Historically, Yellowstone Lake supported a population of cutthroat trout estimated at up to 3.5 million fish. In the middle 1990s, that population had declined to 2.5 million. Most recently, fisheries biologists believe the lake’s cutthroat population is now between five and ten percent of its 1995 level, or approximately 125,000 to 250,000 native fish. The culprit in the decline of the cutthroat trout is another trout, the lake trout, a non-native species likely introduced to Yellowstone Lake in the 1980s. No one is certain how the lake trout found its way into Yellowstone Lake. It may have been dumped illegally into the lake by an ignorant fishing enthusiast who hoped to create a lake trout fishery where one had never existed before. It is also possible the fish entered the lake during the Great Yellowstone Fire of 1988. Helicopters equipped with water buckets pulled water from Yellowstone Park’s numerous lakes to douse the many blazes. Crews may have inadvertently lifted lake trout out of Lewis Lake and then unknowingly carried the lake trout eggs or fingerlings into Yellowstone Lake when they went in to refill their buckets there. However the fish found their way to the deep, cold caldera lake, it is now apparent to all that they have thrived there. Lake trout have fed for decades on cutthroat trout. Biologists estimate that an adult lake trout can eat on average 41 cutthroat per year. The National Park Service wants to reverse the decline of the Yellowstone Lake cutthroat.
The service not only wants to rescue the cutthroat trout from oblivion, it also hopes a cutthroat recovery will assist all the other species that depend on the flesh-colored fish. Grizzly bears, river otters, and bald eagles are just a few of the species that rely on cutthroat trout as a food source. Those species, and dozens of others, have suffered from the diminishment of the cutthroat population. Gizzly bears have long killed cutthroat trout spawning in the tributaries that flow into Yellowstone Lake. But the fish are no longer moving into the tributaries in sizable numbers and the bears are going hungry. For example, in the past, an estimated 50,000 cutthroat annually swam from the lake into Clear Creek to spawn. That number is now down to a mere 500 per annum. Unable to find fish in Clear Creek, and other nearby streams, the big bears are looking elsewhere for food. As the bears travel further afield, they are pushing into farm country. As a result, there has been an increase in human-grizzly encounters, often with disastrous results for the bears. In the Yellowstone area in 2010, seventy-five grizzly bears either died or were removed from their home territory because of a human-grizzly encounter.
Park officials hope to arrest the decline of the cutthroat population through a program of increased gill netting. Since 1995, the service has employed gill nets as a means of decreasing lake trout numbers. However, that limited and ultimately ineffective program did not halt the increase in lake trout. In 2010, the service caught and killed 150,000 lake trout, but still the cutthroat continues to disappear from the lake’s waters. The service hopes to expand the use of gill nets in 2011, by increasing the number of fishing vessels on the lake and keeping those vessels on the water longer. But government officials admit that gill nets alone will not solve the problem. The lake trout will remain in the lake and they will continue to harm the cutthroat. The hope is that gill net operations will dent lake trout numbers enough to enable the cutthroat population to begin a rebound. In the years ahead, the park service may implement a more vigorous effort to decrease the lake trout population by killing the eggs of the lake trout in their spawning beds. The government is also considering the use of chemicals to specifically target the lake trout.
We wish the park service success in this effort. Yellowstone Lake, and the Greater Yellowstone Ecosystem that surrounds it, are two of the last areas in the United States with native cutthroat populations. Today, the fish is found in only 15% of its former range, much of that in the Yellowstone region. This issue goes far beyond just this one fish species. Cutthroat trout are vital to the health of the entire Greater Yellowstone Ecosystem. Cutthroat are a keystone species necessary to the survival of 40 other North American species. It is no stretch to claim that a threat to the cutthroat trout is a threat to a significant number of America’s most culturally-symbolic and ecologically-important species, including the grizzly bear.