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Drought stressing trout

Cliff Thompson

The thermometer won’t guarantee you’ll catch fish but it will help prevent you from fishing when the water is too warm, and it may help keep you from killing fish you don’t intend to keep.

The region-wide drought, the worst in a century, has caused record low flows in local streams and elevated water temperatures to near-lethal levels for the cold-water-loving trout – particularly in the heavily fished Eagle River, which lately has been running at 20 to 30 percent of normal.

Its temperature, meanwhile, is approaching critical levels.



“Fish feel pretty much like we do,” says Bob Nock of Eagle River Anglers in Eagle. “When you aren’t wearing waders to wade (because it’s warm), you probably shouldn’t be fishing.”

The Colorado Division of Wildlife, meanwhile, is asking anglers to voluntarily refrain from fishing where waters are too warm, says spokesman Todd Malmsbury. If you’re going to fish warm waters that are warm, he says, restrict your angling to early morning hours, when water temperatures are cooler.



Heating up

From his shop on the banks of the Eagle River, Nock has been measuring the river’s temperatures each day. In the afternoon, he says, temperatures are already approaching 65 degrees Fahrenheit – a critical temperature in the fish-angler equation. If the water is any warmer, he won’t let his guides and clients fish the river.

Nock’s fishing guides are carrying thermometers, too, and if it’s 65 degrees or warmer, they head to higher, cooler bodies of water and leave the Eagle River alone.



The Division of Wildlife’s Bill Heicher says he read 57 degrees at the fairgrounds in Eagle at 7 a.m., but by mid-afternoon the temperature had already risen to 65.

Bill Perry of Fly Fishing Outfitters in Avon also is instructing his guides to pay attention to stream temperatures. Right now he’s finding the upper Colorado is fishing well because it is cooled by releases from reservoirs.

He also is scheduling trips very early, from 5 a.m. till 2:30 p.m. so fishermen are hitting the water when it is coolest and the fishing is the best. Perry says his guides no longer are fishing the Eagle from Edwards west. In that stretch of river, he says he’s already seen some dead fish.

“The last thing we want to do is kill fish. They’re like our employees,” he says. “We’d be fine if we’d just get a couple of thunderstorms each week to cool off the river.

Anecdotal evidence suggests most fishermen are finding fishing this year is the best it has been in recent memory because the low flows have concentrated fish populations, Perry said. Anglers are catching lots of rainbow, brown, brook and occasional cutthroat trout.

Hard to breathe

Warm water puts trout in a struggle for survival.

Ironically catch-and-release angling, a practice designed to to ensure fish survival- may actually cause fish to die when it’s improperly done, says Nock. There’s evidence it isn’t always successful.

“Last year we found a number of dead fish with fingerprints on them,” said Nock. “That’s from handling fish with dry hands and removing the protective slime on their skin.”

Damaged skin creates a pathway for bacteria to attack the fish, Nock says. Anglers should wet their hands before handling fish, he adds.

Rough handling when releasing fish can also cause them to die, as can not reviving an exhausted fish properly.

Fatal sums

Warm water alone isn’t necessarily fatal to fish, it’s the accumulation of biological stress, says Eric Bergersen, a fisheries research biologist with the U.S. Geological Survey. There are instances of isolated trout surviving temperatures much warmer than 65 degrees, he says, but that is the exception, not the rule.

Warm water carries less oxygen, and it also encourages parasites, bacteria and disease.

Furunculosis, for example, attacks mostly brown trout, typically killing the largest. It’s a blood-borne disease that causes fatal bloody ulcers on fish, says Pete Walker, a fish pathologist with the Division of Wildlife. There was an outbreak of the disease in the Eagle River last summer that slowed when monsoon rains cooled the river a few degrees.

“The best thing to do is stop tormenting them,” says Walker. “On days when the water temperature is 65 or warmer, stop fishing, or go to some place where the water is colder.”

Biologists, outfitters and wildlife managers are concerned that streams are warming up this early in the summer. The warmest days typically happen in July and August, and even lower water levels are expected then.

“These low flows and higher water temperatures create potential for a major fish kill,” says Nock.

Bergersen, however doesn’t necessarily concur.

“There probably will be some fish losses here and there, but recreational fishing will not collapse. Flows are the big issue,” he says. “I wouldn’t put my rods away for the summer. Try some other locations.”

The Eagle River at Avon is flowing at less than 150 cubic feet per second, or cfs, just 30 percent of the long-term mean. That flow is more common in late summer or early autumn. Less snow than normal fell this year, causing lower-than-normal flows in local streams. Warm temperatures and less-than-normal spring rains have contributed to the low flows.

Colder is better

Even so, Nock says there’s plenty of high-elevation fishing available. He says he’s been sending clients to some of the smaller, cooler streams and higher elevation lakes where smaller fish are plentiful. To keep the fun in the game, Nock says, he fishes with extremely light rods and light lines.

“It’s just a blast,” he says. “We can catch and land 25 or more fish.”

There also are some tailwater streams released from beneath dams that are cold year-round. The Frying Pan River from beneath the dam for Reudi Reservoir, for example, typically carries a year-round temperature of 42 degrees and has a hook-educated population of lunker rainbow and brown trout. Cold water fish are most active when the water temperature is approximately 56 degrees.

One thing that will help water temperatures is the arrival of the annual summer monsoon rains that bring moisture from the gulfs of California and Mexico to the Rockies. Those rains cool water temperatures a few critical degrees.

If the waters continue to warm, the Division of Wildlife will likely enact emergency regulations on a watershed-by-watershed basis, says Bruce McCloskey, deputy director.

“We were dealt a curve ball from Mother Nature when the spring rains didn’t come,” he says.

In a worst-case scenario, if streams warm to a point where fish are at risk, anglers will be encouraged to keep what they catch. At the very least, fishing on some rivers will be restricted to the cooler, morning hours.

McCloskey says the state Wildlife Commission will be meeting July 9 in Durango to discuss emergency fishing and hunting regulations.


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