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Where we are in the fishery

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Unless the lake trout population is kept low over an extended period of time by some extensive harvesting measures, the lake trout will come back.

This is a story about the harvest of predatory trout in Lake Pend Oreille. How did the anglers do in the effort to reduce the predation on the last lingering age groups of kokanee? 

 In a report to the Lake Pend Oreille Fishery Recovery Task Force, (of which your author is a member) the IDF&G provided these numbers which included nine months of 2006 and one month of 2007.

For 2006-2007, 6,072 Rainbow were harvested by anglers.

For 2006-2007 11,456 lake trout were harvested by anglers, for a total angler harvest of 17,528.

The net harvest in the fall of 2006 resulted in 4,431 lake trout, 18 Rainbow, 2,363 pike minnow, 60,173 and 288 Bull Trout. The whitefish and Bull Trout were released alive; all other species were killed.

Tag returns from marked rainbow provided significant information to estimate rainbow trout population. In December of 2006 IDF&G statistical analysis estimated the overall population of rainbow was 35,384 with 19,091 of those exceeding 16 inches in length. Anglers had greater success in spring fishing than in the fall effort. In the spring a bit over 500 rainbows caught were 14 inches long, 425 were 17 inches long, and 200 were 20 inches long. The catch curve showed almost none under 12 inches and only a handful over 30 inches. The vast majority harvested were between 14 inches and 24 inches in length. This was true for both spring and fall fishing reports.

The estimates of the percentage of harvest to total population were calculated at 23 percent for rainbow and 45 percent for lake trout. When natural mortality is added, it brings the rainbow mortality to 39 percent and to 60 percent for lake trout. The target for harvest of both species was 50 percent.

 Dr. Mike Hansen, Professor of Fisheries from the University of Wisconsin, has developed a model for predicting what it would take to reduce the lake trout population to almost nothing. The reason this is so important is because we know there is no lake in North America that has a combined fishable population of lake trout, rainbow trout, bull trout and kokanee. Lake trout simply will not coexist with those species. Lake trout do coexist with whitefish, grayling and spiny rays species (bass, perch, etc.). On the other hand, rainbow, bull trout and kokanee can coexist in cold water lakes. That is why it is so important for the return of kokanee and trophy rainbow fishing to exploit the lake trout population to the point of collapse.

Dr.. Hansen’s model predicted it would take five years of combined angler and net harvest of lake trout to reach the point of lake trout collapse. The model assumes the percentage of the population remaining is harvested at the same rate each year. The number of fish caught will decline as the total population declines but the percentage of harvest is the same. 

Unless the lake trout population is kept low over an extended period of time by some extensive harvesting measures, the lake trout will come back. The environment for lake trout in Lake Pend Oreille is so good it will not be possible to eradicate them. 

Lake trout have a huge spawning habitat to use. Lake trout fry have an almost unlimited food source in the mysis shrimp and therefore lake trout fry will have a high survival rate. The struggle to limit lake trout population will persist. 

Discussions on how to keep harvest pressure on lake trout have been directed at several potential options. Continued netting is expensive and might not be eligible for subsidizing at the same rate as now. Angler incentives might be increased to target the smaller lake trout. 

It could be possible to authorize a commercial harvest of the plentiful whitefish with the understanding that lake trout caught in the same nets as whitefish would be killed for human consumption. Lake whitefish can withstand substantial harvest annually without causing significant reduction in their population because their spawning habitat is excellent, they grow to sexual maturity quickly and they are not heavily targeted by sports fishermen. 

The advantage of a commercial whitefish program is that the market place would provide the money needed to replace the present trap net subsidy. Whitefish are quite abundant and would provide a profitable prospect for a commercial fishery. However, this is only one of several options on the discussion table. 

Idaho Fish and Game has applied to the Clark Fork Settlement Agreement’s management committee to fund the angler incentive program for 2007, as well as extending the fall net fishing for lake trout. A good case for funding can be made because anglers really did make serious inroads in the predator population. Rainbow will be legal targets in the tributaries of the lake all winter and spring. Biologists hope anglers will pursue the larger rainbow in these tributaries, especially in March and April. That could bring the rainbow harvest up to the 50 percent target.

What has all this fishing and net pressure done for the kokanee? We do know there are 17,528 fewer mouths eating kokanee today. But is that enough to raise the kokanee survival up to the levels needed for recovery? 

We do not know the answer today. It will be early in September before Dr.. Maiolie finishes his hydro acoustic survey of kokanee. He will then know how many fry have survived for the few months after emerging from spawning bed gravels and hatchery release. The critical count will be the number of age 1 that survived to age 2 and that is what we really want to see go up. 

Survival of age 1 to 2 needs to approach 50 percent in order to say we have turned the corner to kokanee recovery. It would be wonderful if the survival of age 2 to 3 would also go up to 50 percent. Since there are significant numbers of age 3 kokanee that make their only spawning run, we cannot expect survival of age 3 to 4 to be very high. If kokanee are restored, Lake Pend Oreille will be the first lake ever to overcome a lake trout dominated body of water and restore the kokanee. If this happens it will be due to the perseverance of the area’s fishermen and cooperation with Fish and Game biologists.

There may be light at the end of the tunnel. Until September we all should keep up the fishing pressure, hope the angler incentive program is funded again and keep turning in those fish heads.

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Author info

Hobart Jenkins

Tagged as:

Lake Pend Oreille, fishery, Idaho Department of Fish and Game, lake trout, Lake Pend Oreille Fishery Recovery Task Force

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