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The population of endangered razorback suckers Xyrauchen texanus in the middle Green River (upper Colorado River basin) has declined during the last 40 years. The apparent cause for this decline is a lack of successful recruitment. This study used radiotelemetry to evaluate the ability of hatchery-reared razorback suckers to locate spawning areas where wild fish congregate during the ascending hydrographic limb of the snowmelt runoff. Hatchery-reared razorback suckers appeared to show similar reproductive behavior to wild fish. Both wild and hatchery-reared fish were found near the middle Green River spawning area between 1 and 25 May 2000. Hatchery fish occupied the same areas on the spawning site as wild fish,...
Estimates of the age and growth of roundtail chub Gila robusta were made by analyzing thin cross sections of sagittal otoliths from 280 specimens collected in the upper Verde River, Arizona, from January 1997 to December 1999. Marginal increment analysis indicated that a single annulus completed formation between January and May. The use of otoliths to age roundtail chub was further validated using otoliths of known-age, hatchery-reared fish for which (upon examination) the number of annuli agreed 100% of the time with the true age of the fish. In addition, daily increments were observed on sagittal otoliths of age-0 roundtail chub and, when counted, agreed with the true age of fish 70% of the time; daily ring counts...
For populations of cutthroat trout Oncorhynchus clarkii, isolation in headwater streams may provide protection from invasion by nonnative species but also may enhance a population's vulnerability to extirpation. We assessed the risk of extirpation for eight Colorado River cutthroat trout O. clarkii pleuriticus populations isolated above water diversion structures in the North Fork Little Snake River drainage, Wyoming. The populations had been isolated for 25–44 years, occupied headwater streams that ranged from 850 to 6,100 m in length, and had adult populations that were estimated to range from 12 to 506 fish. Adult population sizes were compared with published occurrence models to identify populations that may...
The population of endangered razorback suckers Xyrauchen texanus in the middle Green River (upper Colorado River basin) has declined during the last 40 years. The apparent cause for this decline is a lack of successful recruitment. This study used radiotelemetry to evaluate the ability of hatchery-reared razorback suckers to locate spawning areas where wild fish congregate during the ascending hydrographic limb of the snowmelt runoff. Hatchery-reared razorback suckers appeared to show similar reproductive behavior to wild fish. Both wild and hatchery-reared fish were found near the middle Green River spawning area between 1 and 25 May 2000. Hatchery fish occupied the same areas on the spawning site as wild fish,...
Rainbow trout Oncorhynchus mykiss are one of the most widely stocked salmonids worldwide, often based on the assumption that they will effectively utilize abundant invertebrate food resources. We evaluated the potential for feeding morphology to affect prey selection by rainbow trout using a combination of laboratory feeding experiments and field observations in Flaming Gorge Reservoir, Utah–Wyoming. For rainbow trout collected from the reservoir, inter–gill raker spacing averaged 1.09 mm and there was low variation among fish overall (SD = 0.28). Ninety-seven percent of all zooplankton observed in the diets of rainbow trout collected in the reservoir were larger than the interraker spacing, while only 29% of...
Digestive tracts of 34 preserved adult razorback suckers Xyrauchen texanus from Lake Mohave, Arizona-Nevada, were examined. Contents were dominated by planktonic crustaceans, diatoms, filamentous algae, and detritus. The species is equipped for and apparently pursues a planktivorous habit, but benthic materials in the diet indicate bottom feeding also occurs. Published in Transactions of the American Fisheries Society, volume 116, issue 1, on pages 117 - 119, in 1987.
Estimates of the age and growth of roundtail chub Gila robusta were made by analyzing thin cross sections of sagittal otoliths from 280 specimens collected in the upper Verde River, Arizona, from January 1997 to December 1999. Marginal increment analysis indicated that a single annulus completed formation between January and May. The use of otoliths to age roundtail chub was further validated using otoliths of known-age, hatchery-reared fish for which (upon examination) the number of annuli agreed 100% of the time with the true age of the fish. In addition, daily increments were observed on sagittal otoliths of age-0 roundtail chub and, when counted, agreed with the true age of fish 70% of the time; daily ring counts...
