Yellowstone Lake Cutthroat Trout Threatened by Non-native Lake Trout


80,000 non-native lake trout removed from Yellowstone Lake

Fisheries biologist likens removal of non-native lake trout from Yellowstone Lake to “weed control”

Yellowstone Lake is home to the largest remaining population of Yellowstone cutthroat trout in North America. But since non-native lake trout were discovered in Yellowstone Lake by an angler in 1994, the famous cutthroat population has been threatened.

Lake trout aren’t welcome in the lake. Fisheries personnel have removed the fish in large numbers. To date, more than 80,000 lake trout have been removed.

The potential damage a lake trout population can cause cutthroat is enormous.

For starters, a lake trout lives through two or three generations of a cutthroat. A lake trout may live for 25-40 years, a cutthroat, maybe 10 years.

“Lake trout are so long-lived,” says Pat Bigelow, fisheries biologist. “A seven-year-old cutthroat is sort of an old fish. If you have seven years of serious impact on the juveniles coming up, you could lose your whole population.”

A big lake trout taken from Yellowstone Lake weighed 21.5 pounds. A big cutthroat in the lake – maybe even a trophy catch – would weigh about five pounds.

As soon as a lake trout reaches four years old, it begins eating cutthroats, which make up half of their diet. A couple years later, it eats cutthroats almost exclusively. Typically, a mature lake trout will eat 50 cutthroats a year. The non-native lake trout are not only eating several cutthroats a year, but they compete with the native fish for the same food sources. Lake and cutthroat trout both feed on leaches, amphipods, and lake midges.

A Life Cycle for Domination

Lake trout are a reproductive bunch, spawning eight to 10 years in a row, each time yielding 1,000 eggs per kilogram of body weight. This means a 20-pound lake trout could produce 10,000 eggs. If just one percent of those eggs survive, you’re talking 100 new lake trout born to a single fish in one year. On the other hand, a cutthroat may spawn only once or twice during its lifetime.

It doesn’t take a calculator to conclude that lake trout will do serious damage in a short amount of time if left unchecked at Yellowstone Lake.

A panel of fisheries experts that met in 1995 to assess the lake trout’s presence and likely impacts on Yellowstone cutthroat population estimated that, with effective suppression of lake trout numbers, the cutthroat population decline might be held to 10- to 20 percent of present levels. Without some control of lake trout, the experts predicted the cutthroat population would be reduced by 70 percent in 100 years.

Other Impacts

The cutthroat population is valued ecologically, economically and socially. Cutthroat trout live and spawn in shallow streams and waters, providing prey for at least 42 species of birds and mammals. Grizzly bears, otters, eagles, white pelicans and osprey are just a handful of the animals that stand to lose a valuable food source if the Yellowstone Lake population is diminished.

Furthermore, the cutthroat trout in the lake help generate $36 million in revenues resulting from the world-class sport fishing found in Yellowstone and surrounding communities. Anglers come from all over the world to fish for these native wild fish.

Netting to the Rescue

Since 1995, fisheries staff in Yellowstone have been netting lake trout. Some fisheries biologists have called the effort a “forever project.”

In 2001, Yellowstone received a new gill-netting boat, which significantly aided fisheries biologists in their netting efforts. The boat was designed as a scaled-down version of commercial gill netters used on the Great Lakes. The boat, which is 32 feet long and 14 feet wide, has a net lifter designed for pulling nets off the bottom of the lake.

Before the boat’s arrival, fisheries biologists had to pull in the large nets that were full of lake trout varying in size from a half a pound to 20 pounds. It was grueling work.

Last year, 18,000 were netted – five thousand more than the previous year.

“We did really well last year,” says Bigelow. “We increased our effort and as a result removal was up 40% over the year before.”

Trying to ‘hit ’em hard’ During Spawning

Most of the lake trout currently being netted are two or three years old. These immature lake trout are found at depths of 150-250 feet. Netting is also being done in some 50-foot depth areas of the lake, where crews are able to net some large, adult lake trout.

Medium-sized lake trout, however, are difficult to net because they share many of the same waters as cutthroat trout. To net this age group of lake trout, fisheries biologists have located some key spawning areas in the lake and during the lake trout’s spawning season, have been able to net large numbers of medium-sized lake trout.

“When lake trout reach five or six years old, they become sexually active,” says Bigelow. “We’re looking to net them during times when they’re segregated from the cutthroats, which means catching them during the spawning window.”

Bigelow says an additional spawning area near West Thumb Geyser Basin was located last year and resulted in some increased removals of mature lake trout. During recent months, fisheries personnel have been busy trying to determine additional spawning areas via mapping, says Bigelow. The goal is to find additional spawning areas this year during netting efforts so more of the medium-sized lake trout can be removed from the lake.

Spawning for lake trout begins at the end of August and runs through September.

Anglers Help

In recent years, Yellowstone Park has issued a release inviting anglers to help control the lake trout population in Yellowstone Lake by allowing anglers to fish spawning areas of the lake during September and October. There are no creel limits.

As lake trout mature, they become more predacious, Bigelow says, and they intermingle in the shallow water with the cutthroats. They move less, and are harder to catch in the gill nets.

“They have to swim into the nets for us to catch them,” explains Bigelow.

Bigelow says fisheries biologists are having a difficult time catching these older lake trout, but that anglers are doing quite well catching lake trout in this age group.

Anglers are urged to fill out response cards after fishing the lake to report their catches. This helps fisheries biologists better monitor catch rates.

A “Forever Project”

Bigelow says it’s not likely that the last lake trout will ever be caught in Yellowstone Lake. A more realistic goal is to get ahead of the problem, she says.

