Fish habitat in the upper Dolores River basin is at risk from overall warmer weather and longer, more intense droughts, according to a long-term climate study recently released by Trout Unlimited.
“Climate Change and the Upper Dolores Watershed, a Cold Water Fishery Adaptive Management Strategy,” is an extensive three-year analysis done in cooperation with the Mountain Studies Institute in Silverton.
The study used 72 climate models to tease out potential impacts to 46 trout streams in the basin from the town of Dolores to Lizard Head Pass up to the year 2100.
“We know there will be change, the question the study addresses is what kind of change can we expect, the approximate timing, and what are the impacts,” said Duncan Rose, director of the Dolores River Anglers chapter of Trout Unlimited.
When climate scientists ran the models over time, they pointed toward a “feast and famine” scenario, where wet periods with higher temperatures are followed by longer, more intense droughts.
According to the study, between 1949 and 2012, the upper Dolores watershed experienced wet periods with increasingly higher temperatures, followed by dry periods that were longer and more intense.
“We see that pattern developing where each drought gets more intense, and the wetter periods have higher temperatures, which causes increased evaporation and overall net loss of moisture,” Rose said.
If cyclical drought conditions were like 2002, the worst in recent years, and lasted for many years, the result could mean an average of 44 percent reduction in stream flows throughout the upper basin in 50-70 years, according to the study. Low stream flows contribute to higher water temperatures, which if reach above 63 degrees, are detrimental to trout species.
“Trout have survived these cycles for millennia, but the climate conditions may be more intense than what we have seen, so we’re going to have more challenges, particularly on the lower elevation streams,” Rose said.
The study is intended to aid current and future managers of Colorado Parks and Wildlife and the San Juan National Forest in sustaining good trout habitat in the basin.
For example, higher elevation streams will be less impacted by the climate predictions. Lower trout streams may be more or less a lost cause, with many perennial streams potentially becoming intermittent or drying up completely.
“That leaves the middle elevation band of streams, where mitigation and stream rehabilitation will do the most good,” Rose said. “It’s an adaptive management model, where we don’t rush in, take it a step at a time and invest limited resources with what climate pattern emerges.”
Protecting trout streams from higher temperatures and lower flows means improving shade, installing instream rocks and trees to create pools where fish can find refuge in lower flows and hot conditions. Streams like Roaring Fork, Scotch Creek, Kilpacker, Burnett, and higher-up stretches of the Dolores Main stem, plus others, would likely benefit the most from habitat improvement in the future.
More regulations may by on the horizon, as a result of the study’s projections, for example, lower bag limits, catch-and-release only rules, barbless hooks, and even rotating some streams into non-fishing status for a year to allow recovery.
The climate models indicate there will likely be a reduction in the 295 miles of trout streams in the upper Dolores Basin in the next 50 to 100 years. More of the fishing spots will be concentrated in the higher elevations, which would result in more people fishing in a smaller area.
“There will be more competition for fewer fish, but the good news it will not happen overnight,” Rose said. “We have time to adapt, as long as we are aware of the potential impacts.”
This summer, the Dolores chapter of Trout Unlimited will be installing eight temperature gages on various streams and rivers at different elevations to start monitoring changes and trends.
The Dolores River climate change study cost about $20,000 with $15,000 paid for by the Colorado Water Conservation Board. Other groups, including TU, Southwestern Water Conservation District and the Montezuma Land Conservancy contributed funds as well.
For a power point summary of the study go to bit.ly/Troutunlimited
jmimiaga@the-journal.com
