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Lake Pend Oreille Kokanee Numbers Up Due To Efforts Reducing Lake Trout By 80 Percent
Posted on Friday, November 16, 2012 (PST)

Anglers on north Idaho’s vast Lake Pend Oreille will next year likely get to target kokanee for the first time since 2000 when fisheries for the land-locked sockeye salmon were closed because of plummeting populations.

Upward trending kokanee populations have prompted an Idaho Department of Fish and Game recommendation that a limited kokanee fishery be offered in 2013 in the state’s largest (148 square miles) and deepest (1,150 feet) lake. The fishing regulations must be approved by the state’s fish and wildlife commission.

The rising numbers – expected to be the highest since 1996 -- result in large part from a state effort to remove a non-native predator – lake trout – that has been feasting on the kokanee.

Lake Pend Oreille “historically was the most heavily used fishery in Idaho,” Chip Corsi, supervisor for the IDFG’s Panhandle Region told the Northwest Power and Conservation Council during last week’s meeting in Coeur d’Alene.

The targets included native bull trout (a stock now protected under the Endangered Species Act), westslope trout and mountain whitefish. Introduced kokanee became one of the favorite angler targets, as did introduced Gerrard rainbow trout, which can grow to trophy proportions. Up until the mid-1960s annual harvests of more than 1 million kokanee were common.

But 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 dropped to a low of only 5,000 estimated spawners in 2007.

“We want to bring the kokanee fishery back,” Corsi told the Council. A revival should also help bolster bull trout and the lake’s Gerrard rainbow trout. Kokanee were historically a mainstay of those bigger species’ diet.

“We generally view lake trout as bad neighbors,” Corsi said of a fish species that was introduced to the lake.

Much of the IDFG work related to a kokanee has been funded by the Bonneville Power Administration through the Council’s Columbia River Basin Fish and Wildlife Program as mitigation for federal hydro system impacts. Albeni Falls Dam, which backs up the Pend Oreille River to expand the lake, is part of the federal hydro system.

Avista, a Spokane, Wash.,-based, investor-owned utility that provides power to its customers with a mix of hydro, natural gas, coal and biomass generation also provides funding for the work, which has since 2006 attacked the lake trout population with fishing nets and with cash rewards for sport anglers who pull the large, voracious fish from the water.

Since 2006 a total of 143,381 lake trout have been removed from the lake, 69,742 by angling and 73,639 with nets deployed by hired fishermen. Those numbers are through August and do not include fall data. The netting will be ongoing until December.

“The key is that both netting and anglers have played a key role in reducing the population,” said Andy Dux, principal fishery research biologist.

Data showing trap net catch rates are used in the research as an index to adult abundance.

“Basically, we have reduced the number of adult lake trout by well over 80 percent since 2006 when the program started,” Dux said. “Also, in recent years we’ve learned how to target juvenile lake trout and have seen catch rates for those fish decline by about 60 percent.”

Likewise, anglers have also been removing fewer fish in recent years as the population has declined.

“All together, these things point toward a substantially reduced lake trout population,” Dux said.

Meanwhile, kokanee have been steadily increasing since they reached that all-time low in 2007.

“Last year they had rebounded to about the level they were at in 2000 when we closed the fishery,” Dux said. “This year we saw a bigger incremental increase in the population and our estimates for age 1-5 kokanee (all ages combined) is the highest it has been since 1996.” The kokanee populations remain at levels well below the more distant past, but are trending in that direction.

“This gives us confidence that we can provide a limited harvest fishery (6 fish daily) starting in 2013,” Dux said.

“We’re taking a baby step,” Dux said of what is a relatively low daily bag limit. Things should get better. The smaller fish, the 1 and 2 year olds, are now the most numerous age classes and should provide more fishing, and more natural production, in the future as they grow older.

The IDFG is also proposing that the state remove the sport bounty on the rainbow trout. The state began in 2006 paying a $15 bounty to anglers for each lake trout and for rainbow trout over 12 inches taken from the lake. The idea was to ease the pressure on kokanee by removing more of the larger predatory fish.

“But, the incentive program has not been as effective for rainbows as it has been for lake trout,” Dux said. The lake trout tend to linger nearer shore in shallower water and are thus easier to find and net or catch.

With the lake trout population greatly reduced and the kokanee population increasing, the IDFG feels that the kokanee and rainbows can now coexist as they did in the days before the lake trout blossomed.

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

“Rainbow trout have remained fairly stable, despite the angler incentive program,” Dux said. “We were not able to reach harvest rates that were high enough to drive abundance down.

“And, now that kokanee have sufficiently rebounded to reduce the threat of their population collapsing, we feel that removing the anglers incentive for rainbows is appropriate and will gradually transition back towards management for a trophy rainbow trout fishery.”

Bull trout populations have also remained stable.

“This is a victory considering that lake trout posed a major threat to bull trout,” Dux said.

“We hope that with fewer lake trout and more kokanee that bull trout will be able to increase in abundance in coming years.”

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