Yellowstone Lake: Answers to Your Questions


Yellowstone cutts vs. lake trout:

Get the Facts


Trout Unlimited strongly supports the ef- forts of National Park Service, U.S. Geological Survey and others to recover the native Yellowstone Cutthroat Trout (YCT) popula- tion associated with Yellowstone Lake and the Upper Yellowstone River.

As part of that conservation mission, TU strongly supports efforts to suppress the nonnative lake trout population in Yel- lowstone Lake. Opponents of the lake trout suppression efforts have made a number of claims that warrant a response. Here are some frequently asked questions, along with the facts:

Why do Yellowstone cutthroat trout need to be protected?

Yellowstone cutthroat in Yellowstone Lake are the largest genetically pure population of the subspecies on Earth; if they are not restored, the likelihood of listing under the ESA and more restrictive regulations in- creases substantially. YCTs serve a critical role in the lake ecosystem, providing an important food source for bear, osprey, eagles, and many other species. (Lake trout, by contrast, live primarily in deep water, only entering the shallower parts of the Lake to feed on cutthroats or to spawn. They rarely, if ever, ascend the tributaries. Thus, they do not serve as a food source for other predator species.) Moreover, YCTs have important human values: The YCT population has been a historic draw for Park visitation and an econom- ic driver for tourism and recreation.

So why are Yellowstone lake trout a problem?

Since the discovery of lake trout in Yellowstone Lake in 1994, the once abundant Yellowstone cutthroat population has declined dramatically to less than 10 percent of their historic numbers. Of all the possible factors leading to this decline, biologists and fisheries managers have overwhelmingly pointed to one as the main culprit—predation by lake trout. Suppression of lake trout has been called for by an independent, expert scientific panel that was first convened in 1995 and has reviewed the matter several times, most recently in 2014, when the panel called for a continuation of suppression efforts.

Couldn’t the cutthroat decline be explained by other factors?

There is no scientific evidence suggesting that whirling disease, drought, fire or some other cause has re- sulted in the drastic drop in Yellowstone cutts in Yellowstone Lake. While these causes have had some impact, all studies point to lake trout predation as the driving factor in the decline.

Haven’t lake trout been in Yellowstone Lake for more than a century?

The oldest lake trout in the Lake has been found to be only 21 years old, half of their typical life span. This indicates the population established itself around 1990, which is corroborated by the fact that the first verified lake trout catch was in 1994. In addition, a scientific study of these first catches indicates that these lake trout spent their early years in a different water body, most likely Lewis Lake.

But is there proof that they’re eating cutthroats?

Extensive studies in the 1990s revealed that fish comprised 95 percent of the diet of age 4-plus lake trout in Yellowstone Lake, and most of the consumed fish were Yellowstone cutts. Prior to the introduc- tion of lake trout to Yellowstone Lake, there were no fish predators eating YCTs; the drastic reduction in Yellowstone cutts since the lake trout population became established is irrefutable.

Why can’t the lake trout and cutthroats coexist? They
do in other Park lakes

That’s true, but fish biologists say that’s because those lakes have more varied fish populations. In Heart and Jackson lakes, which also have non-native lake trout, the presence of many more fish species for lake trout to eat has likely moderated their impact on Yellowstone cutts in those lakes. In Yellowstone Lake, essentially the only fish in significant numbers for lake trout to eat are YCTs.

Why should the Park Service be spending millions on lake trout suppression when other services are being curtailed? Isn’t the effort too expensive?
The lake trout suppression effort costs about $2 million/year. In contrast, the YCT fishery was bringing in an estimated $30 million in economic activity in the early 1990s when populations were still robust. From an economic perspective, it makes sense to save the YCT fishery.

Is the lake trout a “bad fish,” then?

No. Many anglers seek out opportunities to catch lake trout, a popular game fish in their native waters of the Upper Midwest. But in the Intermountain West, several states (including Wyoming, Idaho and Mon- tana) are trying to suppress them because of the damage they cause to native fisheries. And in the West (most notably Yellowstone Lake), native cutthroat trout provide better opportunities for anglers and far greater economic benefit for local communities.

Have the lake trout removal operations been successful?

The suppression efforts are making significant progress, with improved YCT numbers and a clear trend of declining lake trout numbers. While lake trout in Yellowstone Lake cannot be completely eradicated, the Scientific Review Panel believes that if present culling efforts continue, YCTs can rebound to the more robust population levels recorded in the late 1980s and early 1990s. This would be an important victory for YCT conservation. Now is the time to redouble our YCT restoration efforts—not call them off.

Culled lake trout: heavy feeder

For more information, contact:

David Sweet, Wyoming Trout Unlimited,, (307) 527-9959

Scott Christy, Wyoming Trout Unlimited,,  (307)-332-7700 x. 12 



said on Wednesday, May 21st, 2014

I think the term 'invasive species' is overused.

Lake Trout, in my understanding, were intentionally introduced into Yellowstone Lake by the Wyoming DNR, likewise with Heart, Lewis, and Jackson Lakes.

I don't have an issue with the effort, although perhaps it might be more cost effective to introduce another forage species, such as Wyoming native chub or sucker, into the lake instead of removing the Lake Trout; there is almost zero chance of getting all of the Lake Trout, so the most likely scenario is perpetual culling...

I know introducing any species into a body of water in which they are not already found is a risk; but the barn door is already open here; perhaps biological sciences can help balance the ecosystem with another forage species...




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