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Floodplains are presumed to be important rearing habitat for the endangered razorback sucker (Xyrauchen texanus). To help recover this endemic Colorado River Basin species, the Upper Colorado River Endangered Fish Recovery Program implemented a floodplain acquisition and enhancement program. Levee removal was initiated in 1996 as one component of this floodplain restoration program. The goal of the Levee Removal Study was to evaluate the system responses to levee removal and make specific recommendations concerning the value of floodplain/river reconnecting for endangered species (specifically razorback sucker) recovery.
Four groups of larval razorback sucker, an endangered fish, were exposed to selenium-laden zooplankton and survival, growth, and whole-body residues were measured. Studies were conducted with 5, 10, 24, and 28-day-old larvae fed zooplankton collected from six sites adjacent to the Green River, Utah. Water where zooplankton were collected had selenium concentrations ranging from <0.4 to 78 microg/L, and concentrations in zooplankton ranged from 2.3 to 91 microg/g dry weight. Static renewal tests were conducted for 20 to 25 days using reference water with selenium concentrations of <1.1 microg/L. In all studies, 80-100% mortality occurred in 15-20 days. In the 28-day-old larvae, fish weight was significantly reduced...
Larval and juvenile Colorado pikeminnow (Ptychocheilus lucius) use shallow, low-velocity, channel-margin areas (backwaters) as nursery habitats. It is hypothesized that within-day flow fluctuations caused by hydropower operations can directly affect the suitability of such habitats by altering water temperature and habitat geometry. Despite the importance of backwaters to juvenile fishes, there is a lack of established approaches for modelling how river management affects these habitats. Here, we describe a physical habitat model that predicts the effects of mainstem flow variation on backwater temperature, geometry and invertebrate availability. We specifically modelled these effects on habitat in a portion of...
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Populations of the endangered razorback sucker (Xyrauchen texanus) in the middle Green River have declined since closure of Flaming Gorge Dam in 1962. The apparent cause for the decline is a lack of successful recruitment. Recruitment failure has been attributed to habitat alteration and competition and predation by exotic fishes on early life stages of razorback sucker. This study was conducted to evaluate two of the potential reproductive bottlenecks that might limit recruitment of razorback sucker in the Green River Drainage; (1) reduced larvae production due to sediment deposition on spawning areas, and (2) reduced survival of larvae or juveniles due to lack of timely access to food-rich backwater and floodplain...
Benthic macroinvertebrates from four habitat types (river channel, ephemeral side channel, river backwater, and seasonally inundated wetland) were examined from the Green River at the Ouray National Wildlife Refuge, Uintah County, UT, June-August 1991. For major taxa (Nematoda, Oligochaeta, Diptera: Ceratopogonidea, and Chironomidae) were quantified. Chuster analysis of densities showed that habitat types with comparable flow conditions were the most similar. Highest to lowest overall benthic invertebrate densities of the four habitats were as follows: ephemeral side channel, river backwater, seasonally inundated wetland, and river channel. Nematodes were the most abundant taxon in all habitat types and sample dates...
We evaluated the role of major tributary streams for endangered fish recovery using a matrix approach based on quantitative information. However, the need for ranking tributaries for direct and indirect contributions (i.e., assignment of high, medium or low importance) required a more subjective approach. Some streams differed in actual and potential importance because barriers deny fish access to suitable habitat. We have not assigned relative importance to the different types of contributions; to a large extent that may involve policy issues better addressed by the Recovery Program.
The role of biotic interactions in structuring freshwater invertebrate communities has been extensively studied but with mixed results. For example, fish effects on invertebrates are most pronounced in pelagic and soft-sediment benthic habitats that lack structural complexity, yet appear insignificant in benthic rubble habitats. Backwaters of the Green River, Utah, are shallow, structurally simple, quiet-water embayments adjacent to the river. These habitats form in middle to late summer and are colonized by benthic and epibenthic invertebrates that produce standing crops significantly higher than the river. Backwaters are also utilized by a large number of fish species. We used cages to determine if selective exclusion...
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Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to...
We compared beaver (Castor canadensis) foraging patterns on Fremont cottonwood (Populus deltoides subsp. wislizenii) saplings and the probability of saplings being cut on a 10 km reach of the flow-regulated Green River and a 8.6 km reach of the free-flowing Yampa River in northwestern Colorado. We measured the abundance and density of cottonwood on each reach and followed the fates of individually marked saplings in three patches of cottonwood on the Yampa River and two patches on the Green River. Two natural floods on the Yampa River and one controlled flood on the Green River between May 1998 and November 1999 allowed us to assess the effect of flooding on beaver herbivory. Independent of beaver herbivory, flow...
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Currently, little is known about the native fish assemblages present in the Green River drainage of southwestern Wyoming. Of particular interest are the bluehead sucker (BHS), flannelmouth sucker (FMS), and the roundtail chub (RTC). Bluehead sucker, FMS, and RTC have declined in Wyoming and throughout their native ranges. The Natural Heritage Program assigns BHS the global ranking of G4 suggesting its existence to be abundant and globally secure, although it may be quite rare in parts of its range and is thus the element of long-term concern (Fertig and Beauvais 1999). The Natural Heritage Program assigns FMS the global ranking of G3/G4 suggesting its existence to be uncertain. It is uncommon but seems...
