This spring, water groups are allocating reservoir spill water to help native fish species on the Lower Dolores River.
Unlike sport fish introduced from outside sources, native species have been swimming local rivers for an estimated 2 million years. But the past few decades, they have become not only low on the food chain, but low on the water chain after water is prioritized for irrigation, industry, drinking water and recreation.
Native fish species found on the Lower Dolores River include the flannelmouth sucker, bluehead sucker and roundtail chub.
This year, after a winter of below average precipitation, water officials will be releasing a trickle of spill water a little early from the cold bottom of the McPhee Reservoir before the spring rafting spill in an effort to keep water temperatures low during warm spring weather and prevent native fish from spawning too soon.
Although water officials expect the reservoir to fill this spring, the excess spill is currently expected to provide a limited 10 whitewater boating days on the river below the dam.
The problem is when you get a really rapid rise in temperature very quickly, and then these fish start to mature, there are eggs, and they start to get in spawn mode, said Jim White, an aquatic biologist with Colorado Parks and Wildlife. Then the spill comes along and that water temperature just plummets. That can be very hard on the newly hatched larval fish.
Recognizing that a threatened or endangered species designation for the native fish could bring government intervention and regulation of the river, whitewater boating organizations have agreed to sacrifice some spill water for the fish, said Mike Preston, manager of the Dolores Water Conservancy District.
The boating community is really good about saying part of our boating experience is the health of the river. So were ready to cooperate in terms of providing some water for the ecology, even if affects the number of boating days in the interest of a healthy river, Preston said.
White acknowledged temperature is not the only spawning cue, but he hopes the release will mimic a more natural hydrograph and provoke a spawn after the spill.
In wet years, water is released before the spill regardless to prevent the reservoir from overflowing. What makes this year unique, is that the early release is tailored specifically for the native fish.
While it wont be known this year if the early release to cool spring waters helped the native fish, White said officials will be able to know how river temperatures are affected using satellite monitoring.
We will be able to see if releasing those increments kept the water from getting too warm too early, he said. Well be able to evaluate that in real time.
If more young native fish are found in next years fish surveys, then biologists will then be able to surmise that this years spawn was more successful.
Fish surveys indicate the native species are making a comeback. Electro-fishing and net-capture techniques in 2011 yielded 35 percent native fish on the river, White said, up from 9 percent in 2007.
However, samples are dominated by the non-native and predatory small mouth bass, which make up 57 percent of fish netted.
The fish release represents a new level of cooperation between the numerous organizations who have interest in the river and its precious waters.
Were pretty excited to see some interesting opportunities in progress, White said.
Reach Reid Wright at [email protected].
