| Gunnison rainbow trout is on a comeback |
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| Written by Hank Lohmeyer | |||
| Wednesday, 25 February 2009 03:00 | |||
This fingerling rainbow trout brings hope for the Gunnison.
A stocking program undertaken in 2004 with the financial backing and volunteer help of area angler groups is finally bearing fruit for sport fishers. A generation of wild rainbows that emerged in the summer of 2007 has survived in large, healthy, disease-free numbers and reached the critical age of one year last summer. Dan Kowalski, an aquatics biologist for the DOW, explained, “This is the first time in my career that I’ve seen bona fide wild rainbows reaching a year old in large numbers. In previous years, the whirling disease would take up to 99 percent of all the rainbow fry before they reached a year old.” And, there is more good news for anglers from the DOW’s 2008 Gunnison Gorge trout sampling program report. “The other interesting thing is that year-old rainbows we’re finding are significantly bigger than the year-olds we’d seen in the past, even bigger than one-year-old brown trout,” Kowalski said. “This is probably some of the best news we’ve seen since whirling disease entered the river.” The DOW is also pursuing whirling disease resistant (WDR) stocking programs on the Frying Pan and Colorado Rivers. The Gunnison River rainbow trout population was virtually wiped out along with other rainbow trout in the state beginning in 1993 by the introduction of whirling disease. Whirling disease is caused by a parasite that attacks the skeletal structure of young fish causing them to deform. They become able to swim only in circular patterns, and so unable to find food they soon die. The disease attacks all trout, but the rainbows are by far the most vulnerable. The decimation of the rainbow populations in the Gunnison led to a commensurate increase in the number of brown trout in the river. The brown is affected far less by whirling disease than the rainbows are. But sport fishers prize the rainbow both for its great beauty and its highly acrobatic fighting characteristics. The DOW’s cooperative effort to with area anglers to bring back the rainbow has been so encouraging that 2009 will likely be the final year for planned stocking of WDR rainbows under the current program in the Gunnison Gorge. The DOW’s rainbow rehab efforts in the Gunnison Gorge have focused on two stretches of water — a two-mile-long section called Ute Park which spans the Delta/Montrose county line, and a four-mile-long stretch above Pleasure Park between the North Fork confluence and the Smith Fork, sometimes called the Two Forks area. The rainbow rehab project was made possible by the discovery of a rainbow trout strain in Germany that is resistant to whirling disease. This Hofer strain of fish is found in the Bavarian region. Interestingly, the Hofer strain was developed partly from crossing with a sample of Colorado rainbow trout that had been sent to Germany in 1903. The Hofer strain had developed in Germany for 100 years in water where the whirling disease is present, and so has developed a resistance. The DOW’s WDR stocking program in the Gunnison Gorge and elsewhere in the state has crossed wild spawned rainbow with hatchery raised fingerlings and stocked them in whirling disease affected waters to grow into a reproducing generation. Survival numbers of the stocked WDR rainbows were expected to be quite low the first two or three years of the program, and in fact they were, Kowalski explained. But the generation of fry which emerged in 2007 has shown good survival results and holds promise to become the core for a reproducing population of rainbows in the gorge. The DOW is still watching to see an increase in rainbow numbers in the Pleasure Park area. “The number of rainbow fry we find down there is very low. We’re estimating only about 500 rainbow fry per mile, whereas it was routine to get from 3,000 to 5,000 rainbow fry per mile in the 1980 and early 90s,” Kowalski said adding that, “The rainbow fry sampled here are larger than previously and exhibit far less signs of whirling disease. “Five years ago, 99 percent of all the rainbow fry you found in the river would have clinical symptoms of whirling disease. Now as few as 30 percent of the age zero rainbow fry exhibit any clinical symptoms of the disease.” But the story isn’t all good news yet. Kowalski explained that, “As far as the WDR fish, the bad news is that stocking these fish since 2004 hasn’t really increased the rainbow numbers. There are just so many brown trout in the water now that just adding a few more WDR fish really isn’t adding to the system. We have seen biomass increases in the Pleasure Park region and below Pleasure Park. The Biomass of rainbows has increased appreciably in those two reaches of the river. “So while there hasn’t been a large increase in the rainbow trout biomass riverwide, The good news is that the rainbows there are growing well and they are reproducing. In 2007 and 2008 we have seen the first reproduction of these whirling disease resistant fish. And 2008 is the first year we have seen the WDR rainbows grow to one year of age.” The population of wild rainbows in the Gunnison hopefully will take advantage of the leg up the DOW’s stocking program has given it and return the stretch of river to the world class rainbow sport fishery it once was. But nothing is guaranteed, and there have been challenges. “It’s pretty common to see low survival rates for planted rainbows the first few years,” Kowalski said. “After that, when the survivors become adapted to the wild environment, they take off and do real well. That’s what we are hoping is going to happen with these WDR rainbows in the Gunnison. Survival has been pretty low the first couple of years, but now that we’ve finally got that foothold and reproduction has occurred we are hoping the survival will increase.” Looking forward, the DOW is planning now to conduct one more stocking of the Gunnison with the WDR fish this year in October. “A footnote to all this is that previous to 2004 the Gunnison Gorge and the Lower Gunnison River were classified as a wild trout water. We decided to undertake this stocking program to try and bring the rainbows back that had been knocked out by whirling disease,” Kowalski said. “Now that we have finally seen some success in that program, the plan is that we want to introduce one more WDR class of fish into the river. Then we want to back off and cease that stocking plan altogether, return the river to wild trout management, and we feel there is enough disease resistance in the population now that natural selection can occur in that population and hopefully select for a wild rainbow trout population that will thrive in the Gunnison Gorge like it did in the 1980s.”
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