Speckled Dace Rhinichthys Osculus Research Articles

Monitoring and Managing Fishes that Are Invisible and Keep Moving Around: Influences of an Invasive Species and Environmental Factors on Capture Probability

AbstractUnderstanding fish population status and trends are fundamental to effective research and management. Challenges in understanding population status include recognizing and accounting for sources of variation in capture probability () that can obscure patterns in count data and bias inferences about the population. In systems where management actions such as invasive species removals are implemented based on population triggers, errors in abundance estimation can propagate to missed management opportunities simply due to variation in , rather than actual population status. We assessed the relative importance of individual heterogeneity (species and fish size), environmental (stream discharge, temperature) and spatial variation, and interspecific interactions (density) on electrofishing for native (Speckled Dace Rhinichthys osculus, Bluehead Sucker Catostomus discobolus, Flannelmouth Sucker Catostomus latipinnis) and invasive (Brown Trout Salmo trutta, Rainbow Trout Oncorhynchus mykiss) fishes. We fit closed‐population depletion models with combinations of covariates using 6 years of data collected during invasive salmonid suppression efforts. We found that the relative importance of spatially and temporally varying environmental influences on differed between native and introduced species. Temperature was important for explaining variability in for two of three native species, and discharge had a significant influence on for both Brown Trout and Rainbow Trout. We also found that declined with increasing Brown Trout density, which would limit precision and potentially bias abundance, for two of the three native species. These results illustrate the potential importance of interspecific interactions in influencing and understanding implications of management actions, such as invasive species suppression. Our results demonstrate the need for cautious interpretation of uncalibrated catch‐per‐unit‐effort data for abundance‐triggered management actions, including those designed to promote conservation of endangered or economically valuable species.

Development and Evaluation of Habitat Suitability Criteria for Native Fishes in Three Arizona Streams

AbstractHabitat loss is a main contributor to fish fauna declines in the southwestern USA. Several studies have defined stream‐specific habitat conditions that support the growth and survival of native fish in Arizona to inform stream restoration efforts, yet general habitat use of most individual species across the region is not established. Therefore, we evaluated habitat use of four native fishes, Speckled Dace Rhinichthys osculus, Sonora Sucker Catostomus insignis, Desert Sucker Catostomus clarkii, and Longfin Dace Agosia chrysogaster, across three Arizona streams through the development of habitat suitability criteria (HSC). We developed both stream‐specific and generalized HSC for each species. Generalized HSC were calculated as the combination of stream‐specific HSC for each species. We then assessed the utility of generalized HSC through transferability among study streams. Also, past HSC studies have not considered the occurrence of nonnative species, so we tested whether the presence of nonnative fishes influenced native fish habitat use through logistic regression models. Fish and habitat data were collected along the Mogollon Rim in Arizona during the 2017 summer field season at base flow conditions. We established minimum microhabitat use for four native Arizona fish species through developing HSC. Most generalized criteria did not transfer among study streams due to variation in habitat availability and fish community structure. Logistic regression analysis showed that the presence of nonnative fishes was inversely related to the presence of two native fish species, which could have influenced habitat use of both species. The lack of transferability across streams as demonstrated in this study confirms that only HSC developed in the stream of interest or in similar undegraded streams with comparable fish communities should be used for restoration efforts. For projects to restore native fishes in streams where nonnative competitors will not dominate, the least degraded similar streams without coexisting nonnative fishes can guide restoration efforts.

Dietary specificity and overlap in endorheic river fishes: How do native and nonnative species compare?

