Millions of visitors are drawn to Yellowstone National Park from around the world to observe its wildlife. But the food chain that supports this abundance may be on the verge of collapse. The cutthroat trout, which is considered a "keystone" species for the ecosystem, has been devastated by the triple whammy impact of lake trout, whirling disease, and drought in Yellowstone. Their population crash threatens to have a domino effect up the food chain.

WOC is following the situation in Yellowstone closely. We are drawing public attention to the situation in an effort to raise the level of urgency and get the park to do more before it is too late. And, at a very tangible and enjoyable level, encouraging anglers to go fish the Yellowstone Lake area for lake trout.

Ten or so years ago, if you tossed a lure or fly into Yellowstone Lake, you were almost guaranteed to come up with a catch.

"A writer in the 1980s said ‘Yellowstone Lake is not a trout fishery, it’s a trout catchery,’" says John Varley, the director of the Yellowstone Center for Resources. "We used to tell parents to take their kids to Yellowstone Lake because they’d catch a fish there. No one is saying that anymore."

Where have all the fish gone?
The population of Yellowstone’s cutthroat trout was once estimated to be 2.5 million ‘catchable’ sized fish in the Yellowstone Lake area. Scientists estimate that number has dropped by approximately 75 percent. This population collapse has the potential to cause a ripple effect.

Approximately 42 species of mammals and birds rely on the cutthroat for part or all of their nutritional needs. In addition, thousands of anglers flock to the park annually to try their hand at its world-renowned fishing.

"Is the whole food chain around Yellowstone Lake on the verge of collapse? I have to say, ‘Not yet’," Varley says. "Are cutthroat doomed? I would guess not. Between the help humans can give them and their own inherent resilience, I would give them a fighting chance."

It’s ironic that the cutthroat’s survival in Yellowstone appears dependent on human interference since their current plight is largely due to human actions. Non-native species and disease—lake trout and whirling disease specifically—have had devastating impacts on the cutthroat population and both were brought to the park by people, either inadvertently in their tackle boxes or with the misguided hope of improving the fishing.

Lake Trout
In 1994, non-native lake trout were discovered for the first time in Yellowstone Lake. Their presence caused immediate alarm. Lake trout (salvelinus namaycush) are voracious predators. In other lakes in the inter-mountain West where lake trout have been introduced, cutthroat trout were eliminated or severely reduced. Why? A single large lake trout can consume 50 or more cutthroat trout each year.

Yellowstone Lake represents the largest remaining intact natural habitat of Yellowstone cutthroat trout (Onchorhynchus clarki bouveiri) in existence. When white settlers first began colonizing the western United States, there were probably 14 subspecies of cutthroat trout. Now, two of these subspecies are extinct and eight of the remaining 12 were listed by the American Fisheries Society as endangered, threatened or of special concern in 1988.

Yellowstone cutthroat was considered one of the few success stories at that time. Human activities had reduced its range to 15 percent of its historic distribution, but the Yellowstone Lake area was seen as the last great refuge for the fish. No more.

"It was always the lake that was the savior," Al Zale, the leader of the Montana Cooperative Fishery Research Unit in Bozeman, told the Billings Gazette in June. "Then we had whirling disease and lake trout and suddenly we’re realizing we had a lot of eggs in that one basket."

A group of lake trout specialists from the United States and Canada gathered in the park in 1995 to share information about the consequences of the presence of lake trout in Yellowstone. These experts foresaw the current cutthroats’ plight. They also foretold of staggering economic losses resulting from the collapse of the world-famous cutthroat sport fishery in the Yellowstone Lake area.

Buy Out versus Pay Out

It's ironic that the cutthroat's survival appears dependent on human interference since their current plight is largely due to human actions.

In the "The Lake Yellowstone Trout Crisis Executive Summary," released in 1995, the value of the fisheries surrounding Yellowstone Lake was said to be worth more than $36 million per year, or more than a billion dollars over 30 years. With the loss of the cutthroat, that figure could drop to roughly 400 million. Or so the experts predicted.

Their predictions are proving remarkably accurate, although to date, no numbers have been attached to the economic losses or to the ripple effect the cutthroat’s decline is having on other species. It’s happening, but it’s hard to tell how much and how.

"The number of anglers fishing Yellowstone Lake has diminished substantially," Varley says. "Approximately half of the number that were observed in 1994—the year lake trout were discovered—were there in 2003. A lake trout fishery, which is small by comparison, obviously has not been an economic replacement for the cutthroat fishery. We have not calculated dollar losses, however."

One link in the food chain
The experts also worried about the effect of the demise in the cutthroat population on the animals that eat them. These animals include grizzly bears, bald eagles, osprey, white pelicans, river otters, even American dippers. Not all of these species depend wholly on the cutthroat, but all derive important nutrients from the fish at certain times of the year.

Lake trout, which live at much deeper levels in lakes and do not venture into streams to spawn, will not readily fill the niche left by the cutthroat they displace. The mystery here is that the park’s researchers have not yet seen the decline in the predator populations they predicted, even amongst the osprey and white pelicans that depend solely upon cutthroat for sustenance. There’s some indication that fewer grizzlies are frequenting cutthroat spawning runs, but even that evidence is largely circumstantial.

"Without the cutthroat, we’d expect these species should do poorly, but the Park Service has not seen any demonstrable effect yet," Varley says.

