An effort this fall to find spawning lake trout, and their eggs, in north Idaho’s Lake Pend Oreille has come up empty.

Near-shore/shoreline surveys were intended give Idaho Department of Fish and Game biologists an early sign as to whether a new strategy to reduce lake trout numbers had worked. Columbia River basin fish managers in mid-September asked that the lake be held at full pool later than normal this year in hopes that lake trout would complete their spawning mission, and do it at higher elevations around the lake.

It was theorized that, when the annual lake drawdown began, the eggs would be left high and dry and reduce the fish’s overall reproductive success.

“We saw the occasional big fish dart away,” said the IDFG’s Melo Maiolie. But IDFG biologists scouting in the middle of the night with boats using underwater lights did not find congregations of spawners as they had expected. They hoped to identify spawning areas that can be later checked for desiccated eggs after the lake was drawn down to its winter flood control level.

The survey was carried out three to four nights per week during a three-week period in late September and early October. Crews covered about eight miles of shoreline each night. Only a handful of lake trout were spotted.

“We didn’t seem them spawning shallow. Does that mean they’re spawning deep?” Maiolie said.

“Either they weren’t there or we missed them,” he said. Spawning has been monitored in other water bodies, but not in Lake Pend Oreille. That research has shown that most spawning in smaller lakes takes place at relatively shallow depths, about two meters, Maiolie said. In large bodies of water, like the Great Lakes, the fish seem to prefer deeper water reefs.

“In general they would spawn shallow,” he said. The agency is considering capturing and radio tagging lake trout spawners next year so their movement can be tracked.

“We can revisit the drawdown thing” if those studies prove out the theory that Pend Oreille Lake trout lay their eggs in shallower water, Maiolie said.

Biologists also walked suspected spawning sites, turning over rocks in search of eggs. And drove the shoreline looking for gatherings of birds that might be feasting on fish eggs. But the latter efforts have proven fruitless.

“We believed it was worth a try,” the IDFG’s Russ Kiefer told the Technical Management Team last week.

The U.S. Army Corps of Engineers regulates the level of Lake Pend Oreille with the operation of Albeni Falls Dam. On Oct. 7, discharges increased from about 13,000 cubic feet per second to 28,000 cfs within about two days. The project is being operated to draft 11 feet to elevation 2, 051 feet above sea level, by mid-November. By Halloween morning it had dropped to 2053.7.

The large and predatory lake trout feed on kokanee salmon, the favored Lake Pend Oreille fish species, and are considered a key factor in the kokanee population’s steep decline. The also prey on bull trout, which are listed as threatened under the Endangered Species Act.

Recent population surveys indicate that the lake trout population is continuing rapid growth. The population data is gained via IDFG trap netting efforts, commercial netting and sport catches.

A truer assessment of the drawdown’s effects on the lake trout population will come from population surveys five years from now and beyond. Lake trout begin showing up in catches at about 5 years old when they’ve reached about 16 inches in length. A noticeable dip in the population from the 2006 brood year could be a sign that the post-spawning drawdown was a success.