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Flathead Lake trout populations change in response to restoration efforts

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Flathead Lake teems with fish in today’s environment, and the most abundant trout species aren’t the ones that historically belong there but that’s changing. 

Humans introduced lake trout, currently the dominant trout species in Flathead Lake, about 100 years ago. Lake trout eat other fish, including the native cutthroat and bull trout that have been part of the lake’s ecosystem since the last ice age. Over time, lake trout began to drastically drive down the population of native trout in the lake to what Confederated Salish and Kootenai Tribal biologist Barry Hanson calls “dangerously low levels.”

After analyzing of the factors influencing native trout die-off, CSKT and Montana Fish Wildlife and Parks determined that it was the lake trout killing native trout. 

“The only way to restore native trout is to reduce predation and let them recover,” Hanson said. CSKT officials made a plan to restore native trout. The goal of the plan was to reduce the number of lake trout by 75 percent. 

Native trout are culturally relevant to the Confederated Salish and Kootenai Tribes and are important to keeping the lake’s ecosystem healthy. While the total population of lake trout in Flathead Lake has not declined significantly yet, Hanson says data shows the efforts are gradually working.

CSKT and FWP raised the limit of fish one angler could catch to 100 lake trout per day. The tribes started the semi-annual Mack Days fishing competitions, where participants are eligible for rewards based on the lake trout they catch. In 2014, CSKT implemented the final phase of the plan: gillnetting to catch the non-native trout. 

There isn’t a strict timeline associated with the native trout restoration plan. Hanson said the intermediary goals are to strive to increase the harvest every year until they meet their goal of harvesting 143,000 lake trout each year. Hanson said in recent years, about 110,000 lake trout have been harvested annually. 

According to Hanson, the slow-and-steady approach is intended to ease concerns among the public and prevent a shock to the ecosystem. “We wanted to do a gradual change over a long term,” he said. 

Because the goal of the project is a 75 percent reduction in the number of lake trout, rather than total elimination of the species, the project will have to continue forever and that’s because it’s unrealistic to try to eliminate lake trout altogether, Hanson said. Lake trout thrive in Flathead Lake where they have a habitat that keeps them healthy with few threats.

“We accept that they’re going to be there,” Hanson said. 

The fact that the restoration project has to go on in perpetuity means CSKT needed to find a way to make the ongoing project sustainable. In 2017, the tribe established a corporation called Native Fish Keepers to process and sell the fish harvested from the restoration effort. The proceeds from those sales go back to funding the restoration. 

Hanson said he considers the project a success to date, but revenue from the project only covers about 20 percent of the costs of running the program. He said he hopes it will become more profitable as time goes on. 

While the total fish population in the lake hasn’t dropped dramatically since the restoration efforts started, there are some promising changes. For one, the majority of the fish in the lake are younger and smaller than they were when the project began and that’s because the fish have aggressively reproduced in recent years. Hanson explains that this phenomenon is related to the amount of food each fish has available to eat. 

At their peak population, there were so many lake trout in Flathead Lake that there was just enough food for each fish but no excess. As a result, the fish started growing more slowly and reproducing later in life in order to save the available food for living fish. 

When anglers and CSKT started harvesting lake trout aggressively, more food and space became available than the lake trout needed to survive. In response they started growing more quickly, reproducing at younger ages and laying more eggs. This is the way the lake trout population compensated for the reduced population. However, there’s a limit to how far the fish can adapt. Lake trout need to reach maturity to reproduce, and there’s a limit to how many eggs they can lay. 

Hanson said that once anglers “fish through the compensation” and continue reducing the number of lake trout, the total number of lake trout will drop. This phenomenon can be observed in the results of recent Mack Days competition. The Spring 2019 competition had a record-high fish harvest; however, the fish being caught during Mack Days aren’t very big. 

This fall there were three entries into the “smallest catch” category, but no one has entered a particularly large fish. The smallest to date was about five inches. This indicates that anglers and nets have caught the larger, older fish and most lake trout that remain are young and small. 

“For now it will get harder to catch big fish and easier to catch little fish,” Hanson said. 

Hanson predicts it will take a few years to reach the goal of harvesting 143,000 lake trout per year, but, until then, populations will continue to decline. At least 10 years from now, Hanson expects the target of 75 percent reduction to be achieved. 

Anglers who worry the restoration project will eliminate their opportunities for sport will always have the option to catch lake trout, though as the project continues there will be fewer fish available. The hotspots for fishing in the lake will most likely keep providing anglers with fish.

Anglers who have identified good fishing spots, where fish congregate because the habitat is welcoming, won’t see much change in the number of fish at their favorite spots. While it’s clear that lake trout populations are changing, the real goal of the project is to save the native trout. 

A lake trout can eat a native trout roughly half its own size. That means that as anglers catch the big lake trout the native trout can grow larger. The larger the native trout get, compared to the lake trout, the better their chances of survival. 

Hanson said he doesn’t have any hard data that indicates a rebound in the native trout population but he expects it’s in the works. Repopulation will take time, he says, and it’s still early in the effort. “We’ve picked this steady course that we think makes most sense biologically and for users, and we think it is starting to pay off,” Hanson said. “We’re confident that it will over time.”

According to event organizer Cindy Bras-Benson, this years Mack Days has been pretty typical. The biggest excitement came when an angler caught a struggling bobcat in his net and brought it to shore. Warm weather early in the competition brought in a lot of fish, but cold temperatures lately have deterred anglers. This season saw one particularly windy day where no one caught a single fish, and Bras-Benson said that’s rare and it hadn’t happened in several years. 

The week of Oct. 11 saw the largest harvest of the tournament so far. A fish tagged with a value of $500 is the highest prize the competition has seen so far. Nikko Alexander caught that fish on his first time fishing on Flathead Lake. “He caught 20 lake trout and one was a $500 fish,” Bras-Benson said. 

So far anglers have caught 14,108 fish during the competition. “We just want to see people continue to enter and help us out, reducing these lake trout so our population of native fish can expand,” Bras-Benson said. The competition ends on Nov. 10.

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