Q. Describe the conditions of the Yampa River and other local streams. How do river flows and temperatures compare to previous years? How serious are conditions for fish right now?
A. We are experiencing extremely low flows right now in rivers across the state. The Yampa and its tributaries are carrying about one-tenth of the volume they normally do this time of year, and we are setting record lows every day.
With less volume, water temperatures can increase much more rapidly. While the tributaries are still fairly cool, the mainstem Yampa through town is already warmer than 70 degrees in the afternoon and evenings. Typically, we don't see those temperatures until August. Given that flows will continue to drop, and a full summer still lies ahead, I am very concerned about the trout fishery through town.
Q. Why are fish susceptible to low flows and high temperatures? What does increased water temperature do to a fish's metabolism and other body functions?
A. Not only do low flows reduce the amount of habitat that is available for fish to live in, high temperatures act as an additional stressor. Because fish are cold blooded, increasing temperatures increases their metabolism and consequently, oxygen consumption.
Unfortunately, warm water cannot hold as much dissolved oxygen as cold water can, so low oxygen levels act as another stressor. Bodily functions and growth are optimized over a narrow range of temperatures that coincides with the temperature regime that a fish evolved in. For trout, that temperature is around 60 degrees. When temperatures exceed 70 degrees, trout become stressed and are more vulnerable to a variety of diseases. Some will stop eating entirely and actually lose weight during warm spells.
While they can tolerate short periods of warm water, protracted episodes cause problems.
Q. Which types of fish are most susceptible to low river flows and high water temperatures? Are some species of trout more vulnerable that others? Are some sizes of trout more vulnerable than others? Why?
A. Yes, fish that evolved in warmer temperature regimes will be better able to withstand higher temperatures. Northern pike for instance are commonly referred to as "coolwater" fish. Their bodily functions are optimized around 70 degrees and will do just fine in the Yampa until water temperatures exceed 80 degrees.
Of the trout species, brown and rainbow trout can tolerate warmer waters than brook and cutthroat trout again, merely a reflection of where these fish evolved.
Larger fish tend to be more tolerant of low oxygen levels that come with higher temperatures than smaller fish, and they also occupy the best positions in the stream (near cool water sources) forcing small fish into marginal habitats.
Q. If there were a total trout kill in the Yampa, how long would it take to restore the fish populations? Does the Division of Wildlife have any options such as buying more water to prevent this large of a fish kill from happening?
A. If we do sustain a major trout die off in the Yampa, the Division of Wildlife would restock the river with fingerling rainbow and brown trout next spring. Some larger fish might be introduced to provide some immediate recreation, but it would take several years for the fingerlings to mature. Unfortunately, the mountain whitefish would take longer to rebound, as their populations would have to recover naturally. The Division of Wildlife has been exploring options to secure water, but unlike other rivers in the state, the Yampa does not have large storage projects on it. Although some water is stored in Stagecoach Reservoir and the headwaters, it is designated for other uses.
Q. Would you recommend that anglers give the Yampa River a rest at some point this summer? Under what river conditions would you give that recommendation and why would it be important to not fish for a period of time?
A. At this point, water temperatures are still favorable in the mornings (60 degrees). As temperatures rise throughout the day, it will become increasingly difficult to catch fish as they become stressed by the warming water. If evening temperatures exceed 74 degrees, then one should seek fishing opportunities elsewhere. If you do catch fish in town, it is important to minimize the additional stress inflicted by angling, as stress is cumulative. Use heavy tippets so that fish can be landed quickly, and try to keep them in the water as much as possible. A net will also help speed the release process.
If the drought persists and water temperatures continue to increase, the Division of Wildlife may implement fishing closures on waters across the state to try and protect trout populations pray for rain!