Science trumps speculation in kokanee debate

There is too much confusion about what the Idaho Department of Fish and Game is doing to help the kokanee in Lake Pend Oreille recover.

Mortality rates of kokanee were running about 34 percent in 1984. In 1994, the mortality rates had risen to 56 percent and in 2004, 75 percent of kokanee did not live to age 4 to spawn. Those are hard facts taken from hydro-acoustic tests done in August of each year.

No prey species can survive when the mortality rate is that high. In biological terms, that is called a "predator trap." The dreaded "predator trap has already occurred in Flathead Lake in Montana and in Priest Lake in Idaho. Lake Pend Oreille will be the next lake to lose its kokanee if nothing is done to reduce the predation.

Rainbow trout account for about 60 percent of the kokanee loss, lake trout 34 percent, bull trout about 4 percent, and the rest of the loss can be charge to pike minnow, ducks and seagull. However, the lake trout population is growing very rapidly. In 2004, the lake trout population of fish over 20 inches was estimated at 6,400 fish.

In 2006, calculations indicated the lake trout population was now over 10,000 fish. Rainbow populations were undetermined, but all indications are the rainbow population is stable but has fewer trophy fish and more 3- to 5-pounders.

The growing threat is coming from the rapidly expanding lake trout populations.

Experts from Midwestern states that have large lake trout populations to manage, and Canadian experts with experience in both lake trout and rainbow trout have told Fish and Game that kokanee are doomed unless trout predation on the kokanee is significantly reduced. All the experts agreed that both rainbow and lake trout will have to be fished heavily, and that netting would no doubt be required to suppress the lake trout population expansion.

Too few fishermen target lake trout to do the job. Maybe fishermen can cut back on the rainbow population enough to help the kokanee.

This spring, a group of people representing the charter boat operators, marina owners, sportsman associations and chambers of commerce are working together to create an incentive plan to convince fishermen to come to Lake Pend Oreille frequently to fish for these predators. There will be selective netting of lake trout to help reduce that population, but no more than half the present population.

These are drastic measures, but the loss of the kokanee is even worse. Rainbow will not grow to the over 20-pound trophy size because there will not be enough food for them to grow fast enough since their life span is only a third of lake trout. There are three generations of kokanee left in the lake. If predation is not reduced to under 40 percent, the kokanee will be functionally gone. Efforts to restore kokanee in Flathead have proven there is no way a stocking program can ever recover the kokanee.

The trap-setting project is where the lake trout are caught. Some of them are tagged before releasing them. Some of the tagged fish are caught again. This data give biologists the mathematics to calculate the population. The formula is M times C divided by R, where M equals the number of fish caught, C equals the number of tagged fish, and R equals the number of tagged fish that were caught for the second time.

It makes no difference whether the nets are placed in the same place in successive years since the formula only uses a count of the fish. The larger the number of fish caught, the better the formula predicts the total population.

So there it is, in cold, hard scientific facts. The kokanee will be lost unless unless we, the public, recognize that Fish and Game biologists, experts from Midwest states and Canada are right and accept the temporary reduction of both rainbow and lake trout in Lake Pend Oreille.

If you don't believe me, call the office of the Lakes Commission (Kate Wilson) at 263-7544, est. 3933.

HOBART G. JENKINS, Ph.D..

Bayview