CPW asks anglers to avoid certain hours on the Yampa as river temps continue to rise
At 7 p.m. Thursday, the Yampa River’s temperature was 72 degrees at a spot in the Chuck Lewis Wildlife Area south of Steamboat. That’s about 15 degrees higher than the typical average.
With the current abnormally warm water temperatures, higher ambient air temperatures and lower river water levels that continue to drop, fish in the Yampa River Basin are stressed. Colorado Parks and Wildlife is now asking anglers to avoid fishing the river during the hotter part of the day.
Colorado Parks and Wildlife Aquatic Biologist Bill Atkinson recommends fishing before 11 a.m. or noon and after 7 p.m., especially on sunny days.
“The big take home is with the water temperatures rising with these extremely warm days, it is stressing the trout populations,” said Atkinson, who has worked in the CPW aquatics division for 22 years. “It would be beneficial if people would focus their fishing time during the cooler parts of the day.”
Atkinson said when river water temperatures rise, the metabolic rate of fish also rises so they require more oxygen. Yet the warmer the water, the less oxygen that water can hold. Fish are ectotherms, or cold-blooded animals, so the regulation of body temperature depends on external sources, he said. Atkinson said for a temperature increase of approximately 18 degrees, metabolic rates of fish can roughly double. He compares that heat stress on fish to when humans run a marathon.
“It is harder for fish to exchange oxygen from water at warm temps, and it is additional stress for fish to move out of the way of people in the river or when being hooked,” Atkinson said.
The stressed fish focus on pumping enough oxygen and can become slow, lethargic and reduce feeding. Over time, those stressed fish lose weight.
Atkinson’s chief level of concern is for the native mountain whitefish, which are strained by higher water temperatures and low-flow conditions.
“Of native species, mountain whitefish numbers in the Yampa basin already are low, and they are definitely very susceptible to stresses related to water temperature,” Atkinson said.
The adult population density of trout species in the Yampa River through Steamboat decreased by 45% from 2015 to 2019, according to periodic CPW sampling. With a combination of the tougher environmental conditions and the substantial increase in recreational activities, including fishing during the COVID-19 pandemic, conditions “are not favorable for trout and whitefish populations.”
Atkinson said providing the fish some stress relief this time of year aids the long-term stability of the fish population, because the fish build up energy reserves during the spring, summer and fall to be able to live through the lean times of winter.
During this warmer, dryer year, local CPW officials are also keeping a watchful eye on fish stocking plans. The agency stocks area reservoirs and the Yampa River with young fish, but some local reservoirs that are mainly for agricultural use may be drained extremely low by the end of the summer. So, CPW may not stock those agricultural use lakes this year and focus more on stocking recreational use lakes, Atkinson said.
“We are closely monitoring conditions in the river and lakes, and we adjust fish stocking rates based on existing and predicted conditions,” he said. “As time goes on and we look at what the rivers are doing, we will possibly modify stocking. Right now, things don’t look good.”
To reach Suzie Romig, call 970-871-4205 or email sromig@SteamboatPilot.com.
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