How does a fish cause the diminishing of the Elk herd in Yellowstone?
When we visited Yellowstone Park in 2000 there were elk everywhere. These big beautiful ungulates abounded to the point of us saying “Elk?” who cares. When we returned in 2012 the herd was greatly diminished. “Wolves” is the cry from ranchers and the uninformed. Yes, wolves do prey on elk, but they take only the old and sick and actually improve the health of the herd overall. No, the reduction of the Elk herd is not the fault of the wolf. It is much more complex and mysterious.
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This story begins with a fish. The Lake Trout was accidently introduced into Lewis Lake sometime in the 60’s. No one knows how it got into Lake Yellowstone. Lake trout are one of the largest members of the trout family, some running as long as 36” and weighing up to 15 pounds and they are delicious! One good sized Lake Trout can feed a family of five (it was delicious). They are fun to catch and as reported, to eat as well. Lake Trout are however, the villains in my tale.
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Lake Trout lie in the depths of Yellowstone Lake and devour Cutthroat Trout which live at the surface. The Lake Trout is a ferocious predatory fish. It eats the Cutthroat faster than the smaller fish can multiply. Because the Lake Trout lives in the depths of the lake it is inaccessible as a viable food source for the animals that prey on the Cutthroat. The Cutthroat is indigenous to Yellowstone - the Lake Trout is not. Okay you may be saying; the big fish eats the smaller fish…that’s nature.
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Yes, it is, except the Cutthroat Trout also is prey for up to eighty-one animal and bird species in the park. Because it lives near the surface of the lake and breeds in small creeks and rivers that feed into Lake Yellowstone, it is easy to catch and eat. The Cutthroat Trout is a key food source for bear, otter, badger, bald eagle and, osprey just to mention a few.
Enter the Grizzly Bear. Our favorite bear to watch is the Grizzly and they abound in Yellowstone National park. One of the key prey items on the Grizzly’s menu was the Cutthroat Trout. As the fish is disappearing and no longer a source of protein and fat for our bear it needs to find another source to replace the now rare Cutthroat Trout.
Grizzly bears have a range to hunt in, they also do not go out of that range to find food. Instead they change their diet and adapt to new food sources. With the Cutthroat Trout now almost on the endangered species list in Yellowstone the bears are finding new food sources. In a study conducted by the National Park Service it has been discovered that the Grizzly Bear has changed from fish to Elk.
This study found that the bears are not taking the adult elk like the wolf does, they are taking the new born. In the last ten years, there has been such a huge drop in the number of surviving infants that spotting Elk in the park is now a treat.
What’s being done?
The park service has started waging war on the Lake Trout. This war includes professional fishing boats taking millions of tons of Lake Trout out of the lake. It also mandates killing any Lake Trout caught; no catch and release for these interlopers. The goal is to reduce the Lake trout population and to give the Cutthroat a chance to recover. So far it’s been a losing battle.
Yellowstone is constantly changing. Fires, new thermal eruptions and animal populations are constantly renewing the park and changing its landscape. As the Grizzly impacts the Elk we have yet to see how a diminished Elk population will impact the park.
The “Take Away” here is a word of caution. Even fish have drastic and unintended consequences, please don’t bring any creature into a park and let it go. People put a great hunting fish into a lake. Maybe they were thinking about how much better catching a huge lake Trout is than its smaller cousin, maybe not. I sincerely doubt they ever dreamed the fish they turned loose would be the cause of our Elk population crashing.
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