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Though Kokanee On Rebound In Lake Pend Oreille, No Evidence Higher Lake Elevation Beneficial
Posted on Friday, November 01, 2013 (PST)

It’s back to the past for operations at northern Idaho’s Albeni Falls Dam, which has over the past decade been manipulated on the assumption that maintaining a higher wintertime elevation of Lake Pend Oreille would enhance shoreline spawning of prized kokanee salmon.

Idaho Fish and Game officials say that, after several years of study, they have not positively identified a benefit for kokanee from maintaining the lake elevation at 2,055 feet.

There may be a benefit, but research to date has not nailed down justification for operating Albeni Falls to maintain the higher lake level.

Such operations limit the flexibility of the U.S. Army Corps of Engineers to operate the dam for flood control and to generate hydro power on market demand. The Bonneville Power Administration markets power generated at the dam.

Research “failed to show a benefit from that extra four feet of water,” the IDFG’s Andy Dux said of a program that held the lake level in most years at 2,055 feet instead of historic drawdowns to 2,051 feet.

The good news from the Pend Oreille River system is that kokanee populations are on the rise, thanks to Mother Nature, perhaps, and a predator control program that has greatly reduced the number of large lake trout that munch on relatively small-sized kokanee.

The kokanee, a non-native species, were a prized angler target that also provided food for native bull trout, which are now protected under the Endangered Species Act, as well as introduced Gerrard rainbow trout and lake trout. The latter two species grow to trophy size.

The trouble is, populations of targeted kokanee began to swoon. At the end of the 1990s, kokanee populations started to drop at the same time that the lake trout population started to spike upward.

The kokanee population fell to as few as 5,000 estimated spawners in 2007. Up until the mid-1960s annual harvests of more than 1 million kokanee were common.

The once numerous kokanee population started to declinein the mid-1960s, coincident with modified Corps operations at Albeni Falls and with the introduction of mysis shrimp to the lake. The annual lake drawdowns result in diminished spawning area for the fish, according to the IDFG. The mysis, intended as a food source for kokanee, can instead compete with young kokanee for zooplankton. The small shrimp also helped fuel the lake trout explosion by providing plenty of food for the juvenile predators.

But the trends have reversed. Thanks to a sport reward program promoted by the state that pays anglers for catching and removing lake trout, and a targeted gill-netting program, a large share of the predators have been removed. And estimates of kokanee spawner numbers have been steadily increasing since they reached that all-time low in 2007.

“We’ve got the anglers and the netters working out there,” said the IDFG’s Andy Dux. “Both adult and juvenile [lake trout] are showing signs of continued decline.”

Dux said that surveys done in September indicate kokanee population levels are 20 percent higher this year for all age classes of kokanee.

“There is overall kokanee abundance that we haven’t seen since the ‘90s,” Dux said. The upward trend allowed the state to open a six-fish daily bag limit fishery for kokanee this year. It was the first kokanee fishery since 2000.

The return of kokanee harvest opportunity has been a welcome addition to the Pend Oreille fishery this year. While anglers are limited to a daily harvest of six kokanee in Pend Oreille, anglers have been taking advantage of the fishery and have generally had little difficulty finding good schools of kokanee and catching limits of 10- to 12-inch fish.

“We had a lot of folks that participated,” Dux said. And most were successful in catching their limit.

Meanwhile, the lake’s rainbow trout, initially targeted by gill netters and sport rewards programs, perhaps have benefited from the reduction in competition by lake trout. The state began in 2006 paying a $15 bounty to anglers for each lake trout and rainbow over 12 inches taken from the lake. The idea was to ease the pressure on kokanee by removing more of the larger fish predatory fish.

The state this year decided to remove the sport bounty on the rainbow trout, another favored angler target.

An October fishing derby was won with a 19-pounder. And there have been numerous reports from anglers of rainbows weighing more than 20 pounds, Dux said.

“It’s all about the kokanee,” which provide food for the big Gerrards as well as native, ESA-listed bull trout.

Lake Pend Oreille’s winter level is managed by the Corps after coordination with various federal, state, local and tribal officials. Since 1996 winter pool levels were set to benefit reproduction of kokanee salmon.

This year’s decision is not directed toward kokanee, however, as the species’ spawning ecology is being reexamined by the Idaho Department of Fish and Game, according to the Corps. The decision is in keeping with flood risk management needs and supports “Flexible Winter Power Operations,” which allow maintenance of the reservoir elevation between 2051 and 2055. That allows the Corps to respond to weather conditions and power demand.

The Albeni Falls flow schedule this year intends to draft Lake Pend Oreille to within a half foot of the minimum control elevation of 2051 feet by Nov. 10.

The winter MCE was officially set at 2051 feet for the winter of 2013-2014 during a Sept. 19 lake level meeting. The lake level as of midweek was, as measured at Hope on Pend Oreille’s north shore, is 2053 feet.

The Fish and Game research crew recently finished conducting the field portion of their kokanee population estimates. Analysis of the finding hasn’t been finalized, but the number of all age classes of kokanee continues to be very encouraging.

Rainbow anglers are also delighted with the abundant kokanee population, considering that more kokanee means faster growing and larger rainbow.

Through October 2013, the netting program has removed more than 8,100 lake trout from Pend Oreille, and Angler Incentive Program has accounted for an additional 3,147 lake trout removals this year. Since 2006, the two programs have removed over 162,000 lake trout.

Netting catch rates for lake trout have declined substantially since the program was initiated, Dux said. Standardized trap net catch rates are the primary index used to track changes in adult lake trout abundance and have declined more than 80 percent since the programs began in 2006. In addition, gill net catch rates for juvenile lake trout (primarily ages 2-4) have declined by over 75 percent since 2009, which is when they first were targeted with small mesh nets.

Angler catch rates are not available, but total catch has declined, likely because of a dwindling number of lake trout.

And while kokanee abundance has appeared to take a corresponding rise, bull trout have also shown some signs of improvement, Dux said. Standardized trap net catch rates for bull trout have approximately doubled since 2007. The responses observed to date suggest that suppression of lake trout can be achieved and provide benefits for both kokanee and bull trout.

“For this to happen, exploitation of lake trout at or above current levels needs to be sustained in coming years,” Dux said.

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