The introduction of nonnative species is one of the most critical problems facing freshwater systems today. The rivers of the Great Basin (USA) have been particularly imperilled by nonnative species introductions and represent a valuable location to study the dietary trends of native and nonnative fishes in isolated, endorheic systems. We collected fish from 23 sites, spanning three Great Basin watersheds (Carson, Humboldt and Bear Rivers) and two elevation categories (upland and lowland). Only a single species (speckled dace Rhinichthys osculus) occurred in both elevation zones. Diet item analyses of over 500 fish stomachs indicated significant dietary overlaps between native and nonnative fishes and detailed dietary selectivity for all species. This finding, along with the low species diversity observed in the region, suggests low dietary niche diversity, which could have the potential to amplify the competitive impacts of nonnatives on native species. In upland sites, nonnative trouts were the dominant invaders, while in lowland sites warm-water nonnatives were prevalent. The management implications we recommend based on our results urge for continued monitoring of water temperature and species occurrences to predict if dietary overlaps observed in this study are likely to change in the future. SIGNIFICANCE STATEMENT: The Great Basin is an ideal endorheic region to study dietary trends in native and nonnative fishes. These trends are important in predicting competitive interactions among fishes. By looking at the diets of fishes within this region we were able to identify multiple significant overlaps among native and nonnative fishes. These results represent a baseline for future studies in the region as well as being comparable to other regions with similar invasive/native overlaps.

Identifying the source population of fish re-colonizing an arid-land stream following wildfire-induced extirpation using otolith microchemistry

Movement is necessary for re-colonization of habitats following disturbance, but methods to estimate dispersal of small-bodied fishes are limited. We evaluated the efficacy of otolith microchemistry in identifying habitat origin of longfin dace Agosia chrysogaster in the Gila River, NM, USA. Additionally, we used this method to determine the source population of speckled dace Rhinichthys osculus that re-colonized a tributary reach following wildfire-induced extirpation. We determined otolith microchemical analysis was possible after finding elevated ambient water concentrations of Mg, Mn, and Sr in the disturbed tributary both before and after wildfire relative to other source streams. These water chemistry differences allowed us to test if speckled dace were derived from downstream populations, or from those potentially persisting within refugia in the fire-affected tributary. We found that otolith signatures consistently reflected water chemistry patterns for Mn and Sr, allowing us to classify individuals to known capture locations 86% (range = 74–100%) of the time. Otolith microchemistry techniques then revealed that 88% of speckled dace that re-colonized the fire-affected tributary reach were derived from refuge populations within the tributary. Our results indicated that otolith microchemistry could be an important tool for characterizing re-colonization dynamics of fish populations residing in chemically heterogeneous stream networks.

Habitat and Fish Assemblage Associations and Current Status of Northern Leatherside ChubLepidomeda copeiin Western Wyoming

Human activities have extensively altered native fish assemblages and their habitats in the western United States. Conservation and restoration for long-term persistence of these fishes requires knowledge of their distributional patterns and life history requirements. Northern leatherside chub Lepidomeda copei (hereafter northern leatherside) is a cyprinid native to the Snake and Bear River Basins of Wyoming, Idaho, Nevada, and Utah, and it is believed to have declined in distribution relative to historical records. To address information gaps in the species' ecology and assess its status in the state, the objectives of this study were first to document the distribution (2010–2011) of northern leatherside in Wyoming and then to examine habitat factors related to the entire fish assemblage and to evaluate specific habitat associations of northern leatherside in the Bear River Basin, Wyoming. In the Bear River and Upper Snake River Basins, we documented the distribution of northern leatherside and compared it to the previously known distribution. Across the Bear River Basin, we used habitat measurements to assess abiotic features related to the distribution and abundance of northern leatherside. Northern leatherside was found across the Bear River Basin and was present in 2 streams each in the Upper Snake River and Green River Basins in Wyoming. Populations in Wyoming appear to represent the core of northern leatherside range, and our work provided a finer-scale delineation of the species' occurrence. Northern leatherside was collected from a variety of habitats, but multivariate analyses and occurrence modeling indicated it was associated with increased channel depth and depth variability, and positively associated with other native fishes (including mountain sucker Catostomus platyrhynchus, redside shiner Richardsonius balteatus, and speckled dace Rhinichthys osculus). These findings on the distribution and ecology of northern leatherside provide important new information to assist successful management and conservation efforts within Wyoming and across the species' range.

