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We measured water temperature at 87 sites in six streams in two different years (1998 and 1999) to test for association with the occurrence of Lahontan cutthroat trout Oncorhynchus clarki henshawi. Because laboratory studies suggest that Lahontan cutthroat trout begin to show signs of acute stress at warm (>22°C) temperatures, we focused on the maximum daily temperature. The maximum daily temperature associated with the occurrence of Lahontan cutthroat trout ranged from 18.9°C to 28.5°C. Occurrence was more likely at colder (<26°C) sites. In two streams, the maximum daily temperature associated with the occurrence of these trout was relatively cool (≤20°C). In these streams, the response to temperature may...
We investigated the effects of constructed instream structures on movements and demographics of bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta in the upstream portion of Muddy Creek, an isolated headwater stream system in the upper Colorado River basin of Wyoming. Our objectives were to (1) evaluate upstream and downstream movements of these three native species past a small dam built to divert irrigation water from the stream and a barrier constructed to prevent upstream movements of nonnative salmonids and (2) describe population characteristics in stream segments created by these structures. Our results indicated that upstream and downstream movements...
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There is little information on the winter features of salmonid habitats associated with constructed instream structures to provide guidance when planning habitat improvement projects. We assessed winter habitat features for trout of the genera Oncorhynchus and Salvelinus in pools associated with two types of instream structures constructed on a low-gradient reach of a mountain stream in western Wyoming with a mean wetted width of 6.4 m. Pool habitat was affected by temporal variability in ice formations from fall into winter. As surface ice and snow accumulated with the progression of winter, variation in ice formations was less frequent and winter habitat conditions became more stable. However, groundwater inflow...
Studies of the whirling disease epizootic in the upper Colorado River drainage have suggested that Windy Gap Reservoir is a source of the fish-infective actinospore of Myxobolus cerebralis. We divided the reservoir into four quadrants (12 zones) and conducted a core-sampling study to determine the spatial dynamics of actinospore production within the reservoir from late June to early November 1998. Core samples of reservoir substrate containing aquatic oligochaetes were collected, held for 24 h in filtered lake water, and then examined microscopically for actinospore production. Actinospores were produced from core samples taken in every quadrant, but the samples from one quadrant gave the overall highest estimates...
Because of its relatively natural hydrograph, the Yampa River, Colorado, is considered the crown jewel of native fish habitat in the upper basin of the Colorado River and has supported a relatively intact native fish assemblage. Nonnative fishes are thought to pose the greatest threat to native fishes in this system. Removal programs for nonnative northern pike Esox lucius and channel catfish Ictalurus punctatus have highlighted managers' perception of the threat posed by each species. Recent expansion of nonnative smallmouth bass Micropterus dolomieu in the Yampa River attracted an avid angling clientele but also coincided with a precipitous decline in native fishes, necessitating a rigorous assessment of the relative...
A repatriation program to conserve critically imperiled razorback sucker Xyrauchen texanus, an endemic fish of the Colorado River basin in western North America, was initiated in 1990. The species, once widespread and abundant, now is extirpated from most of its range because of human-induced factors. Natural recruitment to wild populations rangewide is largely precluded by nonnative predation. The largest remaining wild population occurs in Lake Mohave, Arizona and Nevada, but its numbers have declined dramatically over the past decade, such that the genetic legacy of the species may soon be lost. As part of a cooperative repatriation program, more than 440,000 naturally produced razorback sucker larvae were harvested...
Rainbow trout Oncorhynchus mykiss stocked into Flaming Gorge Reservoir, Utah– Wyoming, are thought to be in poor condition and to rarely overwinter. In 2001–2002, we evaluated factors that affect the growth and abundance of rainbow trout, both temporally and spatially, based on a series of field measurements and growth experiments. Based on our field measurements, the growth and condition of rainbow trout in Flaming Gorge Reservoir actually parallel those of rainbow trout of various strains in other systems, and some rainbow trout overwinter as many as 3 years in the reservoir. Overall, rainbow trout appear to be spatially limited by physical factors (e.g., temperature) during only a few isolated times of the...
The Colorado pikeminnow Ptychocheilus lucius is a federally endangered species restricted to the Colorado River. Dexter National Fish Hatchery and Technology Center, Dexter, New Mexico, maintains three separate captive stocks of the Colorado pikeminnow: 1974YC (Yampa River), 1981YC (Green?Colorado rivers), and 1991YC (Colorado River). We surveyed mitochondrial DNA diversity in these three stocks (879 base pairs [bp]; ND-4L and ND-4 genes; N = 30) and in museum specimens collected from 1890 to 1976 (450 bp; ND-4; N = 11). All individuals had the same haplotype except for a 1-bp variant detected in 2 of the 12 fish from 1981YC. The low variation is postulated to be the result of a post-Pleistocene bottleneck in the...
We investigated electrofishing catchability (q) for brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss in the Colorado River, Grand Canyon National Park, Arizona, over a range of fish densities, water temperatures, turbidities, conductivities, shoreline types, and seasons. The covariance of q with rainbow trout density strongly resembled random distributions, thereby suggesting no relationship between q and rainbow trout density. The catchability of rainbow trout was greater in turbid water (?480 nephelometric turbidity units [NTU]) than in clear water (?10 NTU), although lower water temperature may have contributed to this effect. The catchability of rainbow trout was greatest over sand?silt shorelines....