"We are not able to monitor all 42 species to check their population trends," Varley concedes. "But we do monitor the big birds, some of which are obligate fish eaters—osprey, white pelicans, cormorants. We have not seen population declines to date even though their principal food supply is down 75 percent, and there is no evidence they have ever eaten a single lake trout.

"This puzzles us some, but pelicans and osprey can nest on Yellowstone Lake and fly to nearby unaffected waters [to fish]. It’s hard to believe they can do this without incurring a ‘cost’ but we have not found one to date," he says. "It doesn’t make sense," he adds.

It’s more than just the lake trout

Varley is hopeful that, with help, the fish will survive. But not everyone shares his optimism. It would be one thing if lake trout were the only thing the fish had to contend with, but they are not. "Lake trout don’t get all the blame [for the cutthroat’s demise]," Varley says. "A decade of drought has reduced cutthroat fry recruitment, and trout whirling disease, first discovered in the lake in 1998, is reducing fry in certain lake tributary streams to near zero."

Whirling disease is caused by a parasite that came to America from Europe—probably with imported European trout—and a common aquatic tubifex worm. The parasite becomes engulfed by the worm, which acts as an intermediate host. Eventually, this relationship produces a new free-floating life phase of the parasite that attaches itself to trout and salmon.

The parasite then penetrates the head and spinal cartilage of the fish, where it multiplies rapidly, putting pressure on the organ of equilibrium. This causes the fish to swim erratically (whirl) and have difficulty feeding or avoiding predators. Eventually they die.

"Pelican Creek, which is Yellowstone Lake’s second largest tributary, is whirling disease heaven," Varley says.

"There used to be 40 to 50 thousand [cutthroat] spawners in Pelican Creek a year. Now it’s a bust. There’s nothing.

"Unless we get something really new as a tool, there’s nothing we can do about whirling disease," Varley says. "The fish are going to have to solve the problem themselves."

Other trout, such as the brown and bull trout, are very resistant or have some immunity to whirling disease. Varley says there are some cutthroat survivors in heavily infested streams in the park, which gives him reason to hope that cutthroat too can build up resistance over time. But, he concedes, they’ll need to get a break from Mother Nature and lake trout to succeed in battling off the disease and building up immunities will take decades or longer.

Human intervention
Humans have not always been the cutthroat’s friend. For some reason, Varley says, there are people who feel compelled to plant non-native fish in cutthroat habitat. This practice at best cuts down on cutthroat numbers, at worst wipes them out.

"I think some evil-doer put the lake trout in Yellowstone Lake," he says. "Every good trout lake in the West is being subjected to unofficial plants of lake trout, northern pike, walleye, etc… There are some weird renegades out there who love these other fish and want to plant them everywhere. It is costing the government roughly $300,000 a year."

Anglers are also the probable culprits for bringing both whirling disease and New Zealand mud snails—which are having a negative impact on aquatic insects in some drainages—into the park. Only drought seems beyond human blame, unless you want to link it to global warming.

In spite of human’s bad track record, Varley believes the only reason cutthroats stand a chance is because of the work the park is doing to control the lake trout and limit the spread of whirling disease. In other words, people are their last hope.

Park officials are aggressively fishing lake trout in Yellowstone Lake with the use of gill nets. Since 1996, they have taken more than 75,000 lake trout from the lake. Furthermore, the park has seen their catch rates drop off over the years, which they believe corresponds to a decline in the lake trout population. During the lake trout’s fall spawn—which runs from mid-September through October—the Park Service is destroying large numbers of fish while they are in concentrated areas around West Thumb. If they are able to destroy the fish prior to spawning, they are able to reduce the numbers even further. Anglers are encouraged to fish and required to kill any lake trout they catch. The park has even considered offering a bounty on lake trout.

"It is good news that the lake trout gill net catch… is declining. This signals that we are fishing a smaller population," Varley says. "The average size is declining, which is also a good sign because it means fewer spawners and fewer eggs laid.

"It is good news that we have been unable to detect declines in the species that depend on cutthroats for food to date," he continues. "It is good news that all tributaries to the lake don’t have the same rate of whirling disease infection. And it is good news that in a declining federal budget atmosphere, the agency and congress have funded the effort to try to save cutthroats.

"So it is not hopeless. We continue to think we can help make a difference," Varley concludes.

Are park officials downplaying the situation?
David Haire, a water-quality scientist and certified fisheries scientist who works as a fisheries consultant in Wyoming, thinks the park is not taking aggressive enough action.

"Lake trout, whirling disease, and drought—wham, wham, wham," Haire says. "And I might throw in the fourth wham—lack of urgency on the part of fish biologists. "Stopping fishing for cutthroats in the lake’s watershed should have been done a decade ago, when the lake trout were found. If the [cutthroat] population has declined so much, how can the Park Service continue to allow fishing there? Money is the likely answer."

Haire is not alone. Chris Fissell, a senior staff scientist with the Pacific Rivers Council told the Billings Gazette that the government shouldn’t wait too long before taking steps to protect the cutthroat. His group is one of a coalition of environmental groups challenging a federal decision in 2001 not to list Yellowstone cutthroat as an endangered species.

"I think it’s a species on the cusp of a fairly major decline in Yellowstone," Frissell said. "They’re tough critters and the fact that they have this natural ability to hang on gives you optimism. But we’ve got to stop hitting them with this relentless onslaught of threats."