Lake Pend Oreille, located in northern Idaho, is the state’s largest lake and home to a diverse array of native fish, including bull trout and westslope cutthroat trout. And its kokanee fishery, besides being a popular sport fish, is a critical food source for a variety of other fish, including trophy rainbow trout. Pend Oreille researchers have linked fast rainbow trout growth rates to high juvenile kokanee abundance.
One of the biggest challenges to sustaining the lake’s fisheries has been predation. In the late 1990s, the number of non-native lake trout, which prey on kokanee, exploded, nearly decimating the kokanee fishery.
At its April meeting, Regional Fishery Manager Andy Dux and Principal Fishery Research Biologist Matt Corsi of Idaho Department of Fish and Game briefed the Council’s fish and wildlife committee on the progress of the Council-funded resident fish program to suppress predatory lake trout and walleye in Lake Pend Oreille.
The Idaho Fish and Game’s lake trout suppression program, funded by the Council, Bonneville Power Administration, and Avista, has been an encouraging success story for the kokanee population. Through a combination of gill nets, trap nets, and paying anglers to catch them, about 240,000 lake trout have been removed from the lake.
The impact has been a dramatic increase in kokanee numbers, as well as improved numbers of rainbow trout, bull trout, and cutthroat trout.
Balancing predator and prey populations to sustainable levels will be an ongoing challenge, as new problems are emerging from predation by walleye and northern pike. Walleye are of particular concern because they've been increasing most rapidly and the lake offers an abundance of suitable habitat.
“We’re being proactive with walleye, and hopefully we’re getting ahead of them before they cause a predation problem to any portion of the Pend Oreille food web,” notes Corsi. “We’re going to take the same science-based approach we did with lake trout to understand both the threats and the management solutions.”
To address the walleye threat, in 2019 Idaho Fish and Game contracted a commercial netting company to remove 2,684 fish and implemented a reward program to encourage anglers that removed another 1,645 fish.
Overall, results suggest that the suppression program has made a big difference in restoring the lake’s world class fisheries.
“Effectively managing predation has allowed the recreational fishery in Lake Pend Oreille to rebound,” said Dux. “Fishing is better now than it has been in over 25 years.”
Summing up, Fish and Wildlife Committee Chair Jeff Allen observed, “We know when kokanee do well, all the fish do well.”