Native fishes of the upper Colorado River basin (UCRB) have declined in distribution and abundance due to habitat degradation and interactions with nonnative fishes. Consequently, monitoring populations of both native and nonnative fishes is important for conservation of native species. We used data collected from Muddy Creek, Wyoming (2003–2004), to compare sample size estimates using a random and a fixed-site sampling design to monitor changes in catch per unit effort (CPUE) of native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, roundtail chub Gila robusta, and speckled dace Rhinichthys osculus, as well as nonnative creek chub Semotilus atromaculatus and white suckers C. commersonii....
Most subspecies of cutthroat trout Oncorhynchus clarkii are imperiled or extinct due to the combined effects of habitat degradation and interactions with exotic species. To quantify abundance and vital rates and evaluate trends, we selected a large population of Bonneville cutthroat trout O. clarkii utah from the Logan River of northern Utah, a river characterized by high-quality and connected habitat. Over a 5-year period, we completed a comprehensive population assessment, including depletion-based abundance estimates and a mark–recapture study (1,050 tagged fish) of site fidelity, growth, and survival. Population density exceeded 1,500 cutthroat trout/km at high-elevation sites; this is substantially higher...
Understanding the population dynamics of native and nonnative fishes is critical for guiding and evaluating management activities, but obtaining information on population dynamics is often dependent on identifying structures that provide precise estimates of age. We examined age estimation using various hard structures for native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta, and nonnative white suckers C. commersonii, creek chub Semotilus atromaculatus, white sucker3bluehead sucker hybrids, and white sucker 3 flannelmouth sucker hybrids in a small headwater stream of the upper Colorado River basin (UCRB) in Wyoming. We evaluated between-reader precision...
The New Zealand mud snail (NZMS) Potamopyrgus antipodarum is rapidly invading North American freshwaters, leading to speculation that native fisheries, especially those involving trout, will be negatively impacted. To assess whether trout would consume NZMSs and could assimilate nutrients from them, we conducted a laboratory 15N tracer study, a laboratory feeding study, and bioenergetics modeling with rainbow trout Oncorhynchus mykiss; we also evaluated 5 years of diet and condition data describing rainbow trout and brown trout Salmo trutta collected from a river colonized by NZMSs. The 15N tracer study showed that rainbow trout consumed and to a lesser extent assimilated NZMSs. Rainbow trout fed 15N� labeled NZMSs...
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We captured rainbow trout Oncorhynchus mykiss in the Colorado River below Glen Canyon Dam, Arizona, between 1995 and 1997 to develop baseline data for a modified health assessment index (mHAI) and to determine relationships among mHAI, parasite burden, relative condition, mesenteric fat index, and diet. We also examined effects of a simulated flood on these variables during 1996. There were no significant effects of the flood on variables measured in the fish. Total stomach volume increased during spring and summer following the flood and reflected an expected trend. Health of fish, based on the mHAI, remained good throughout the study but declined with increasing burden of the nematode Truttaedacnitis truttae and...
The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture?recapture-based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid-1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age-2 and older fish are age dependent but apparently...
Standard weight (Ws) equations have been used extensively to examine body condition in sport fishes. However, development of these equations for nongame fishes has only recently been emphasized. We used the regression-line-percentile technique to develop standard weight equations for four rare desert fishes: flannelmouth sucker Catostomus latipinnis, razorback sucker Xyrauchen texanus, roundtail chub Gila robusta, and humpback chub G. cypha. The Ws equation for flannelmouth suckers of 100?690 mm total length (TL) was developed from 17 populations: log10Ws = ?5.180 + 3.068 log10TL. The Ws equation for razorback suckers of 110?885 mm TL was developed from 12 populations: log10Ws = ?4.886 + 2.985 log10TL. The Ws equation...
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Warmer water, changes in stream flow, and the increasing frequency and intensity of other disturbances are among the factors associated with climate change that are likely to impact native trout populations in the western USA. We examined how three of these factors?increased summer temperatures, uncharacteristic winter flooding, and increased wildfires?are likely to affect broad-scale population persistence among three subspecies of cutthroat trout Oncorhynchus clarkii. Our results suggest that as much as 73% of the habitat currently occupied by Bonneville cutthroat trout O. c. utah, 65% of that occupied by westslope cutthroat trout O. c. lewisi, and 29% of that occupied by Colorado River cutthroat trout O. c. pleuriticus...


    map background search result map search result map Winter ice processes and pool habitat associated with two types of constructed instream structures Health Assessment, Associated Metrics, and Nematode Parasitism of Rainbow Trout in the Colorado River below Glen Canyon Dam, Arizona Potential consequences of climate change to persistence of cutthroat trout populations Health Assessment, Associated Metrics, and Nematode Parasitism of Rainbow Trout in the Colorado River below Glen Canyon Dam, Arizona Winter ice processes and pool habitat associated with two types of constructed instream structures Potential consequences of climate change to persistence of cutthroat trout populations