Host Fish Associations of the California Floater (Anodonta californiensis) in the Yakima River Basin, Washington

Abstract Freshwater mussels play an important role in stream ecosystems but are declining worldwide. The California floater (Anodonta californiensis, Lea 1852), formerly widespread throughout the Pacific Northwest, is listed as a federal species of concern and a candidate species for state listing in Washington (WA). Because freshwater mussels are obligate parasites on fish, conservation and restoration efforts require understanding specific host fish species. We found a previously undocumented population of A. californiensis in the upper Yakima River Basin in WA and determined its host fishes through a combination of laboratory and field studies. Two fish species, speckled dace (Rhinichthys osculus) and torrent sculpin (Cottus rhotheus), were confirmed as hosts for A. californiensis. Two fish species, three-spine stickleback (Gasterosteus aculeatus) and redside shiner (Richardsonius balteatus), were identified as hosts for A. californiensis in the laboratory portion of this study. Our results fill a sign...

Complete mitochondrial genome of the speckled dace Rhinichthys osculus, a widely distributed cyprinid minnow of western North America

The speckled dace Rhinichthys osculus (order Cypriniformes), also known as the carpita pinta, is a small cyprinid minnow native to western North America. Here, we report the sequencing of the full mitochondrial genome (mitogenome) of R. osculus from a male fish collected from the Amargosa River Canyon in eastern California, USA. The assembled mitogenome is 16 658 base pair (bp) nucleotides, and encodes 13 protein-coding genes, and includes both a 12S and a 16S rRNA, 22 tRNAs, and a 985 bp D-loop control region. Mitogenome synteny reflects that of other Ostariophysian fishes with the majority of genes and RNAs encoded on the heavy strand (H-strand) except nd6, tRNA-Gln, tRNA-Ala, tRNA-Asn, tRNA-Cys, tRNA-Tyr, tRNA-Ser, tRNA-Glu, and tRNA-Pro. The availability of this R. osculus mitochondrial genome – the first complete mitogenome within the lineage of Rhinichthys riffle daces – provides a foundation for resolving evolutionary relationships among morphologically differentiated populations of R. osculus.

An Evaluation of the Efficiency of Minnow Traps for Estimating the Abundance of Minnows in Desert Spring Systems

AbstractDesert springs are sensitive aquatic ecosystems that pose unique challenges to natural resource managers and researchers. Among the most important of these is the need to accurately quantify population parameters for resident fish, particularly when the species are of special conservation concern. We evaluated the efficiency of baited minnow traps for estimating the abundance of two at‐risk species, Foskett Speckled Dace Rhinichthys osculus ssp. and Borax Lake Chub Gila boraxobius, in desert spring systems in southeastern Oregon. We evaluated alternative sample designs using simulation and found that capture–recapture designs with four capture occasions would maximize the accuracy of estimates and minimize fish handling. We implemented the design and estimated capture and recapture probabilities using the Huggins closed‐capture estimator. Trap capture probabilities averaged 23% and 26% for Foskett Speckled Dace and Borax Lake Chub, respectively, but differed substantially among sample locations, through time, and nonlinearly with fish body size. Recapture probabilities for Foskett Speckled Dace were, on average, 1.6 times greater than (first) capture probabilities, suggesting “trap‐happy” behavior. Comparison of population estimates from the Huggins model with the commonly used Lincoln–Petersen estimator indicated that the latter underestimated Foskett Speckled Dace and Borax Lake Chub population size by 48% and by 20%, respectively. These biases were due to variability in capture and recapture probabilities. Simulation of fish monitoring that included the range of capture and recapture probabilities observed indicated that variability in capture and recapture probabilities in time negatively affected the ability to detect annual decreases by up to 20% in fish population size. Failure to account for variability in capture and recapture probabilities can lead to poor quality data and study inferences. Therefore, we recommend that fishery researchers and managers employ sample designs and estimators that can account for this variability.Received September 29, 2014; accepted January 29, 2015

