Heat threatens fish population


— The trout population in the Yampa River may not survive this summer if the extreme drought conditions continue.

Kevin Rogers, the Division of Wildlife's aquatic biologist for Routt, Grand and Summit counties, said that a total fish kill of trout in local streams and rivers is a feasible scenario if the area's dry and hot conditions do not change.

"I'd say given our flows right now, (a fish kill) is a realistic possibility," Rogers said. "This is the real deal. It's not just people trying to glamorize things to make a good story this is a serious drought that we're in."

So far, wildlife officials and local anglers haven't noticed any fish kills.

This week's Division of Wildlife report on fishing conditions said fish in northwestern Colorado are biting good.

If summer afternoon rainstorms begin rolling in, Rogers said trout in the area may not be seriously impacted by the drought.

But if stream flow volumes and stream oxygen levels continue to decrease, and if water temperatures continue to increase, trout will have a hard time, Rogers said.

"Certainly the trout will be the first to go," he said.

One reason the drought affects trout is that trout are sensitive to water temperature and become stressed as soon as water warms to more than 70 degrees.

When rivers are low like they are now, they heat up more quickly.

Already, Rogers said he has seen temperatures in the Yampa River of 70 degrees. Typically at this time of year, water temperature is around 45 degrees.

Another problem with warmer water is that it can't hold as much oxygen as cold water. The subsequent low levels of dissolved oxygen also stress trout.

Other fish such as northern pike and suckers are able to tolerate warmer water and conditions of low oxygen, so Rogers said they should fare better this summer.

Endangered and threatened species of fish such as the Colorado pikeminnow and razorback sucker, which are found further downstream near Craig, should also be okay, he said.

"They will probably do just fine," Rogers said, "unless we start drying things up entirely."

Conditions in northwest Colorado are not nearly as serious as conditions in southern Colorado.

But that doesn't mean that Steamboat fish and aquatic ecosystems are safe.

"We had more of a snowpack than anybody else early in the year," Rogers said. "That's not to say that we're doing well."

Stream flows, which are measured as cubic feet per second (cfs), are an order of magnitude lower than normal in this region. One cubic foot of water is about 7.5 gallons.

Usually this time of year, the Yampa River flows through town at a rate of 2,100 cfs, or almost 16,000 gallons per second, according to a 92-year study.

Yesterday the flow was down to 218 cfs, or about 1,600 gallons per second, Rogers said.

Low flows affect fish in a variety of ways.

"As you get reductions in flow you obviously reduce the amount of habitat that's out there, too," Rogers said.

"Not only are you crowding the fish, which is a stressor, but you're also warming them up which is a stressor."

If large numbers of trout die this summer because of the drought conditions, Rogers said that rivers could be restocked next year, but that it would take time for populations to re-establish themselves. Recreational fishing this year would also suffer under this scenario.

One of the most serious effects would be a loss of some of the naturally reproducing populations of Brown and Rainbow trout in the area, Rogers said.

The drought could also be a blow to local fishing outfitters, said Duncan Draper, a guide for the Steamboat Fishing Company who has worked in the area for almost twenty years.

Fewer fishing trips impacts guide groups, as well as other local businesses that benefit from the lunches, gear or other items that fishermen buy.

"It's going to impact (the business) horribly," Draper said. "We're just seeing the tip of the iceberg."

Draper said he hasn't seen drought impacts on fish yet, but agreed that if the drought conditions continue, fish in the area could face serious problems around the end of July and August.


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