One of the most important of these is the Yellowstone cutthroat trout. Each spring, this trout runs up out of Yellowstone Lake into the tributary streams to spawn. Trout provide an important food for Yellowstone bears. But in recent years, the trout runs have been on a decline. There are a couple of reasons for this.
The first is the introduction of lake trout into Yellowstone Lake, discovered in 1994. Although no one knows how the lake trout got there, Yellowstone National Park officials don't want them. Lake trout are difficult for anglers to catch because they generally swim in much deeper water than trout. What's more, they are voracious predators and eat the native cutthroat trout like popcorn. Officials have been attempting to eliminate lake trout from the reservoir by having no limit on the catch for anglers, as well as launching an aggressive netting campaign.
Perhaps even more alarming is the fact that a deadly disease called whirling disease has made its way into the system. Whirling disease was first documented in Colorado fish hatcheries several years ago. The disease destroys the central nervous system of young fish, causing them to spin in circles, or "whirl." It is a fatal fish disease that impacts cutthroat trout. The disease can be spread through fishing equipment such as waders taken from an infected stream to a non-infected stream.
Pelican Creek, which is a major tributary, has been documented with whirling disease, and today this creek is almost devoid of Yellowstone cutthroat trout, which is not good news for Yellowstone bears.
Yellowstone National Park bears also depend upon the highly nutritious nut of the whitebark pine. This high altitude tree produces a purple pine cone loaded with pine nuts. Each fall, as the pine nuts ripen, grizzlies go into the high country to dine. Here they may stay for several weeks as they load up on the pine nuts in preparation for the winter hibernation season. Unfortunately, there is trouble on the horizon. A disease called blister rust is impacting whitebark pine, and many of these trees are dying. Scientists are looking at a number of other factors as well that may be hurting the pine, and in turn hurting the grizzly. Global warming and acid rain may also be factors.