Whirled away?

February 22, 2011


brown trout fish

taken from http://helenair.com/


Fifteen years ago, words like “crisis” and “devastation” were used to describe the expected impacts whirling disease would have on Montana’s fisheries after it was discovered in rainbow trout in the Madison River in 1994.
Officials called whirling disease the “single largest threat to wild, naturally reproducing trout populations in the Rocky Mountain Region.” Within a year of its discovery in Montana, the disease had spread to 14 streams, and people feared it would kill nearly all of Montana’s prized rainbow trout population. A rapidly assembled task force asked for a crash research program. State biologists harvested nearly one million trout eggs from Canyon Ferry Lake to keep the state’s fish hatcheries free from the disease.
But today, some fish biologists believe the crisis never materialized, in part because the fish adapted their behaviors.
“Back in the 1990s, when we first found it, whirling disease was a big unknown and we saw a big decline in the (rainbow trout) population in the Madison River. It was a big, scary disease that none of us knew anything about,” said Eileen Ryce, Montana Fish, Wildlife and Parks’ aquatic nuisance species coordinator. “It caused big headlines, like trout fishing was over as we knew it.
“Now that we have done all the research and are monitoring our populations, we have learned a lot, and perhaps we have learned how to live with it.”
Whirling disease was first described in Germany in 1903 and was accidentally introduced into North America in the 1950s. It begins with a parasite, Myxobolus cerebralis, which wiggles into a fish’s flesh and injects spores that attack and eat cartilage. That doesn’t bother large fish, but the young ones that are more cartilage than bones eventually bend in two and swim in circles. They can’t eat or avoid predators. Once the fish die, the spores are released into the water and are eaten by worms called “Tubifex tubifex,” and the next group of parasites starts to grow.
“Back in the late 1990s there was hope of finding a cure or silver bullet, but everyone came to the realization that’s not likely to happen,” Ryce said. “There are some places in the state we’re still very concerned about, but overall we’re just monitoring it and hoping it doesn’t spread.”
brown trout fish 2About $9 million in funding aided more than 120 research investigations that were conducted since the Whirling Disease Initiative was established in 1997, but the last of the projects concluded in 2009 and the Whirling Disease Foundation no longer exists.
Still, that research was fruitful, noted Bruce Farling, executive director of Montana Trout Unlimited.
“It was cool to see anglers, conservationists and Congress mobilize so quickly, with a lot of federal funding to research this since whirling disease is present in a lot of states,” Farling said. “We learned it manifests itself differently in different places; that different species have different resistance; and that the habitat relationship to whirling disease – i.e. cleaner streams – makes it less likely to host the worms that carry it.
“It’s also interesting that the fish figured it out before we did. They didn’t evolve in 15 years, but nature selected ways for the fish to be resistant.”
He adds that while fisheries like the Blackfoot, Madison, Rock Creek and upper Bitterroot have changed fairly dramatically in the types of fish in them, Montana remains a Mecca for people who love to fish.
“We dodged a bullet with this one, but it’s a good heads up for us to be wary about other invasive species like zebra and quagga mussels,” Farling said.
Grant Grisak, a fisheries biologist with FWP for waters below Holter Dam, is part of a four-year study that looked at trout spawning behavior to determine if that had an impact on the Missouri River population. He noted that they had been monitoring trout there since whirling disease was discovered in Little Prickly Pear Creek in 1995, which is one of the Missouri’s tributaries.
“At first, we wanted to see how it would expand and how severe the infection was,” Grisak said. “We were able to determine that 54 percent of the spawning habitat in a 74-mile stretch of the Missouri (including tributaries) is highly infected and about 57 percent of the spawning rainbow trout would use that habitat.
“So 46 percent of the habitat either had no infection or was lowly infected, and 43 percent of the rainbow trout used that habitat. So that’s about half and half, which is one reason we didn’t see the population collapse.”
Grisak’s study also involved surgically implanting radio receivers in fish to see where they spawned year after year. The results surprised him, because instead of returning to the same spot every year like salmon do, the rainbows often spawned at least 4 miles away from where they went the previous year.
“One year they might spawn in Little Prickly Pear, the second in the Missouri, and the third year in the Dearborn, or any combination of those, so it’s a highly diverse spawning strategy,” Grisak said. “That straying mechanism helps them avoid unfavorable conditions and helps them to combat that disease.”
He noted that the study also showed the trout traveled an average of 42.8 miles over a three-year period, with one putting on 324 miles.
“That’s a real mobile fish,” Grisak said.
Today, Grisak estimates they have 2,818 rainbow trout per mile on the Missouri River, compared to a long-term average of 2,933.
Ron Spoon is the FWP biologist who monitors the headwaters of the Missouri and the stretch above Canyon Ferry Reservoir. He feared the complete collapse of the rainbow population when whirling disease was found in the Jefferson River, but a study showed that the temperatures that prompted the trout to spawn weren’t conducive to whirling disease.
“So it missed the rainbows there because of the timing of their life cycles,” Spoon said. “The drought had a much bigger effect on the population than the disease, even though it’s still there at low levels.”
That wasn’t the case closer to Canyon Ferry, and Spoon said former spawning grounds like Deep Creek, Dry Creek and Confederate Creek aren’t nearly as productive due to the disease.
He noted that in other places, like Rock Creek near Missoula, the fishery changed dramatically from one featuring rainbow trout 15 years ago to a predominantly brown trout one now.
Browns spawn in the fall, when temperatures are cool, and their young hatch earlier in the spring than rainbows, which researchers said makes them much less susceptible to the disease.
“People seem to be happy with that,” Spoon said. “I think cutthrout benefited too; there seems to be a few more. So there was a shift in the community rather than the loss of an opportunity, and we all kind of adapted to it.”
Grisak added that brown trout evolved with whirling disease in Europe and are somewhat more resistant to it.
Mike Bushly, who works at The Trout Shop in Craig, said while people know whirling disease is still out there, they’re not looking at it through the same “doom and gloom” lenses as when it was first discovered. He noted that these days, people who call to book a trip are more worried about what the weather will be like in July than whirling disease.
“I know it’s still out there and really bad in certain places, but it just isn’t an issue right now,” he said. “It didn’t decimate places like it was predicted to.”



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