Studies: Higher winter pools don't aid kokanee

SANDPOINT — The proposition that a higher winter pool on Lake Pend Oreille enhances kokanee survival has gone belly-up.

That’s one of the upshots of more than two years of study conducted by the University of Idaho and the Idaho Department of Fish & Game

“We didn’t find any evidence that the water level — a 4-foot increase — was affecting egg survival,” Andy Dux, a fisheries research biologist with Fish & Game, told the Pend Oreille Basin Commission on Friday.

The university and the department began taking a closer look at kokanee egg survival after finding that survival rates were still high even when the lake was drawn down to 2,051 feet above sea level.

The first year of the study revealed that deep-water spawning is viable and occurring in Lake Pend Oreille and that kokanee were also spawning in finer gravel substrate at Scenic Bay with high rates of success, contrary to long-held notions that kokanee preferred to spawn in coarser substrate.

Dux said the study concluded that “downwelling” currents that charge the Spokane Valley-Rathdrum Prairie Aquifer at the south end of the lake were conducive to kokanee spawning in substrate that initially appeared unsuitable.

It was initially believed that finer sediments would suffocate eggs, but Dux said the study suggests that water percolating down to the aquifer was bringing oxygen to the eggs.

“That was pretty eye-opening and something we didn’t know prior to this study,” Dux said.

The second year of the study involved the placement of more than 300 plastic mesh egg boxes at 60 locations around the lake, which seemed to confirm downwelling and dissolved oxygen aids kokanee recruitment.

“We found that we had about a 30-percent increase in survival for every one milligram-per-liter increase of dissolved oxygen we saw, so that was pretty substantial. We also saw there’s about a three-times higher survival rate when downwelling was present,” said Dux.

Fish & Game intends on conducting a pilot study next year to see if moveable substrate can be spread over immovable substrate to enhance spawning habitat at Idlewilde Bay.

The studies conducted by the department and the university will also undergo peer review to vet their reliability.

Although the studies are enlightening kokanee recovery efforts, Dux said the department can no longer justify recommending a higher winter lake level, which is the elevation preferred by Bonner County residents because it facilitates recreational access and tourism.

The research discoveries come at time when the water in Lake Pend Oreille is coveted by the Bonneville Power Administration and various other downstream interests.

“The stakeholders around Pend Oreille are probably the only people who are going to be advocating for a higher lake level in a given year. Everyone else is going to be basically just frankly saying, ‘Take it down,’” said basin commission Chairman Ford Elsaesser.