We've all got a stake in this invasive species project, because it involves a sparkling jewel in one of our national treasures. The setting is Yellowstone Lake, in Yellowstone National Park, and the invasive species playing the part of the antagonist in this story is the lake trout (Salvelinus namaycush). Most people, fishing enthusiasts included (particularly easterners like me), probably would not think of a lake trout as an invasive species in any North American lake, including Yellowstone Lake. But as I learned just a few months ago when I stumbled onto this story, lake trout are not native to Yellowstone Lake. And the National Park Service's effort to eradicate (yes, I said eradicate) them from Yellowstone Lake is far more than just a matter of ecological anal retentiveness.
The Problem
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| Lake Trout taken from Yellowstone Lake. (National Park Service photo) |
Lake trout are believed to have been introduced to Yellowstone Lake in the mid-1980s. The first recorded lake trout caught in Yellowstone Lake was in July 1994, and within weeks several more lake trout catches were documented by park rangers. Lake trout are native to the northeastern U.S., the Great Lakes, and Canada. They live in big lakes, because they require high levels of dissolved oxygen found in the cold depths of big lakes. So Yellowstone Lake probably seemed like a logical location for an unwitting angler to surreptitiously introduce lake trout.
The problem with lake trout, which grow much larger than other trout species, is that they don't work and play well with other fish. They are piscivores, meaning that they feed almost exclusively on other fish. And that dietary preference has been bad news for the cutthroat trout native to Yellowstone Lake.
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| Yellowstone Cutthroat Trout. (National Park Service photo) |
Cutthroat trout (Oncorhynchus clarkii) are a beautiful fish that we in the eastern U.S. have to go west of the Rocky Mountains to experience. They get their name from the red slash of color along their lower jaw. The ecologically cool thing about cutthroats is that, through geographic isolation in various major drainage basins throughout the western U.S., they have evolved into at least 10 distinct subspecies. And Yellowstone Lake, the source of the famous Snake River that slithers through Idaho and eventually into the Columbia River in Washington, is home to the Yellowstone cutthroat subspecies (Oncorhynchus clarkii bouvieri). This subspecies is found only in Yellowstone Lake, Yellowstone River, and the uppermost Snake River.
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| Yellowstone Cutthroat Trout. (National Park Service photo) |
Lake trout spawn deep in the lake, so they will never be present in the shallow parts of the lake or in the tributaries to be a dietary opportunity for their bird or mammal neighbors in the park. The Park Service estimated in 2010 that the lake may have lost up to 99% of its spawning cutthroat trout because of predation by lake trout. Not only did the introduction of lake trout into Yellowstone Lake deal a significant blow to the lake's cutthroats, the depletion of cutthroats rippled throughout the Yellowstone ecosystem to species that had depended on feeding on the cutthroats' spawning runs. There were even reports of grizzlies coming down from the hills in search of food when they formerly would have been content in the upper reaches of tributaries chowing down on spawning cutthroats. So the need for the Park Service to address the plummeting population of Yellowstone cutthroats was far more than an attempt to save an important sport fishery in a popular national park. The balance of the greater Yellowstone ecosystem was threatened by the loss of native cutthroats.
The Solution (eventually, hopefully)
The National Park Service has been gill-netting lake trout in Yellowstone Lake since 1995. The Service operates its own boat that deploys a chain of gill nets through areas that are known lake trout migration routes in the lake. The nets, many set as deep as 150 to 160 feet and left in place for several nights, recover hundreds of mostly dead lake trout when pulled up.
The Park Service also contracts with a commercial fishing company that operates a trap-netting boat in the lake. These trap nets are designed to recover the fish alive so that cutthroats that are caught along with the lake trout can be released. It's estimated that about 50 lake trout are caught in the trap nets for every one cutthroat.
Whether the lakers are caught in the Park Service's gill nets or in the contractor's trap nets, all recovered lakers are killed, weighed, and sexed by Park Service staffers and student volunteers before having their air bladders punctured and being tossed overboard deep into the lake. It's likely that trying to dispose of the huge volume of dead fish on land would soon create a solid waste headache that would attract bears like a moth to a flame.
Any lake trout caught by anglers in Yellowstone Lake are required to be killed by the anglers. Catch and release of lake trout is prohibited at Yellowstone.
Yellowstone fisheries program supervisor Todd Koel estimated that there were probably around 500,000 catchable lake trout in Yellowstone Lake this spring. Contrast that number with an estimated 4 million cutthroats, at their peak numbers prior to the introduction of lake trout, in Yellowstone Lake and its tributaries. Now, however, Koel estimates there may be only around 400,000 cutthroats in the lake and its tributaries, and those cutthroats continue to be preyed upon by the lake trout.
Results
The Park Service acknowledges that there is only a slight chance that lake trout can be eliminated from Yellowstone Lake, but experts think that aggressively removing large numbers of lake trout is feasible to keep their population in check in the lake. According to a newspaper story last month from nearby Powell, Wyoming, last year's lake trout harvest totaled 224,000 fish, and this year's total was 274,000 lake trout killed by the cutthroat restoration program. And the Park Service is looking at ways to kill lake trout eggs in their spawning beds to increase the program's effectiveness.
The Park Service had budgeted $1 million this year for the cutthroat restoration (ie. lake trout elimination) program. That budget has been supplemented by an additional $1 million from the Yellowstone Park Foundation. Other conservation organizations, such as the East Yellowstone Chapter of Trout Unlimited, the National Parks Conservation Association, and the Greater Yellowstone Coalition are also stepping up to help out.
The kind of public/private collaboration that has come together to save the Yellowstone cutthroats has been reassuring, and the program's results over the past 18 summers have been encouraging. And if I had to identify a take-home message from this story, I think it would have to be: An ounce of education is worth a pound of cure. In this situation, it is likely that anglers, ignorant of the effects of their actions, were the source of the original lake trout planted in Yellowstone Lake. The resulting crash of the Yellowstone cutthroat population, after nearly 20 years of earnest restoration efforts, and tens of millions of dollars invested, could have been avoided if anglers had been better educated about the ecology of the sport of fishing that they presumably love.
Ecology is a science. Whether we identify ourselves as anglers, exclusive fly fishers, conservationists, ecologists, or something else, we need to advocate for quality science education in our schools. Science-savvy students grow up to be science-savvy adults who can be careful and effective stewards of our natural resources.
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