Elimination of lake trout from Yellowstone Lake increasingly successful

Evidence is the onslaught of these ecologically useless fish is ending-

We haven’t discussed the status of the illegally introduced lake trout in Yellowstone Lake for two years now, but the continuing evidence for their decline is good.

The dawn to dusk, 6-days-a-week effort, gillnetting with five boats is catching fewer lake trout each year. Wildlife that eat the native Yellowstone cutthroat trout seem to be increasing. The largest netted catch was 300,000 back in 2012. Since then, given about the same amount of effort, the total number of lake trout netted is slowly declining each year. More importantly, the number of mackinaw caught per 100 meters of net per night (catch per unit of effort or CPUE) has been more steadily declining. CPUE has gone from eight fish per 100 meters of net to five fish.

Yellowstone Lake anglers are required to keep or kill all lake trout caught. It is estimated anglers are responsible for about 10 per cent of the total annual removal. It is the $2-million a year spent on the netting program then that is making the difference. The Park Service believes these trout that almost destroyed the lake’s ecosystem can never be entirely eliminated, but their numbers can be driven so low that the pre-existing population of Yellowstone cutts can be restored. Hopefully, the genetic variation will not be less than before in a restored population of the native trout.

Lake trout are a disaster because they rarely come to the surface. While they are voracious eaters of cutthroat trout, nothing eats the lake trout. Osprey, eagles, pelicans, otter, black and grizzly bears are the most prominent animals that eat the cutthroat which are frequently taken near the surface where they feed, and in the creeks that supply the lake, up which they run and spawn.

Effects of the lake trout invasion were not only on the animals mentioned above, but others too, such as the elk of Yellowstone whose number declined indirectly due to fewer cutthroat trout in the lake. Grizzly bears that had relied on the trout turned in part to the Park’s elk for their sustenance.

The illegal introduction of mackinaw to Yellowstone Lake probably happened in the 1980s. Chemical analysis of the introduced trout indicate that they were transported from a nearby lake, i.e., Shoshone Lake or Lewis Lake. These two were originally barren of trout, but had mackinaw stocked in them in the 1890s. The first officially recorded lake trout caught from Yellowstone Lake came a century later — 1994. The number of native cutthroat trout in Yellowstone Lake then quickly declined.






  1. rork Avatar

    Thanks. I was hoping for more dramatic decline based on reports from last year. Also, I’m still hoping that rebound in cuts might help decrease lake trout, by a little predation and competition for food, but those effects might be small. I found it interesting that the gill netters send the dead fish to the bottom of the lake rather than selling them. Loss of possible money for lake trout removal effort but I get it.
    When transporting, cooking, and eating trout in wilderness near Yellowstone, I’m always a bit jittery. Freshly overturned boulders in the area make my symptoms worse.

  2. Ralph Maughan Avatar
    Ralph Maughan

    Hopefully, continued technical progress in locating and tracking these deep water trout will yield increasing success.

  3. Ralph Maughan Avatar
    Ralph Maughan

    The excerpt below comes from a technical report published in 2012. That was before the recent trend toward much greater success netting the lake trout. I wish I could find the most recent data on the number of yellowstone cutthroat trout landed per hour by anglers. If anyone can, I would appreciate you posting it.

    “Scientific evidence in the form of creel surveys conducted by the U.S. Fish and Wildlife Service and the National Park Service reveal that for the 15 years prior to the discovery of lake trout, the average landing rate by anglers on Yellowstone Lake was over one and a half cutthroat trout per hour of fishing (Gresswell et al. 1994). Subsequently, the landing rate for anglers steadily declined to less than one half of a fish per hour of fishing in 2006 (Koel et al. 2012). Despite the very substantial lake trout suppression program in recent years, the landing rate of cutthroat trout has not exceeded one fish per hour since 2001 (Koel et al. 2012).”