Floodplain plant-herbivore-hydroperiod interactions have received little attention despite their potential as determinants of floodplain structure and functioning. We used five types of exclosures to differentially exclude small-, medium-, and large-sized mammals from accessing Fremont cottonwood (Populus deltoides Marshall subsp. wizlizenii (Watson) Eckenwalder) seedlings and saplings growing naturally on four landform types at an alluvial reach on each of two rivers, the Green and Yampa, in Colorado and Utah. The two study reaches differed primarily as a result of flow regulation on the Green River, which began in 1962. Landforms were a rarely flooded portion of the alluvial plain, geomorphically active slow-...
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Canyon riparian zone vegetation is vulnerable to effects of upstream river regulation. We studied box elder (Acer negundo) dominated canyon riparian forests intensively on the Green and Yampa rivers in Dinosaur National Monument, Colorado, and extensively in four other major rivers of the upper Colorado River Basin to determine the effects of river regulation on riparian tree establishment patterns. We: 1) aged individuals to determine if establishment was correlated with high annual peak flows, 2) mapped cohorts to determine if the areal extent of post-regulation cohorts was reduced on regulated compared to unregulated river reaches, and 3) measured the floodplain position of cohorts in regulated and unregulated...
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The Colorado River Basin provides habitat for 14 native fish, including four endangered species protected under the Federal Endangered Species Act of 1973 - Colorado pikeminnow (Ptychocheilus lucius), razorback sucker (Xyrauchen texanus), bonytail (Gila elegans), and humpback chub (Gila cypha). These endangered fish species once thrived in the Colorado River system, but water-resource development, including the building of numerous diversion dams and several large reservoirs, and the introduction of nonnative fish, resulted in large reductions in the numbers and range of the four species. Knowledge of sediment dynamics in river reaches important to specifc life-stages of the endangered fishes is critical to understanding...
Despite successful reproduction by razorback suckers (Xyrauchen texanus) in the middle Green River, recruitment beyond the larval stage has not been recently observed. Bonytail (Gila elegans) are essentially extirpated in the wild and nearly all bonytail present in the Green River are hatchery-stocked fish. Floodplain wetlands may provide important rearing habitat for both larval razorback sucker and bonytail. However, survival of razorback suckers in restored floodplain habitat has not been observed since 1997, even when larvae were introduced directly into floodplain sites. Large nonnative fish populations in floodplain habitats have likely suppressed survival. The recent drought eliminated, or reset, nonnative...
In northwestern Colorado, flow regulation on the Green River has created a transitional plant community that features encroachment by upland vegetation into cottonwood (Populus fremontii)-dominated, riparian forest on topographically high floodplain sites and reduced cottonwood regeneration on low floodplain sites. To assess how these changes might have affected small mammal distributions, in 1994 and 1995 we live-trapped during periods surrounding spring flooding at 3 sites: above and below the confluence of the regulated Green River and at the ecologically similar, but unregulated, Yampa River (reference site). More species were captured at the most regulated site along the Green River above its confluence, with...
Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to...
During the 20th Century the flow of most rivers in the United States was regulated by diversions and dams, with major impacts on riparian forests. Few unregulated rivers remain to provide baseline information for assessing these impacts. We characterized patterns in riparian plant communities along chronosequences on the unregulated Yampa River and the regulated Green River in northwestern Colorado, examining patterns in plant species diversity in relation to the ages of floodplain terraces. On both rivers, mean plant species richness in cottonwood (Populus deltoides Marshall subsp. wislizenzii (Watson) Eckenwalder) dominated riparian forests declined by more than 50% from young sites (<20 years) to old upland terraces...
Analysis of field data and development and application of a dynamic model indicate that the processes that control the number and distribution of age-0 Colorado pikeminnow in the middle Green River are poorly understood. Colorado pikeminnow are a federally endangered species endemic to the Colorado River basin that utilize backwaters during their larval stage. The present agency-mandated field sampling program for backwater habitats may be inadequate because it takes place at a time when the model predicts that most larval fish have drifted beyond the study area. The model predicts that water releases from Flaming Gorge Dam have a large potential effect on larval drift, because high releases at the time of drift...
Floodplain restoration is an important element of the Upper Colorado River Endangered Fish Recovery Program. Floodplain restoration was initiated in 1996 by lowering natural and manmade levees that were preventing natural floodplain function by limiting the frequency and duration of river-floodplain connection.
map background search result map search result map Summary of Fluvial Sediment Collected at Selected Sites on the Gunnison River in Colorado and the Green and Duchesne Rivers in Utah, Water Years 2005-2008 Processes of Tamarix invasion and floodplain development along the lower Green River, Utah. Effects of river regulation on riparian box elder (Acer Negundo) forests in Canyons of the upper Colorado River Basin, USA Green River Watershed Native Non-Game Fish Species Research: Phase II Effects of river regulation on riparian box elder (Acer Negundo) forests in Canyons of the upper Colorado River Basin, USA Processes of Tamarix invasion and floodplain development along the lower Green River, Utah. Green River Watershed Native Non-Game Fish Species Research: Phase II Summary of Fluvial Sediment Collected at Selected Sites on the Gunnison River in Colorado and the Green and Duchesne Rivers in Utah, Water Years 2005-2008