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The destruction of the kokanee fishery reverberated through the Flathead ecosystem, affecting even non-aquatic animals. Flathead Lake kokanee spawned at McDonald Creek in Glacier National Park. When the fishery was robust, this swarm of pink flesh attracted the largest concentration of bald eagles in the United States. In one week in 1983, researchers counted 639 bald eagles at McDonald Creek. In 1989, they counted 25.
"These aquatic invasive species can completely alter the food webs of lakes and rivers," says Ellis. "I've been here [on Flathead Lake] working for 30 years, and it's like I'm working on two different lakes."
The Mysis introduction is an extreme example of a more general phenomenon: Aquatic invasive species are a threat to fisheries, but fisheries management is sometimes at the heart of aquatic invasions. After Mysis warped Flathead Lake's food web, fisheries scientists began noticing declines in wild rainbow trout in the Madison River, in southern Montana, in 1991. By 1994, the fishery had dropped to about 90 percent of its historic average. Lab results on the rainbow trout came back positive for a familiar but unexpected pathogen: whirling disease.
Whirling disease—so named because it attacks the nervous system and causes fish to swim in a spiral—had been a known problem in U.S. fish hatcheries since the 1950s, but it wasn't considered a threat to wild populations. The discovery of the disease and its role in decimating wild trout in Montana and Colorado rivers in the 1990s shocked fisheries scientists. Funding at state and national levels kicked research into high gear, resulting in rapid progress on the biology of the disease, with the ultimate goal of eradicating it.
Yet despite millions spent on research, agencies have not been able to halt the expansion of the disease, let alone stamp it out. It continues to spread to other drainages; and though rainbow trout in the Madison have recovered from their low, they are still 30 to 40 percent below historic levels.
The deadliest fish disease
On March 15, at Polson, on the shore of Flathead Lake, dozens of scientists and land managers gathered for the Crown Managers conference. It's an annual event for agencies involved in the Crown of the Continent, a 28,000-square-mile ecosystem that encompasses much of northern Montana, including Glacier National Park and Flathead Lake, as well as neighboring lands in Canada. Present were representatives from the Forest Service, Glacier, the Confederated Salish and Kootenai tribes, and many state and local government agencies from Montana, British Columbia, and Alberta. The discussions were consumed by the past, present, and future of aquatic invasive species. The introductory speaker, Mary Sexton, director of Montana's Department of Natural Resources and Conservation, set the tone for the conference: "We have an opportunity to collaborate before aquatic invasive species become a full-blown crisis," she said.
For the next three days, the scientists and managers hashed out the status of aquatic invaders in Montana and the Crown, and how future invasions might be averted. According to Eileen Ryce, the keynote speaker and Montana's invasive species coordinator, many aquatic invaders are already in the state. In addition to Mysis shrimp and whirling disease, Montana has several aquatic invasive plants. Since 2007, Eurasian water milfoil has spread over the Noxon and Cabinet reservoirs, where it now covers 400 acres. An environmental assessment of the reservoirs indicates that the weed has the potential to cause damage. Eurasian milfoil forms dense canopies that shade native aquatic plants. It can reduce food for fish, and it may particularly affect salmon and trout by covering the gravel beds where they spawn. The weed also ruins swimming areas, clogs water intakes, and fouls the air when it decays. Milfoil invasions have reduced lakeside property values by 15 percent in the Midwest, according to invasive species educator Doug Jensen, hurting not only property owners but state coffers.
Western Montana has other aquatic invasive weeds. Yellow flag iris is well established in four counties in northwest Montana, and flowering rush covers over 2,000 acres in western Montana. Like Eurasian milfoil, these plants threaten native fish and can ruin swimming areas. They can also be very costly to irrigation systems. In Idaho, canals infested with flowering rush have to be chained every two to three years to maintain proper water delivery.
Still other, potentially more destructive invaders loom on the horizon—and Montana may be particularly susceptible to them.
According to Jensen, 14 million boaters move frequently between water bodies in the United States. Montana's ample and attractive waters are a destination for many of them. The state contains 750,000 acres of recreational water, said Ryce. Forty-one percent of anglers licensed in Montana are non-resident, and all told, non-resident use adds up to a total of 800,000 angler days—which means a lot of fishermen coming and going from the state. And one third of Montanans are licensed anglers, which means there is a high potential for in-state anglers to transport invasive organisms on boats, bait, or fishing gear. Popular water bodies used by these anglers can serve as stepping stones to spread aquatic invaders across the Continental Divide. "The two most likely introductions for mussels in Montana are Fort Peck Reservoir and Flathead Lake," said Ryce. "Canyon Ferry Reservoir [near Helena] links these two together. It's usually rated number-one by resident anglers."
If viral hemorrhagic septicemia, Asian carp, or invasive mussels made it into Montana, they'd find a welcoming habitat in much of the state—and their effects would be alarming. "VHS would be deadly to pretty much all the fish species we have here in the state," says Ryce, whose scientific training is in fish diseases.
"It's the deadliest fish pathogen we've ever seen."
Those fish that don't die from what has been called the ebola of fish could spread VHS and re-infect fish populations. "Typically what you see when it gets introduced into a new population is a very dramatic fish kill, and then survivors within the population act as carriers for the virus," said Ryce. "During times of stress, after the population has rebounded, you'll see another die-off or fish kill, but it never completely leaves the systems. So you often see this cyclical event of large fish kills."
Several species of fish are categorized as Asian carp, and at least three of these could invade parts of Montana. "The silver and bighead carp are more of a concern for the lower Missouri and lower Yellowstone, but the grass carp can survive in western Montana and we know they have in the past," said Ryce. "They are certainly a threat."
VHS and mussels are likely to come into the state in boats or bait, vectors that could also introduce Asian carp. Another route for some invasive species is aquarium shops and pond supply stores. Aquarium stores in Montana have sold Eurasian water milfoil in the past, and aquatic gardeners have introduced aquatic weeds like yellow flag iris to Montana. Selling and buying invasive species in the state is illegal, but even as agencies work with commercial sources in the state, there is only so much they can control.
"We have found grass carp in private ponds. That is where we have the most problems with them," said Ryce. "People introduce them to control aquatic vegetation. It would be illegal to buy them, but you know you can get anything online."
Most websites that sell grass carp are frank about which states require grass carp permits or have banned grass carp altogether, and none mention delivery to Montana. But other states, including Wisconsin and Texas, have had instances of illegal shipments of grass carp into their state. Arkansas in particular has been a source of these illegal shipments.