SANDPOINT, Idaho -- Idaho fisheries biologists are rethinking the formula used for years to set recommendations for winter lake levels at Lake Pend Oreille to boost kokanee salmon recovery.
Since the 1990s, the Idaho Department of Fish and game has pegged its annual recommendation for winter pool levels to egg-to-fry survival rates. But the reliability of that metric has fallen into question amid scrutiny of the data collected by the department.
Initially, survival rates ranged at expected levels of 6-to-15 percent, but those rates have grown higher recently even when the lake is drawn down to lowest levels, which reduces the amount of shoreline spawning habitat. The accuracy of the survival rate is important because it's the scientific basis for recommending a higher winter pool of 2,055 feet above sea level and the lower pool of 2,051 feet, according to a story published by the Bonner County Daily Bee.
"Three years in a row, we had these really high egg-to-fry survival rates -- so high that they weren't really even plausible," said Andy Dux, Fish & Game's principal fishery research biologist in the Panhandle.
The egg-to-fry survival rate takes into account several categories, including estimates of wild and hatchery fry abundance, sex ratios and the number of wild or hatchery spawning fish. Department officials say they remain confident in the accuracy of those individual categories, but have growing doubts about accuracy when all those factors are thrown into the same mix.
"The problem can come in when you start to combine all those things and the variation can compound itself," Dux said.
For the department, there are other factors to consider in making its winter pool recommendations.
For example, there are downstream interests in the lake's water, including power generation for the region and endangered chum salmon in the Columbia River.
A deeper drawdown typically satisfies the downstream interests but hampers recreational access to the lake and threatens to de-water shoreline spawning grounds used by late-run kokanee.
Fish and Game officials say kokanee recovery efforts are showing positive results and that the department has two years to develop new ways of justifying its lake level recommendations because of an agreement with the Bonneville Power Administration.