REVIVING RAINBOW TROUT IN COLORADO WITH A CLIP OF A FIN
Colorado fish lovers hunched over buckets at a hatchery, fingers numb inside soaked, black-wool mittens, scooping up shiny rainbow trout that have developed an ability to fight off the aquatic equivalent of plague that has ravaged Western rivers for four
These volunteers snipped off the left pelvic fin from the belly of each trout. Then they plopped them back into tanks, 20,000 fish in two intense work days last month. Rainbow trout are nonnative fish, introduced during Colorado’s 19th century mining boom for human food and fun. They became stars in the state’s multibillion-dollar fishing industry because fishermen find them dynamic and relatively catchable.
But whirling disease hit rainbow trout so hard they no longer can reproduce widely on their own.
The fin snipping to mark rainbows of a newly discovered resilient subgroup will allow tracking when Colorado Parks and Wildlife biologists release them into the recovering Arkansas River this spring.
It is the latest step as CPW runs with a scientific breakthrough that could lead to the defeat of whirling disease. Like rainbow trout, the disease is imported. A parasite invader hitched a ride to Pennsylvania from Europe in 1958 on a frozen fillet and has been attacking the soft cartilage of fingerling rainbows ever since, causing them to grow into deformed, c-shaped juveniles.
They swim in circles and die of starvation or exhaustion.
Whirling disease decimated fisheries around Colorado and the West, leaving rainbow trout in need of life support. Fishing for them in Colorado since whirling disease took hold in the 1990s has been possible only thanks to state government intervention. Colorado spends $3.8 million a year to stock 2,800 lakes and reservoirs and 9,500 miles of streams with 5.8 million rainbows.
Now this new breed of rainbows could make a comeback.
“We’re trying to re-create a naturally reproducing, self-sustaining rainbow trout population,” CPW aquatic biologist Mike Atwood said as he supervised the Trout Unlimited volunteers at the hatchery west of Salida.
Four years ago, a researcher investigating rainbow genetics spotted an isolated group at the bottom of a rocky chasm in the Black Canyon of the Gunnison River — rainbow trout that seemed able to withstand whirling disease. State biologists verified the immunity and began a genetic analysis.
Focusing so much on saving a single nonnative fish species has appeared, in the eyes of some purists, dispropor- tionate. Crossbreeding, perceived as genetic engineering, raises concerns about manipulating natural processes. But ever since European settlers arrived, fish life in the West has faced constant intrusions as people harness rivers for economic purposes. River ecosystems now are so scrambled — by dams that destroy seasonal fluctu-
ating flows, by pollution, by managing of species — that restoration is seen as increasingly difficult.
“We just don’t have the wherewithal to restore all the rivers to native fish, even if people had the desire,” Trout Unlimited’s regional director David Nickum said. “Most of our rivers have changed to be nonnative fisheries. That’s what they’re going to be. Let’s make them the best wild trout fisheries we can, native or not.”
“This is a practical matter: Do you want to have rainbow trout in some of the rivers? Or just brown trout? If you want to have rainbow trout as part of the picture in Colorado,” he said, “you pretty much have to look at being open to a little bit of animal husbandry.”
The latest human demand on Colorado’s rivers and streams comes from a booming, lucrative recreation industry, which includes fishing valued by state statisticians in 2015 at $1.9 billion.
While CPW biologists also are working at saving imperiled native fish species, such as the greenback cutthroat trout, ensuring abundant non-native rainbow trout has emerged as a priority. The agency relies on revenues from hunting and fishing licenses because state lawmakers have rejected broader funding for wildlife, though a bill that gained momentum in the state house last week could inject new support from taxpayers.
“Our agency is about trying to provide good fishing and hunting opportunities for our constituents. Wild rainbow trout are a big part of providing those opportunities,” said Montrose-based CPW aquatic biologist Eric Gardunio, who runs an artificial spawning operation on the banks of the Gunnison River to supply tens of thousands of the resilient rainbow trout.
“We stocked all these non-native fish (a century ago),” Gardunio said. “Although they provided good sport fisheries, they really harmed our native fish here in Colorado. Now, we cannot really manage for those native fish on the main stems of our rivers. So we manage for brown trout and rainbow trout. And then these impacts (from whirling disease) came up.”
“All through the West, we are dealing with highly altered ecosystems. We spend a lot of time trying to get fish back. We’re trying to undo sins of our forefathers. … We’re trying to encourage further adaptation in order to get these rainbow trout back.”
The whirling disease parasite that had infected fisheries in Pennsylvania and other Eastern states reached Colorado in 1980. It took hold inside this fish hatchery along the Arkansas River with devastating effects. Whirling disease parasites spread with river water into hatchery pipes and tanks, contaminating state fish-breeding operations. When rainbow trout were distributed statewide for stocking, so was whirling disease. The result was the near-total ruin of rainbow trout. Whirling disease also threatens other fish, including the native greenback cutthroats.
State aquatic crews have been laboring, with limited success, to re-establish rainbow trout. They rebuilt the hatchery so that it no longer relies on river water that carried whirling disease parasites, along with contaminants from mining. The hatchery now uses water pumped up from wells, depending on agricultural irrigation needs that in Colorado are given priority.
Colorado’s fight against whirling disease also included crossbreeding rainbow survivors with a Hofer strain from Europe that had evolved with partial immunity to the parasites, which live in worms on river bottoms and must penetrate fish in order to reproduce.
That’s what led aquatics researcher Eric Fetherman to the Black Canyon of the Gunnison River.
Fetherman expected to find that the surviving rainbow trout he observed carried Hofer genetics. But the CPW genetic analysis conducted in 2013 showed no sign. The results indicated this isolated group of rainbows likely had developed an immunity. They live along a 2-mile stretch of the Gunnison in relatively cool, low-sediment pools below the Crystal Dam.
“They are able to reproduce naturally,” Fetherman said. “It is probably an adaptation that happened over time — not something that was natural in our fish here in Colorado. It was a bit of a surprise.”
The discovery prompted CPW leaders to launch their breeding blitz, starting at a tent camp on banks of the Gunnison where crews net hundreds of the resilient rainbows. This artificial spawning entails squeezing out milt from male fish and extracting tens of thousands of eggs from females, then mixing these and hauling it all in coolers to hatcheries where fry and fingerlings are nurtured in captivity.
Last year, state biologists tossed some of their captive-bred rainbows into the Arkansas River. While acid metals contamination from inactive mountainside mines still impairs headwaters, state data show, the river flows around Salida are diluted enough that brown trout are multiplying. The biologists used an electro-fishing survey method to check up on those resilient rainbows, marked for tracking. They determined that the fish were surviving.
“They looked healthy,” CPW’S Atwood said. “If we saw these fish weren’t surviving, we’d probably explore other options. This is something brand new. It is early. It is going to take years of effort. Hopefully they will reproduce in the river and we’ll be able to document that. … We feel optimistic.”
Whirling disease may be stay in Colorado, depending on the extent to which parasites can find host fish. But now, rainbow trout may be able to stay, too, he said, “so that we don’t have to keep stocking them year after year.”