SANDPOINT — The Idaho Department of Fish & Game is heading back to the drawing board to develop new ways to justify lake level recommendations that aid kokanee recovery.
Since the 1990s, Fish & Game has relied on egg-to-fry survival rates when making winter pool recommendations for Lake Pend Oreille. But the reliability of that metric has fallen into question amid closer scrutiny of the data collected by the department.
At first, survival rates bounced around at expected levels of 6-15 percent, but have recently become inexplicably higher even when the lake is drawn down to 2,051 feet above sea level, which reduces the amount of shoreline spawning habitat.
“Three years in a row, we had these really high egg-to-fry survival rates — so high that they weren’t really even plausible,” Andy Dux, Fish & Game’s principal fishery research biologist in the Panhandle, told the Pend Oreille Basin Commission on Friday.
The egg-to-fry survival rate is the product of a wide array of sub-estimates of wild and hatchery fry abundance, maturity proportions, sex ratios, wild and hatchery spawners, and fecundity. Each of those sub-estimates also have their own variations.
Although the department is confident about the accuracy of the sub-estimates on their own, it has growing doubts about the accuracy when all those 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.
The accuracy of the survival rate is important because it’s the scientific basis for recommending a higher winter pool of 2,055 feet and the lower pool of 2,051 feet.
Then there are the downstream interests in Lake Pend Oreille’s water, which include 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.
“Everyone else wants 2,051 except for us, right?” said basin commission Chairman Ford Elsaesser.
Elsaesser said it’s long been understood that a lower lake level limits the amount of spawning habitat.
“There didn’t seem to be a great deal of uncertainty in the past,” said Elsaesser.
But Fish & Game contends it needs a solid scientific footing to justify its recommendations to other state and federal resource managers.
“We have to take a look at these data that are driving these decisions,” said Chip Corsi, Fish & Game’s Panhandle region manager.
Corsi added that kokanee recovery is working and the department has two years to develop new ways of justifying its lake level recommendations because of an agreement with the Bonneville Power Administration which sets a higher pool this winter and a lower pool next winter.
Dux said a possible alternative could be to monitor direct incubation success by placing kokanee eggs at various levels of the lake in different spawning habitat conditions.
“It’s going to give us a lot more information about the effects lake levels are having in a fairly short time frame,” said Dux.
But members of the basin commission remain skeptical.
“It seems to me there is a lot of variables here that aren’t being taken into account,” said basin Commissioner Linda Mitchell.