exciting promise in support of the eventual recovery of bull trout. The innovative fish trapping, transport, and genetic assignment techniques developed in this project will have broad application for conservation of bull trout and other rare fish species throughout the country.


Larry Lockard is a fish and wildlife biologist at the Service's Creston Fish and Wildlife Center in Kalispell, Montana 59901 (telephone 406/758-6883).
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Author:Lockard, Larry
Publication:Endangered Species Bulletin
Geographic Code:1U8MT
Date:Mar 1, 2006
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