She compares the lake trout removal effort to weed control. The lake trout problem isn’t going to go away, but with great sustained efforts fisheries biologists might be able to prevent it from taking over the lake completely.

Like weeds in a yard, the unwelcome lake trout that’s populating the famous Yellowstone cutthroat’s home might be reduced in numbers. Its damage should be minimized as a result of continued netting and removal of lake trout, says Bigelow.

Comment Feed

11 Responses

  1. My wife and I just returned from Yellowstone, and we towed our boat there, so we could fish in the lake. In my youth my family took a trip (in the late 60s) to Yellowstone with our boat, where we enjoyed catching our limit, and feasting on the only cutthroat that I had ever seen with purple guts and pink meat.

    When researching this recent trip I was saddened to hear of the current problem with Lake Trout. We fished for two days in the lake, and had fun catching several very large (3 to 4lb) cutthroats. They were beautiful fish and fun to catch, and of course releasing them immediately. However we never caught one Lake Trout that first two days. One afternoon we drove to Grants Village, where we asked a Park Ranger about the Lake Trout. He referred us to another worker who has ongoing success catching the Lake Trout.

    We learned that we were fishing in the wrong area of the lake to catch Lake Trout. We also did not have the correct lures. We went to the nearest store in Grants Village, but they did not have the right lures either. We fished in the suggested locations the next day, and I immediately caught a lake trout (about 13 inches). I figured we would catch several, and I would only keep a few bigger ones. I slit the Lake trout through the lungs, and tossed it in the lake. It was the last one we caught! (Bummer!)

    My suggestion is for the rangers to make information (unavoidable) regarding where and when the best locations and time are to catch Lake Trout. Also provide information on depth (we were on the bottom), and how to catch them. One other thing is to make available at multiple locations where an angler can buy the lures needed to catch these lake trout.

    You might even give a pamphlet with this information to every angler when they purchase a fishing permit, along with the other information which is already given.

    One question… What is done with all the fish pulled up in the gill nets?

    Thank you, Terry

    Terry HarrisOctober 4, 2011 @ 2:42 pm
  2. I agree, Terry!

    Come on Park Service! Make a map of the lake available showing the spawning grounds. Give best tackle reccomendations. Advertise this info in Billings, Bozeman, Cody, Jackson and Idaho Falls to spark interest. Post some big fish pictures.

    Lets get sportsmen involved in this project!

    I really miss the Cuts in the Thourofare. I would love to put the hurt on those lakers.

    Mike YorgasonNovember 2, 2011 @ 12:38 pm
  3. Im a student and really concerned about these trout taking over. SO I hope they can get to a point where there are more Cutthroat than the LAKE TROUT!

  4. I agree James, bu Ive read slot, and they say it’s a forever project, so well see!!!!!

  5. I disagree I think they will have it under control soon!!!!!!

  6. interesting to read the prediction that cutthroats could be reduced 70% in 100 years.From our experience fishing the Upper Yellowstone and Thorofare the last 35 years it seems like the number of spawning cutthroats have already been reduced 85 or 90%.
    Keep up the good work with the nets guys–‘hope you can increase the effort.


    forest stesrnsFebruary 10, 2012 @ 2:54 pm
  7. u be needing more infromation on lake trout in yellow stone lake!!!!!!!

  8. I’m going fishing next summer during the 4th and would love to get some info on where to fish for lake trout. I have capabilities to fish any depth so its just a matter of where to fish in the lake. Please provide any pointers.


  9. Grew up fishing the “jelly”stone opener every 15th of July and in the 80’s our arms would be so tired at the end of a day from catching and releasing 30 to 40 cuts(each). Now days most of our family does not attend as the cut throat population has drastically fallen. Two fish was all we got last year. We used to be able to spot dozens of cuts while wading the river, but they just aren’t there anymore. The waters seem to be getting warmer as well and I wonder if this is doing harm to the cuts? 20 years ago if you had a hole in your waders you would have to get out every couple of hours and thaw out, and last year we saw people in shorts during the opener.

    I agree with most of the threads above. The lake trout need to go! I plan on towing my boat to the lake many times this year. I know my actions alone will not even put a dent in the lake trout population, but I will have fun trying. All the help we can get from the parks dept would be greatly appreciated. If we plan to target just the Lake trout, can we go after them with lead weights and lures? What about reducing the cost in licenses and permits? How about hosting and advertising a fishing derby during the spawn when they are in the shallows? I think you would find that hosting such an event would pay for itself (plus increase money for different methods of removing the Lakers) in no time and would greatly build into a huge annual event. Plus, that would be one hell of a fish fry at the end.

    Nate GilbertMarch 15, 2012 @ 1:10 am
  10. I did well catching lake trout. The best techniques uses leadcore line or downriggers, to get the lure at least 9 feet down consistently while trolling. I used a thomas boyant in gold/red to catch 7 in two hours at Stevenson Island. I would expect a good 5″ rapala in a cutthroat trout pattern would be good for 10 to 30 pounders. You must bring your own leadcore rod, reel, and line as no one sells it up there. I also use a battery operated gps depth finder, for depth and speed. If you rent a boat in Bridge Bay you cannot go very far past Stevenson Island and you must have two persons to rent a boat. Based on some of the trout tracking data I saw, the area from Dot islad to west thumb have alot of lake trout activity. Next, I am planning to float tube at a stream inlet with a tan or tan and red streamer with heavy sink flyline. The laketrout I caught up to 7 lbs had been eating brown leaches (looked like rubber bands) or pink scud(small shrimp). In the fall the lakers can be hard to catch, unless you find a spawning area – then it can be every cast.

    Greg -flyandfishMay 3, 2012 @ 9:54 pm

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