Colorado River from Kremmling to Dotsero Fishery management report Jon Ewert, Aquatic Biologist, Colorado Parks and Wildlife—Hot Sulphur Springs Kendall Bakich, Aquatic Biologist, Colorado Parks and Wildlife—Glenwood Springs March 2021 Introduction head and Flannelmouth suckers and Roundtail Chub are The Colorado River from Kremmling downstream to present, and small-bodied native fish such as Mottled Dotsero is one of the most popular and largest trout rivers Sculpin and Speckled Dace contribute to a prolific prey in the state. Over the course of approximately 70 river base. Aquatic invertebrates are equally abundant, with miles between the confluence with the Blue River near excellent hatches of the giant stonefly, Pteronarcys cali- Kremmling to the Eagle River at Dotsero, the Colorado fornica, occurring annually in the spring. An array of oth- flows through a stunning diversity of habitats, from deep, er stonefly species as well as mayfly, caddis, and midges rugged canyons with challenging rapids to slow, winding provide ample hatch activity most months of the year. pools and braided channels. Float fishing is very popular Colorado Parks and Wildlife (CPW) participates in the on this reach as well as whitewater rafting in certain sec- Upper Colorado Wild and Scenic Stakeholder Group tions. Public access is good throughout, with much of the (W&S SG). This stakeholder group was formed in 2007 river accessible and managed by the Bureau of Land Man- and is made up of representatives from more than 20 or- agement (BLM). ganizations ranging from government natural resource Fish populations are prolific and diverse, with Brown agencies, water providers, local governments, and non- and Rainbow Trout dominating the sport fishery, supple- profit advocacy groups. The purpose of this group is to mented by Mountain Whitefish and incidental occurrences protect and enhance the Outstandingly Remarkable Values of Brook and Cutthroat trout. Native species such as Blue- (ORVs) of the Colorado River, one of which is the excel- Figure 1. Colorado River from Kremmling to Dotsero. The locations of the four survey reaches discussed in this report are indicated by the arrows. 1 lent fishery, while also maintaining water project yield vest, with the vast majority of anglers practicing catch-and and flexibility for water users. -release angling (For more information see W&S SG An- For the past decade, CPW aquatics crews, along with nual Monitoring Reports and other documents at BLM personnel and many volunteers, mostly W&S SG www.upcowildandscenic.com). participants, have monitored fish populations on four reaches within this section of the Colorado River (Figure Methods 1). The survey reaches are 2 miles in length and evenly In the surveys discussed in this report, we used two distributed through the 70-mile section through repre- electrofishing rafts with boom-mounted electrodes work- sentative habitats, providing confidence that fish popula- ing in tandem (Figure 2). Traditional mark-recapture tion characteristics and trends observed in these reaches methodology was followed, with at least one day in be- are representative of fish population dynamics in the en- tween mark and recapture runs to allow fish to redistribute tire section. CPW uses this information to make fishery in the survey reach. Surveys are run in the spring, prior to management decisions, inform fishing regulations, and runoff, typically during the last half of April or the first make recommendations to the W&S SG. The purpose of half of May. Every effort is made to conduct the surveys this report is to describe the information that has been col- at flows of less than 2,000 cubic feet per second (CFS) at lected in these surveys to date. Results and discussion for the Kremmling USGS gage. these survey reaches will be presented in this report from Mark-recapture models are used to estimate fish popu- upstream to downstream. lation parameters. Abundance is estimated as number of Based on the information collected in these surveys, in fish per mile >6” by species. Biomass is estimated as March 2016 the CPW Commission designated 32 miles in pounds per acre (lbs/acre) of fish >6” for each species, as this river section, from the confluence of Canyon Creek at well as for all trout species combined. Quality Trout den- the mouth of Gore Canyon to the confluence of Rock sity is estimated as fish per acre >14” by species and for Creek near McCoy, as a Gold Medal fishery. all trout combined. Total trout estimates for Quality Trout In general, fisheries management on this section has density and trout biomass are reported to the W&S SG to focused on production of wild trout. However, some monitor the Fishing ORV and to compare to the Gold stocking has occurred on occasion and is discussed in the Medal Trout standard of 12 Quality Trout and 60 pounds report. The fishing harvest regulation on this section is a of trout per acre. limit of two trout of any size. The W&S SG has conduct- This report includes all surveys completed through ed river user surveys as part of their monitoring work, and 2019. Due to schedule cancellations as a result of the these surveys have documented very low rates of fish har- COVID pandemic, no surveys were conducted in 2020. Figure 2. Electrofishing raft with two netters, a rower, boom-mounted electrode, live-well, and generating equipment. 