The official crackdown on invasive northern pike in the Pend Oreille River behind Box Canyon is in its last stages for this season.
A late-April survey indicated gillnets deployed by the Kalispel Tribe and Washington Fish and Wildlife Department were shy of a goal to remove 5,700 pike this spring from the 55-mile stretch of river downstream from Newport.
Based on several years of research, the state announced this winter a plan to crop the burgeoning pike by 87 percent. Officials said the non-native pike were overpopulating to the point they were showing a trend to stunting. Meanwhile, the apex predator posed a threat to native fisheries.
Fisheries professionals said they were especially concerned about overpopulated pike looking for new homes down the Columbia where they might threaten expensive efforts to restore endangered salmon and steelhead runs.
During the first gillnet removal phase from late March through April 22, workers setting 12-20 nets a day killed a total of 4,552 northern pike, said Jason Connor, the tribe’s fisheries project manager. The initial goal was set at 5,700.
“The catch rate dropped off quite a bit at the end of phase 1 partly because the river water levels dropped at that time and we couldn’t get the nets in the best spots, and partly because there were a lot fewer pike out there by that time,” he said.
The gillnets first were set where research indicated the most pike would be heading into spawning areas. As catch numbers dropped, the nets were set in marginal areas, he said.
On April 23-26, the workers put out 20 nets a day in random patterns from Box Canyon Dam upstream to Pioneer Park to index pike abundance throughout the reservoir.
A similar effort in 2011 calculated 13.2 northern pike per net in the southern half of the reservoir, the most productive stretch.
This year the ratio was 2.9.
He said the workers caught 131 northern pike in a total of 60 net sets during the three-day full-reservoir index survey.
“That shows we’ve been successful in reducing pike numbers, but we need to go further,” Connor said.
To reach the goal of cropping the pike by 87 percent, biologists say they need to keep fishing until the population index nets average less than 1.73 pike per net.
“In the northern half of the reservoir the goal is to be less than 0.5 (fish per net) and we were at 0.8, so we’re pretty close there,” Connor said.
The size data have not been compiled yet, but Connor said most of the northern pike seemed to be in the 23- to 24-inch range, weighing 3-3.5 pounds. That’s a sign the average size has declined in recent years, which is an indicator of overpopulation, he said.
During the entire pike reduction phase, the nets caught 201 largemouth bass and nine smallmouth bass, Connor said, noting the nets are geared to avoid as many bass as possible.
On April 27, workers began putting out the pike reduction gillnets again and tending them daily.
“We will continue until we see that 87 percent reduction at every site we go to or until reservoir conditions are no longer conducive to gillnetting,” Connor said.
Netting will be weekdays only starting this week to avoid interfering with fishermen who will be coming out as weather gets nicer, he said.
By mid- to late-June, the river’s water levels will drop making the backwater sloughs inaccessible because of lower water and heavy vegetation growth, he said. “In summer, the water in the sloughs gets too warm for the pike, so they move out into the main river channel, where they tend to move around a lot,” he said.
Meantime, Box Canyon Reservoir waters continue to rapidly change in flow and elevation.
“We’re about 5 feet higher than at this same time last year because of the way rain on snow is coming off the mountains,” Connor said.
“They’re at full spill over Albeni Falls Dam.”
Average water temperatures last week were 47 degrees in the main channel and up to 57 degrees in some of the sloughs, he said.