  4. Kathleen Avatar

    If one is willing to acknowledge that even invasive species are sentient animals, situations like this never result in an unqualified “win.” Lake trout are not useless or “garbage fish” (as I’ve heard undesirable fish species called) in their own habitat, gill netting is cruel, and it’s tragic that this sort of thing happens as frequently as it does. Yet I understand as well as any (and better than many, having waged my own prolonged battle against invasive weeds) the problem with nonnative plants and animals wreaking havoc in ecosystems. Thing is, these fish didn’t stick their thumbs out (ha ha, picture it!) and hitch rides to their new habitat…yet THEY are the ones reviled for being there and eradicated with pleasure, and that isn’t fair. We should at least acknowledge that.

    And while I’m at it, I’ve frequently heard the term “bucket biologist” used for the law-breakers who commit illegal aquatic introductions, a term I find disgusting. It lends an air of respectability to what *should* be considered eco-terrorism. If animal rights activists can be prosecuted under terrorism laws for attempting to reveal cruelty and save animals’ lives, someone who destroys an entire ecosystem should, too. I realize they’re seldom caught–at the very least, they should publicly called out for what they are–eco-terrorists, and not be given a pass with a benign term like ‘bucket biologist.’

    Yes, it’s critical to get a handle on ecosystems devastated by nonnatives who then set off a cascade of negative effects, but don’t blame the transplanted animals. Asian carp didn’t swim here, right? Invasive animals have been exploited by humans–as pets/exotics (Burmese pythons in the Everglades) or for their fur (nutria) or introduced for hunting/fishing opportunities–whatever. The humans should get the blame but, as always, the animals pay the price.

    1. Ida Lupine Avatar
      Ida Lupine


      I’m glad that the fish are being removed without poisoning, even though it takes more time that way. Some of our wonderful snakes eat lots of non-native invasive fish too I have been reading.

    2. Jay Avatar

      I don’t see anybody dancing on their graves–I see people encouraged with positive news that an entire ecosystem is being restored with the removal of an invasive species.

    3. rork Avatar

      In some high lakes in U.S. western mountains, the fisheries biologists were the eco-terrorists. They’d introduce cutthroat or even brook trout, in “unused” cirque lakes. I’ve fished California golden trout in Montana even. It’s nice to have fishing and for food, but it might have been a wonder to get to study what kind of things were going on without the fish. Small fish-less lakes and streams can have fantastic aquatic insect hatches, that in turn feed other things like dragonflies, frogs, birds. I’m rather amazed the brookies haven’t created more havoc by invading surrounding streams, but maybe the cuts or bows out-compete them if there’s appropriate spawning habitat, and it’s only in high lakes where brook trout can win (they are char, like the lake trout, and can spawn in stiller water if they must). In MI, brown trout, rainbow trout, and brook trout can coexist. In some of our rivers all three might be deemed invaders, since grayling were historically dominant. Historically the grayling could beat off the brook trout invasion in our coldest rivers (Au Sable, Manistee), when it was just the two of them fighting it out, and less humans fishing.

  5. monty Avatar

    Wow! More good news!!!!!!!!!!!!!!!!!

  6. Steve Avatar

    I never see it mentioned, but a theory that I tend to believe could be true regarding the introduction of lake trout is that during the huge fires of 1988, they used a lot of aircraft to scoop and dump water on the fires. Those aircraft scooped water from shoshone and lewis and dumped on fires along yellowstone lakes’ shores, and some minnows made the trip. Far-fetched (?), but the timing of when they showed up fits perfectly.

    1. Ralph Maughan Avatar
      Ralph Maughan


      I have argued this possibility in the past, but I didn’t mention it in this post — mainly because it was not well received previously.


Dr. Ralph Maughan is professor emeritus of political science at Idaho State University. He was a Western Watersheds Project Board Member off and on for many years, and was also its President for several years. For a long time he produced Ralph Maughan’s Wolf Report. He was a founder of the Greater Yellowstone Coalition. He and Jackie Johnson Maughan wrote three editions of “Hiking Idaho.” He also wrote “Beyond the Tetons” and “Backpacking Wyoming’s Teton and Washakie Wilderness.” He created and is the administrator of The Wildlife News.

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Ralph Maughan