State officials hope wild trout populations will thrive again
February 5, 2008
ASPEN ” For the first time since whirling disease decimated most naturally reproducing rainbow trout populations in Colorado more than a decade ago, a new strain of the sport fish has reproduced naturally. The breakthrough took place in ponds along the Fryingpan River above Basalt.
A second population of the new cross-breed of trout has spawned successfully in the Gunnison River, according to state wildlife officials, giving rise to the hope that wild, self-sustaining rainbow trout populations will thrive once more in Colorado rivers. Since the mid-1990s, whirling disease has prevented naturally reproducing rainbows from thriving by wiping out generations of fingerlings.
The new strain, a cross between the Hofer rainbow trout and other trout used for stocking purposes, appears to be resistant to whirling disease, according to the Colorado Division of Wildlife (DOW) Even more encouraging, so are its offspring. “We’ve pretty much known that the Hofer crosses are resistant, but we finally got actual proof through genetic testing that their fingerlings are, as well,” DOW spokesman Joe Lewandowski said.
The fish in the Gunnison, and in ponds on private property along the Fryingpan, were hatched in May 2007. They were captured in October when DOW aquatic researchers conducted electro-fishing operations in both areas. Several of the fish were sent to a laboratory in Boulder for genetic testing that verified that the trout were offspring of Hofer-cross rainbows stocked in the Gunnison starting in 2004 and in the ponds in 2005.
Hofer-cross fingerlings also were stocked in the upper Colorado River near Kremmling in 2006, but researchers found no young fish there in 2007. The cold water of the Colorado might mean the fish are maturing more slowly than in the warmer Gunnison River and the Fryingpan ponds, though. Researchers suspect the fish in the Colorado have not yet reached sexual maturity. They’ll look for young fish again in the fall of 2008.
And, the Hofer-cross populations in the Gunnison and Fryingpan ponds will be checked again this fall to make sure they’ve survived and are continuing to reproduce. The DOW already is ramping up to rear millions of the new cross strain in its hatchery facilities for stocking in lakes and rivers around the state in the years to come, Lewandowski said.
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In 2008, more than 1 million sub-catchable and catchable fish of the Hofer-cross strain will be stocked throughout Colorado. Where exactly the trout will be released this year has yet to be determined, Lewandowski said.
Locally, the Fryingpan and Roaring Fork rivers will see stocking with the new strain at some point, he said. Naturally reproducing strains of rainbow trout might relieve the DOW of some of its burden to produce rainbows for stocking purposes. Anglers, though they won’t be able to spot a Hofer-cross when they land one in the net, might appreciate the new strain, as well, Lewandowski said.
They seem to get bigger faster, and a wild fish generally is a more wily adversary than their hatchery-reared counterparts.
“Hatchery fish are hatchery fish,” Lewandowski said. “We’re very hopeful we’re going to have real, sustainable trout populations reproducing in the wild.”
Whirling disease, found in Colorado in the mid-1990s, is caused by a microscopic parasite that passes through a fish’s skin. It attacks the cartilage of young fish and distorts the spine ” the affected fish move in a whirling motion when excited or trying to escape a predator, reducing their ability to survive in the wild. Rainbows proved especially susceptible, while brown trout are not.
In the past, the DOW has stocked 10-inch rainbows in the state’s rivers ” fish that are mature enough to resist whirling disease, but haven’t reproduced successfully, as their young fall victim to the parasite. That’s not the case with the Hofer-cross fingerlings.