2 Radium The farthest upstream monitoring reach that CPW crews survey is the Radium station. The downstream ter- minus of this reach is the Grand County Road 11 bridge over the river at Radium (Figure 3, below). The station encompasses the Radium hot spring and the Blacktail and Sheephorn Creek confluences. This reach of river contains a wide variety of habitat including canyon-type water with large boulders, large riffles, deep pools, long runs, and braided channel. It is the most heavily used section in this Figure 4. Biomass estimates for Brown and Rainbow Trout in report by both recreational boaters and anglers. We sur- pounds per surface acre, Radium station. veyed this reach annually for four years from 2010-2013, and switched to a biennial schedule after 2013. CPW has stocked whirling disease-resistant Rainbow Trout in this reach on five occasions since 2010 (Table 1, following page). This was done on an opportunistic basis when there was excess hatchery production. The principal reason for stocking was to introduce the genetics of whirl- ing disease resistance into this section of river. The stocked fish were generally divided between the Pum- phouse and Radium boat ramps and stocked directly from Figure 5. Estimates of fish >6” per mile for Brown and Rainbow the ramps. Trout, Radium station. In general, Rainbow Trout population estimates have been highly variable (Figures 4, 5, & 6). This is most like- ly a function of the timing of our surveys, which take place immediately prior to or during Rainbow spawning activity. Our catch rates are likely affected by movement among Rainbow Trout as they prepare to spawn. On aver- age, Rainbows contribute 13.2% of total trout biomass, 10.6% of total trout >6” per mile, and 14.1% of Quality Trout. These averages are probably a more accurate re- flection of the contribution of Rainbow Trout to the total Figure 6. Density estimates of Quality Trout (>14”) in fish per trout population than individual estimates from any given surface acre, Radium station. year. Figure 3. Location of the Radium survey reach. 3 Brown Trout population estimates are more consistent, and show an upward trend since 2010. Notably, trout Brown Trout median length: abundance and biomass in 2019 were estimated at their 344 mm (13.5”) highest levels observed to date. Trout biomass and Quality Avg. body condition: 93.2 Trout density (Figures 4 & 6) have always far exceeded the minimum Gold Medal criteria of at least 60 pounds of trout biomass and 12 trout larger than 14” per surface acre. Reasons for the increase are unknown, other than the fact that this has been a relatively drought-free period with some years of extremely high runoff (2011 and 2014). Brown Trout median length: Two years, 2012 and 2018, had particularly low flows as a 351 mm (13.8”) result of poor snowpack. It is possible that the trends ob- Avg. body condition: 99.3 served in this reach are a long-term positive response to good water years, and this trend may not be sustained if a prolonged multi-year drought or extended period of low flows were to occur. The size structure of this trout population has been consistently ideal, with the median length of Brown Trout Brown Trout median length: above 13” in all surveys (Figure 7). This is exceptional for 347 mm (13.7”) Brown Trout populations in this area. Avg. body condition: 94.1 Figure 7 also identifies average body condition (relative weight) for Brown Trout. Relative weight is a descriptor of a fish’s weight relative to its length, convert- ed to a scale of 100 based on a standard weight equation. We have observed consistently excellent body condition (>90) in all our surveys to date. The fish population in this section of the Colorado Riv- er is comprised of a diversity of species of non-native and Brown Trout median length: 350 mm (13.8”) native fish including desirable sportfishes, native non- Avg. body condition: 94.9 game fishes, and undesirable invasive species. One nota- ble fish that has not historically occurred upstream of Gore Canyon but is actively expanding its range upstream in the Colorado River is the Mountain Whitefish. In our monitoring reaches, we do not typically capture enough Mountain Whitefish to generate population estimates; therefore we simply report number captured (Table 2).