Progress being made on disease that kills trout, salmon
Aspen, CO Colorado
FORT COLLINS, Colo. ” Ken Kehmeier vividly remembers that day 17 years ago when everything changed ” the day whirling disease first was discovered in the Poudre River.
Kehmeier, the Colorado Division of Wildlife’s fishery biologist for the Poudre, North Platte and Laramie river systems, was doing a routine check at one of six testing sites along the Poudre. The tests previously had been done on an annual basis, but after the tests produced the same negative results year after year, the decision was made in 1988 to test the water every two years.
Two years later, when Kehmeier returned to sample the Poudre, tests proved that whirling disease ” a potentially devastating malady that can wipe out populations of trout and salmon ” had arrived.
“To this day, that bugs me more than anything else in my career,” the 22-year DOW veteran said. “I feel like I missed something, and it came back to haunt us.”
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Whirling disease attacks young fish when their skeletons still are cartilage. While the fish don’t always die, the parasitic disease often deforms fish and can cause them to display the tail-chasing behavior that gives the disease its name.
There are signs that the Poudre ” and the battle against the disease ” is changing. Kehmeier said Poudre rainbows are reproducing naturally for the first time in many years, and the young trout seem to have a built-in resistance to whirling disease.
Elsewhere, certain types of the tubifex worm, which carries the infection and transmits it to fish when eaten, have shown resistance to whirling disease. Biologists are studying the worm in hopes of discovering a way to biologically control the disease.
Kehmeier’s early studies found that fewer and fewer rainbow trout ” the Poudre’s primary tenant ” were in the river. Entire generations of young fish had been wiped out by the disease, leaving only a few larger adults, which are more resistant to the disease.
“Over time, there were only a very small number of rainbows in our test samples,” he said. “There were years when I didn’t catch a single rainbow at a particular testing area. It was really disheartening from the standpoint of, you spend your life trying to create better fishing and, all of a sudden, you are battling something you have no control over. It really reaches out and takes a shot at you.”
Kehmeier was not alone. One by one, most of the state’s great fisheries fell victim to whirling disease. In 1993, nearly all of the young rainbows in the Colorado River as it flows through Middle Park had been wiped out. Entire generations of brook and cutthroat trout also disappeared.
Currently, the disease appears in 13 of the state’s 15 major river drainages and in 11 of the DOW’s 16 trout production facilities. The Watson Lake Rearing Unit northwest of Fort Collins continues to test positive, but the Bellvue Hatchery located a short distance from the Watson facility is clean.
And it’s not just Colorado’s problem, either. To date, 23 states have detected whirling disease, and that number seems to be growing. Whirling disease has invaded nearly every Western state, and wildlife commissions have spent tens of millions of dollars battling the malady.
On the Poudre, the disease still is very much alive. However, the initial shock created by the arrival of whirling disease in 1990 has been replaced by new strategies and new hope that have helped the Poudre maintain its status as a destination fishery.
“We’ve learned to manage around it,” Kehmeier said.
One of the key moves was to make brown trout, which are naturally resistant to whirling disease, the Poudre’s primary resident. Prior to the disease’s discovery, rainbows made up 60 percent and browns 40 percent of the Poudre’s population.
Currently, 95 percent of the Poudre’s trout are browns.
That has changed the nature of fishing. Anglers love rainbows because they are great fighters and tend to be a bit easier to catch. Browns are fighters, too, but they are more cautious and more elusive than rainbows.
Jim Ferguson, who has been fishing the Poudre since 1968, said whirling disease has had a profound effect on the river.
“Before the disease, a really good day was catching 20 or 30 fish, and most of them were rainbows,” said Ferguson, who owns Angler’s Roost in Fort Collins. “Now, a good day is six to 12 fish, and they almost always are browns. I’m a fishing addict, and I like fishing for wild fish, but a lot of people just want to catch a lot of fish.
“Those people probably don’t like the way the river has changed.”
In addition to the trends in rainbow reproduction the worm’s resistance to the disease, the state has imported from Germany the Hofer rainbow trout, which has natural resistance to the disease. It has initiated programs to crossbreed the Hofer with traditional rainbows. Early results are promising.
Still, it likely will be some time before the Poudre returns to its former self.
Kehmeier said brown trout, which are naturally territorial and aggressive, have taken over traditional rainbow sections of the river.
“I think it would be difficult to establish rainbows at the level they were before because browns are so competitive,” he said. “But right now people seem to be happy catching browns, which is good.
“What happened to the Poudre is a travesty, but we’ve been able to survive and create a fishery people are happy with. That’s why we’re here.”
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