Abstract.?We investigated distribution and dispersal patterns of subadult and adult Colorado squawfish Ptychocheilus lucius (recently renamed the Colorado pikeminnow) throughout their range in the upper Colorado River. Annual, river-wide, capture?recapture data were used to document movements during a 5-year period (1991?1995). Average total length of Colorado squawfish progressively increased upstream: juveniles and subadults occurred almost exclusively in the lowermost 105 km of the 298-km study area, whereas most adults were concentrated in the uppermost 98 km. This was most pronounced early in the study and less so later due to the effect of two or three strong year-classes that dispersed through the system....
A single stocking of 611 wild flannelmouth suckers Catostomus latipinnis in 1976 represented the first successful reintroduction of a native fish in the lower Colorado River. Flannelmouth suckers ranging in age from young of the year to 24 years were captured during 1999?2001; their population was estimated as at least 2,286 (95% confidence interval, 1,847?2,998). Recruitment appeared sporadic, consisting of consecutive years of low recruitment (<10%) supplemented by a stronger (31%) year-class. Historically, this native fish was rare and was believed extirpated from the lower river by 1975, but it now reproduces naturally in a reach dramatically altered by water development. This successful reintroduction indicates...
Predation experiments, field studies, and individual-based-model (IBM) simulations revealed factors that affected the survival and recruitment of early life stages of endangered Colorado pikeminnow Ptychocheilus lucius in the Green River basin, Utah and Colorado. Small-bodied, nonnative red shiners Cyprinella lutrensis attacked Colorado pikeminnow larvae an average of once per minute, and predation success approached 30% in laboratory aquaria. Attack rate was also high in mesocosm experiments; turbidity and alternative prey reduced predation success. Distributions of hatching dates derived from otolith daily increment analysis showed that large cohorts of Colorado pikeminnow larvae that hatched in the Green River...
Myxobolus cerebralis, the causative agent of salmonid whirling disease, has been implicated in year-class losses of rainbow trout Oncorhynchus mykiss in several rivers in Colorado. The hypothesis that other factors, such as elevated water temperature, bacterial pathogens, and gas supersaturation, are contributing to these year-class losses was tested in a laboratory setting. Fingerling rainbow trout were exposed to all combinations of these stressors for 6 months. Mortality and morbidity were evaluated for each of the test groups using analysis of variance (ANOVA). Mortality was significantly affected by exposure to M. cerebralis (P = 0.0002) and elevated water temperature (P = 0.0002). Morbidity was significantly...
Multiple age-classes of Bonneville cutthroat trout Oncorhynchus clarkii utah throughout two Rocky Mountain watersheds were influenced by interactions among geomorphology, land use, activity by beavers Castor canadensis, and drought. Age-0 trout were present in a limited portion of the watersheds, and their distribution became increasingly restricted as drought conditions developed over a 3-year period. The Coal Creek watershed (including Huff Creek) produced the most age-0 trout in the first 2 years of the drought, lacked beaver activity, and was affected by land use, suggesting that spawning habitat was determined by geomorphology rather than land use or beaver activity. However, the high abundance of age-0 cutthroat...
Translocation is a key strategy for conserving native subspecies of cutthroat trout Oncorhynchus clarkii that have declined markedly throughout their native range. Previous research showed that successful translocations of cutthroat trout in high-elevation southern Rocky Mountain streams were more likely in streams with warm summer water temperature and led to the hypothesis that cold summer temperatures govern translocation success by limiting recruitment. We tested this by measuring the density and size of age-0 cutthroat trout (greenback cutthroat trout O. c. stomias and Colorado River cutthroat trout O. c. pleuriticus) in six headwater streams in north-central Colorado that varied in thermal characteristics....
Juveniles (age 0-1) of three endangered Colorado River fishes were subjected to a gradient of total dissolved solids (TDS) to determine the concentrations that they preferred or avoided. Preferred and avoided TDS concentrations, respectively, for juveniles of each species were: Colorado squawfish Ptychocheilus lucius, 560-1,150 mg/liter and greater than 4,400 mg/liter; humpback chub Gila cypha, 1,000-2,500 mg/liter and greater than 5,100 mg/liter; and bonytail Gila elegans, 4,100-4,700 mg/liter and less than 560 mg/liter or greater than 6,600 mg/liter. Colorado squawfish and humpback chubs selected TDS concentrations that were similar to those in waters they now inhabit, but bonytails selected concentrations four...
