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Cascade Pikeminnow Will Be Trapped

Fish and Game plans a new approach to restoring Lake Cascade fisheries to their former glory.

Cascade Reservoir offers anglers a variety of game fish including large trout, coho salmon and tiger muskie but its main claim to fame is yellow perch. About 528,000 perch were caught there in 1986 when Cascade was attracting more than 400,000 hours of fishing and adding $4.5 million annually to the Idaho and local economy. The perch fishery collapsed completely by the late 1990s, with an accompanying decline of angler use to fewer than 60,000 hours each year since.

Fish and Game fisheries biologists sought explanations for the demise of the perch as soon as it was noticed. Several ideas were tested, including the discovery of a parasite that was finally recognized as harmless to the fish. Perch went over the dam by the hundreds of thousands in the early 1990s but that was determined to be an effect of having a huge population in the lake, not a cause of the decline. The abundance of food was considered but found adequate. Water quality, though nutrient-enriched in Cascade Reservoir, was found not to limit juvenile survival.

Biologists recognized the problem: extremely low juvenile perch survival since 1990. When the last of the big, old perch left the waters of the reservoir, perch fishing was at an end. Where did the young perch go? Down the gullets of Cascade's large, prolific northern pikeminnow population, according to regional fisheries biologist Paul Janssen. Northern pikeminnow often become overly abundant in the warm, shallow waters of altered environments of reservoirs.

Janssen explained his conclusions and proposed remedies to the Fish and Game Commission in January. He told the Commission the department would work to remove as many pikeminnow as possible from Cascade.

Poisoning the pikeminnow is the easiest fish management option, but the sheer volume of nutrients half a million dead pikeminnow would release at one time to the reservoir could be undesirable. Removing dead pikeminnow from the reservoir completely would not only reduce their predation on perch but also reduce nutrients in the reservoir, improving water quality.

Catching the pikeminnow (as well as large suckers) on their spring spawning run into the North Fork Payette River and Lake Fork Creek can trim their numbers and, presumably, allow perch to come back. That's the plan. It will be the largest operation to trap and remove undesirable fish ever attempted in Idaho.

Blocking these streams during the spring spawning run is not practical, partly because of large debris carried in the runoff. Special portable electric weirs that bar fish movement but allow streamflow will be required.

Once trapped, the pikeminnow and suckers will be removed from the waters and hauled out of the drainage. Fish and Game has received two proposals for final disposal of the fish. One proposal calls for composting them for fertilizer at a farm and the other is to ship them to the Midwest where they would be used for human consumption.

The trapping operation is slated to begin in May this year.