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Thousands Of Kokanee Flushed Through Dworshak Dam Into Clearwater; Keep All The Fish You Can Catch
Posted on Friday, March 25, 2011 (PST)

Central Idaho anglers are enjoying a kokanee bonanza these days thanks to the inadvertent flushing of thousands of fish through Dworshak Dam into the North Fork of the Clearwater River below.


In response, the Idaho Department of Fish and Game immediately removed the bag and possession limits for kokanee in the North Fork Clearwater River and Clearwater River downstream of the North Fork in Clearwater County, effective through May 15.


The intent is to allow recreational fishers to salvage kokanee that are dead or dying as a result of going down through dam’s turbine units and regulating outlets that are now being used to spill water and help bring down the elevation of the reservoir.


Many of the kokanee, which are landlocked sockeye salmon, survived as well and are being taken by dip nets and rods and reels.


“One day we had about 130 live kokanee” in a salmon smolt trap downstream in the Clearwater River, said Joe DuPont, fish manager for the IDFG’s Clearwater Region. The trap was being used for research purposes to collect juvenile salmon that are migrating toward the Pacific Ocean.


DuPont said that, since the trap has a collection efficiency of only a few percent, a 130-kokanee total likely means that as many as 8,800 live kokanee passed downstream that day, which produced the peak collection of the past two weeks.


“The fish are getting flushed out of back eddies” and going downstream, DuPont said. And some might have got the notion, as kokanee occasionally do when given the opportunity, to head for the ocean like their sockeye kin. Kokanee generally spend their lifetime in freshwater.


Some of the washed out kokanee are 2-year-olds that would have headed up reservoir tributaries later this year to spawn and others were 1-year-olds.


While anglers can take home as many kokanee as they can carry, the fish may only be taken by rod and reel, dip net or by hand. A valid Idaho fishing license is required. It is Fish and Game’s intent to allow the public to harvest these fish using techniques that will not affect ongoing fisheries.


DuPont said that one surveyed angler took home 250 kokanee.


Kokanee, which are a popular target of anglers fishing at Dworshak Reservoir, tend to congregate near the dam during winter months. With mountain snowpacks quickly building in recent weeks the U.S. Army Corps of Engineers, which operates the dam must send enough water downstream to make room for spring runoff and make sure the project has the prescribed flood control capability. The higher the expected runoff volume, the lower the reservoir must be drawn to provide flood control space.


In this case, the Corps increased discharge to full powerhouse capacity, about 10,500 cubic feet per second on March 1 and on March 4 began spilling water as well, at first from 1.8 to 1.9 kcfs and then to 3.3 kcfs on March 10. In recent days the spill reached as high as 4.2 percent.


The goal is to drop the reservoir from 1,573 March 1 to 1,451.4 on April 15. That April 15 flood control target is just six feet higher than the maximum drawdown allowed.


“We’re drafting down to a much deeper elevation that we have recently,” the Corps’ Steve Hall said. That lowering elevation brings the kokanee, who like to huddle in the deep water close to the dam in winter, closer to the turbine outlets and regulating outlets.


Hall theorized that the sheer numbers of kokanee and their proximity to the outlets led to the “entrainment” of many of the fish.


DuPont says that entrainment is not unprecedented. In 2006 nearly the entire population of the reservoir was flushed downstream.


“Every year you’ll have kokanee entrained but not in these numbers,” DuPont said while adding that no one has an estimate yet of how many fish might have been flushed.


Both passage routes pose dangers for the kokanee.


“I really don’t know what route is the most difficult for fish,” Hall said. The ROs spill water down from about halfway down the 700-foot-high face of the dam. It sends the fish from pressurized reservoir atmosphere (many of the fish were likely under more than 100 feet of water) to a stream condition with only atmospheric pressure.


At this point, the number of kokanee being flushed is not expected to have a large influence on next year’s fishery. The IDFG estimated last year that the reservoir held one of the larger crops of kokanee in recent years, more than a million. DuPont said the IDFG figures it could have lost up to a third of the population downstream and still have a strong fishery this spring and summer.


The IDFG and Corps have for the past four years implemented a nutrient enhancement program that is intended to bolster the food supply for kokanee and other fish. It is in the coming years expected to bolster kokanee production in the reservoir by enabling more robust fish that produce more offspring.


For more information regarding the lifting of the kokanee bag and possession limits, contact IDFG’s Lewiston office, 208-799-5010.


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