Rainbow trout are back.
Well, sort of. And depending on who you ask, they never were really that prominent.
According to Colorado Parks and Wildlife, after being devastated by whirling disease in the 1990s, rainbow trout populations are on the upswing in most major rivers in the state, thanks to a 20-year effort by CPW aquatic scientists and biologists, the agency said.
Brown trout, which are resistant to whirling disease, have dominated the Animas for years, so the disease likely wasn’t as noticeable in these parts.
“Whirling disease hit all the major rivers and smaller streams throughout the state,” said Joe Lewandowski, Colorado Parks and Wildlife public information officer in the southwest region in Durango. “This was not just a Front Range issue. It was a bigger issue on the West Slope because we have more quality trout water. And yes, it also affected the Animas River – although brown trout have long dominated the Animas, and browns are resistant to whirling disease.”
Whirling disease is caused by a spore that very young fish and deforms their spine, causing them to swim in a whirling pattern. They die shortly after becoming infected. When whirling disease hit Colorado’s rivers, natural reproduction of the species virtually ended. That allowed brown trout to become the dominant sport fish in Colorado rivers.
According to the CPW, the whirling disease problem started in 1986 when a private hatchery unknowingly imported infected rainbow trout from Idaho that were then stocked in 40 different waters in Colorado. The disease eventually spread throughout the state and even CPW hatcheries, which caused more waters to be infected. And by the mid-1990s, rivers in Colorado and other western states were thoroughly infected, the CPW said.
Still, anglers in the state continued to catch rainbows.
“Some people have wondered why they were still catching rainbow trout during this period – they were catching trout that CPW stocked in rivers, lakes and reservoirs,” Lewandowski said. “Our hatcheries were cleansed of whirling disease and were still able to produce trout. The big deal with this is that we now have natural reproduction of rainbows in rivers and streams, thus we have truly wild fish. And now there are two species to catch – browns and rainbows. With natural reproduction, CPW eventually will be able to dial back the number of fish it needs to stock.”
The current stocking effort is a fairly extensive one as the CPW attempts to bolster rainbow numbers. And in the Animas, too.
“We are making a major effort to stock the whirling disease-resistant rainbows, mostly fingerlings – 3-inch fish – throughout the Southwest,” Lewandowski said. “The Dolores and West Dolores rivers, mainly above McPhee (Reservoir, in Montezuma County), will be getting 60,000 fingerlings, (with) 30,000 to the East and West Forks of the San Juan, 11,000 to the Piedra, 5,000 to the Rio Blanco south of Pagosa Springs, and Williams Creek north of Pagosa will be getting 5,000. Eventually, biologists will be doing some electro-fishing in these waters to see how the fish are doing.”
The CPW has experimented with Hofer rainbows – a variation brought from Germany in the early 2000s that supposedly are immune to whirling disease – with some success in recent years, mostly on the Front Range. It’s not yet known how they’ll do here, Lewandowski said.
“The Hofer crosses have been stocked in the Animas, but we’re still not sure of how these fish will fare in the Animas because of water-quality issues, and because the federal government stocks 50,000 rainbows annually as ‘mitigation’ fish for the Lake Nighthorse project,” he said. “In the Animas last year, 10,000 of the (Hofer rainbows) were stocked as 3-inch fingerlings. Those have potential to reproduce. We won’t be putting these in the Animas this year, but the feds will be stocking 50,000 5-inch rainbows – again mitigation fish.
“If someone catches one of these (Hofers), they won’t be able to look at the fish and determine if it’s (a Hofer). We test at the genetic level.”
Don Oliver, a former fishing guide who writes a fly-fishing column, said that while “whirling disease was certainly devastating,” he didn’t necessarily notice it having a major impact on rainbows, at least not here in the Animas.
“When I was guiding we caught a lot of rainbows,” he said, adding, “The Animas is a real fickle river. Some days you would catch everything in sight and other days good (guides) would come away with nothing.
“I don’t know if we’ve seen more rainbows, but I don’t know if we saw fewer rainbows, either.”
