Gunnison’s rainbow numbers up, but still struggling

Each fall, researchers from the Colorado Division of Wildlife sample trout populations in the Gunnison River. While brown trout continue to dominate the river, recent surveys indicate rainbow trout numbers are on the increase.


Each fall, Colorado Division of Wildlife aquatics biologist Dan Kowalski leads a team of researchers into the Gunnison Gorge and Pleasure Park sections of the Gunnison River to determine the effectiveness of stocking whirling disease-resistant rainbow trout.

Survey data from 2010 indicate the parasite-resistant rainbows are reproducing and young rainbows again are surviving in the Gunnison River.

Initially, the overall survival of stocked fish has been low, especially during high water years and in areas where high numbers of brown trout are found.

Last fall’s sampling revealed multiple year classes of wild rainbows in Ute Park with an estimated population of 16 pounds per acre and 205 per mile.

By comparison, brown trout dominate this part of the river, with 344 pounds per acre and 10,342 fish per mile.

Yes, 10,342 fish per mile. Think about that the next time you are fishing the Gunnison and go home skunked.

While the brown trout biomass increased 9.2 percent from 2009 with a corresponding 43.4 percent increase in density, it’s promising to note the rainbow trout biomass is up 45.5 percent with a 95.2 percent jump in density.

Kowalski said this is great news for the rainbow population.

This year, Kowalski said he wants to stock 1-inch long half-Hofer, half-wild rainbow fingerlings as part of his ongoing study and research.

Similar-sized fish were stocked last summer in the river near Chukar Trail, but the entire stocking was lost during the Aug. 19 flash flood.

In addition to weather events, dam operators may impact trout populations by failing to maintain minimum flows, raising or lowering river volumes too quickly, and allowing high flows during the brown spawn (mid-October to May) and the rainbow spawn (mid-April to July).


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