The endangered razorback sucker Xyrauchen texanus is endemic to the Colorado River system in western North America and is threatened with extinction because of limited recruitment. To assist in management and recovery efforts, we developed methods for the cryopreservation of sperm, evaluated the influence of various factors on motility of thawed sperm, and examined the effect on fertilization of cooling rate and the addition of caffeine. Sperm samples cryopreserved with 10% methanol (MeOH) had significantly higher postthaw motility than did samples preserved with 5% or 20% MeOH or with 5% or 10% dimethyl sulfoxide, N,N-dimethylacetamide, glycerol, propylene glycol, or ethylene glycol. Sperm samples cryopreserved...
Many management agencies use hydroacoustic surveys to estimate pelagic prey fish abundance and population trends. It would be desirable to simultaneously assess piscivore population size and predation demand. However, multiple sources of variation in target strength complicate the target strength?fish size relationship, impairing managers' ability to distinguish the echoes of predators and prey. This uncertainty may substantially bias population size estimates, especially for piscivores that are greatly outnumbered by other species. We used an in situ estimate of target strength variance combined with fish length-frequency distributions to estimate the distribution of target strengths for prey-sized kokanee Oncorhynchus...
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I examined the effects of turbidity, discharge, and temperature on hoop-net catch rates of native humpback chub Gila cypha, speckled dace Rhinichthys osculus, flannelmouth suckers Catostomus latipinnis, and bluehead suckers C. discobolus in the Little Colorado River, Arizona. Results indicated that native fish catch rates were primarily influenced by whether turbidity levels were below or above species-specific thresholds of approximately 545 nephelometric turbidity units (NTU) for humpback chub, 221 NTU for speckled dace, 846 NTU for flannelmouth suckers, and 70 NTU for bluehead suckers. The effects of discharge were negligible, but discharge did dictate the turbidity level. Turbidity levels at hoop-net deployment...
Native salmonids are increasingly restricted to upstream habitats that may be too cold to sustain recruitment, and recruitment limitation owing to cold temperatures is a main hypothesis to explain translocation failures of native cutthroat trout Oncorhynchus clarkii in high-elevation streams in the southern Rocky Mountains. We subjected Colorado River cutthroat trout O. c. pleuriticus fry to one of three temperature regimes (cold, intermediate, or warm), which averaged 7.0, 8.5, and 10.08C during the warmest summer month, in each of 2 years. The regimes mimicked those of natural streams where translocated fish had died out or produced populations of cutthroat trout of low or high abundance. The mean fry survival...
Growth and adult survival rates were estimated for the endangered Colorado squawfish Ptychocheilus lucius inhabiting the upper Colorado River by using data from fish captured during 1990–1995. Mean annual growth rates of fish aged 3–6 years ranged from 32.2 (age 6) to 82.0 (age 3) mm/year. Growth rates for older fish were highest for fish 400–449 mm total length, TL, (42.7 mm/year) and declined to 19.8 mm/year for fish 500–549 mm TL. Fish 550 mm and longer grew an average 9.5 mm/year. Survival rates for fish 550 mm and longer were estimated by comparing measured size distributions with simulated stable age and size distributions; these ranged from 0.83–0.87, with the best fit at 0.85. Though lack of historical...
Twenty-nine species of fishes were collected in the middle and upper Colorado River basins in 1967-1973. The native suckers, Catostomus latipinnis and C. discobolus, were the dominant species in the study area. Introduced species outnumbered native species 19 to 10. The introduced Ictalurus punctatus and Notropis lutrensis were abundant throughout most of the upper basin. The abundance of introduced species has increased steadily since 1900 as has the introductions of new species. Four endemic species, Ptychocheilus lucius, Gila elegans, Gila cypha, and Xyrauchen texanus, are considered endangered. These rare forms reproduce in the lower Yampa River, Desolation Canyon of middle Green River, and the lower Green River...


map background search result map search result map Overriding Effects of Species-Specific Turbidity Thresholds on Hoop-Net Catch Rates of Native Fishes in the Little Colorado River, Arizona Overriding Effects of Species-Specific Turbidity Thresholds on Hoop-Net Catch Rates of Native Fishes in the Little Colorado River, Arizona