575 items found

To assess impacts of common forest management techniques on snowshoe hare density in both lodgepole pine and spruce-fir systems in Colorado.

Project Description­­

Understanding and monitoring snowshoe hare density in Colorado is important because hares comprise 70% of the diet of the state-endangered, federally threatened Canada lynx. Forest management is an important driver of snowshoe hare density, and all National Forests in Colorado are required to include management direction aimed at conservation of Canada lynx and snowshoe hare. At the same time, Forests in the Region are compelled to meet timber production and management response obligations. Such activities may depress snowshoe hare density, improve it, or have mixed effects dependent on the specific activity and the time elapsed since that activity was initiated. 

Associated Publications

Ivan, J. S. and E. Newkirk. 2019. Influence of forest management on snowshoe hare density in lodgepole and spruce-fir systems in Colorado. Pages 2-4 in Wildlife Research Report, Mammals Research Program, Colorado Division of Parks and Wildlife, Fort Collins, CO. 48 pages.

Project Status

Ongoing

Research Objectives

• Determine whether CPW biologists can effectively use exclusion devices such as weirs to prevent non-native and hybridized suckers from participating in native sucker spawning events in intermittent tributary streams.​

Project Description

Flannelmouth Sucker (Catostomus latipinnis), Bluehead Sucker (Catostomus discobolus), and Roundtail Chub (Gila robusta) are often referred to as the “three species” because the typically coexist with each other, and have similar life cycles.  Natives of the Colorado River basin, they each occupy only 45 – 55% of their historic native range in the upper Colorado River basin. All three have experienced declines due to habitat loss and invasions of non-native predatory and competitory fishes. In addition, Bluehead and Flannelmouth suckers are prone to hybridization with non-native sucker species (primarily white sucker and longnose sucker) that were unintentionally introduced to the Western Slope. The range and relative numbers of these non-native suckers have expanded in western Colorado over the last 30 years, in some areas dramatically. Continued hybridization and introgression could result in the eventual extinction of the native suckers.

Unlike native Cutthroat Trout or other coldwater species, these native suckers rely on big rivers and low elevation tributaries for much of the year. Therefore, CPW can’t effectively conserve the genetics of these species by creating isolated populations of these suckers above barriers in small streams as they do with Cutthroat Trout. Instead, CPW initiated a study to investigate the effects of excluding non-native suckers and their hybrids from an important spawning tributary of the Gunnison River.  CPW conducted a three-year study of excluding non-native and hybridized suckers from the spawning run using a picket weir and fish trap to answer this question, comparing the selected stream to another in which no fish control was attempted. To test the effectiveness of the exclusion, larval suckers were collected in both streams, and were genetically analyzed to identify the species, or hybrid composition, of each larvae. We found that picket weirs cannot always accommodate the volume of water and debris associated with spring runoff in the streams these fish spawn in, and unfortunately, there were periods of time when the weir was compromised during each year of the study. This resulted in the entry of at least some non-native suckers every year, and many of the resulting larvae had non-native genetics. Additionally, we found that the ratio of non-native to native larvae was much higher than the ratio of non-native to native adults in the exclusion stream, but these ratios matched up in the unmanipulated stream. The unmanipulated stream hosted a greater proportion of just the two native sucker species compared to the manipulated stream. This finding was concerning as it indicated that a few non-natives participating in the spawning run can have a large, disproportional effect on the population.

A new study is underway to use a better weir design – a resistance board weir – in a larger stream to exclude greater numbers of White Suckers and hybrids. Resistance board weirs can be more easily kept clean, and if overwhelmed they submerge, allowing debris to pass over. The new weir was deployed in March 2020, but precautions surrounding the Covid-19 pandemic resulted in an early termination of the work. The study resumed in 2021 and was replicated in 2022. The weir was operated during the full spawning period in 2021, and we expect that non-native suckers were unable to gain entry to the stream that year. A heavy snowpack and cool spring followed by a week of rapid warming in 2022 resulted in far-above-average flows in the creek that overwhelmed the abilities of the weir. Non-native suckers were able to access the creek for approximately half of the spawning season. Larvae collected in 2019-2023 will be genetically analyzed to determine the effectiveness of the weir.

If this study determines that non-natives can be successfully repressed to the advantage of native suckers, progeny produced in a manipulated stream would result in more pure fish in the Gunnison River. While this approach would not result in the disappearance of non-native suckers from the entire Gunnison basin, it may provide an avenue toward ensuring that the native species persist in the Gunnison Basin. If successful, this strategy could be implemented in other river basins on appropriate tributaries as well.

​Video (1:55):Western Slope Native Suckers Leaving Spawning Grounds

These Colorado River basin native Bluehead Suckers and Flannelmouth Suckers are leaving a spawning tributary in the Roubideau Creek drainage near Delta, Colorado. This video was captured in late May 2016, and PIT tag antenna data indicate that this type of scene was common for about 4 days as the tremendous numbers of fish that had ascended the stream to spawn made their exit as the water began to drop and clear up.Video (12:09): The Native ThreeColorado Parks and Wildlife's aquatic research scientists have embarked on multiple projects to protect the three fish species native to the Upper Colorado River Basin (Flannelmouth Sucker, Bluehead Sucker and Roundtail Chub). This video, ‘The Native Three’ helps tell that story. Produced by Sean Ender, Peak to Creek Films, featuring Zachary Hooley-Underwood, CPW Aquatic Research Scientist.

Complete

Research Objectives

• To investigate the influence of physical habitat conditions on the giant stonefly Pteronarcys californica density in Colorado rivers.

Project Description

Past studies show that giant stoneflies (also known as salmonflies or willow flies), serve as a primary food source for trout in Colorado rivers where they occur. They live as aquatic larvae in rivers for 3-4 years before emerging as winged adults in June to mate and die. Their large and synchronous emergence produces some of the best fishing of the year and is eagerly anticipated by many anglers. The species' high densities and large size also make them important in the flow of energy and nutrients between aquatic and riparian systems. Although giant stoneflies can exist at extremely high numbers in certain locations, the density and range of this species has decreased in some places most likely in association with changes in stream flows and physical aquatic habitat. 

CPW completed a project to determine the influence of physical stream habitat on giant stonefly density in an effort to identify limiting factors and reasons for the species' decline. To do so, CPW researchers estimated stonefly density at 16 sites on three rivers; the Gunnison, the Colorado, and the Rio Grande and measured habitat variables at each site. 

The results of this study indicated that percent fine sediment, cobble embeddedness and average cobble size were the best predictors of stonefly density. Fine sediment is defined as sand, silt and clay particles less than 2 mm in diameter. As fine sediment levels increased, stonefly density decreased. The D50 is the median cobble size and as it increased so did stonefly density. Embeddedness is the extent that cobbles are submerged or buried by silt, stonefly densities were higher in areas with low embeddedness. Fine sediment was the single best predictor of the habitat variables and it explained 45% of the variability in stonefly density while a model with all of the top three variables explained about half of overall variability (50%), so further research is necessary to identify other environmental factors that could be influencing stonefly density. To support an average density of stoneflies (compared to sites in these three Colorado Rivers), a site would have approximately 5.1% fine sediment in the riffles while maximum stonefly densities could be expected with sites that have 0-2.5% fine sediment. 

The results of this study indicate that giant stoneflies prefer riffle habitat with low fine sediment, larger sized cobble and low levels of cobble embeddedness. This information will be used to inform management and restoration activities, as well as to identify sites for giant stonefly re-introductions. By maintaining and restoring giant stonefly populations, wildlife managers can protect an important part of native aquatic ecosystems and improve river fisheries for Colorado's anglers.