Do Management Actions to Restore Rare Habitat Benefit Native Fish Conservation? Distribution of Juvenile Native Fish Among Shoreline Habitats of the Colorado River

AbstractMany management actions in aquatic ecosystems are directed at restoring or improving specific habitats to benefit fish populations. In the Grand Canyon reach of the Colorado River, experimental flow operations as part of the Glen Canyon Dam Adaptive Management Program have been designed to restore sandbars and associated backwater habitats. Backwaters can have warmer water temperatures than other habitats, and native fish, including the federally endangered humpback chub Gila cypha, are frequently observed in backwaters, leading to a common perception that this habitat is critical for juvenile native fish conservation. However, it is unknown how fish densities in backwaters compare with that in other habitats or what proportion of juvenile fish populations reside in backwaters. Here, we develop and fit multi‐species hierarchical models to estimate habitat‐specific abundances and densities of juvenile humpback chub, bluehead sucker Catostomus discobolus, flannelmouth sucker Catostomus latipinnis and speckled dace Rhinichthys osculus in a portion of the Colorado River. Densities of all four native fish were greatest in backwater habitats in 2009 and 2010. However, backwaters are rare and ephemeral habitats, so they contain only a small portion of the overall population. For example, the total abundance of juvenile humpback chub in this study was much higher in talus than in backwater habitats. Moreover, when we extrapolated relative densities based on estimates of backwater prevalence directly after a controlled flood, the majority of juvenile humpback chub were still found outside of backwaters. This suggests that the role of controlled floods in influencing native fish population trends may be limited in this section of the Colorado River. Copyright © 2014 John Wiley & Sons, Ltd.

High Diet Overlap between Native Small‐Bodied Fishes and Nonnative Fathead Minnow in the Colorado River, Grand Canyon, Arizona

AbstractRiver regulation may mediate the interactions among native and nonnative species, potentially favoring nonnative species and contributing to the decline of native populations. We examined food resource use and diet overlap among small‐bodied fishes in the Grand Canyon section of the Colorado River as a first step in evaluating potential resource competition. We compared the diets of the predominant small‐bodied fishes (native Speckled Dace Rhinichthys osculus, juvenile Flannelmouth Sucker Catostomus latipinnis, and juvenile Bluehead Sucker C. discobolus, and nonnative Fathead Minnow Pimephales promelas) across seasons at four sites downstream of Glen Canyon Dam using nonmetric multidimensional scaling and Schoener's similarity index. The diets of these fishes included diatoms, amorphous detritus, aquatic invertebrates (especially simuliid and chironomid larvae), terrestrial invertebrates, and terrestrial vegetation. Diets varied with season and were affected by high turbidity. Fish consumed more amorphous detritus and terrestrial vegetation during the summer monsoon season (July–September), when turbidity was higher. The diets of all species overlapped, but there was large variation in the degree of overlap. The diets of juvenile suckers and Fathead Minnows were most similar, while Speckled Dace had relatively distinct diets. The differences took the form of higher proportions of diatoms and amorphous detritus in the diets of Bluehead Suckers and Fathead Minnows and higher proportions of simuliids and chironomids in those of Speckled Dace. If food resources are or become limiting, diet overlap suggests that competition may occur among native and nonnative species, which could have implications for the population dynamics of these fishes and for the management of the Colorado River ecosystem in Grand Canyon.Received September 4, 2013; accepted February 11, 2014

Dietary overlap of invertivorous fishes and macroinvertebrates in the Gila River, New Mexico

The diets of stoneflies (Perlodidae) and hellgrammites (Corydalidae) from the Gila River, New Mexico, were quantified and compared to diets of three native fishes that also occupy riffle habitats along with stoneflies and hellgrammites: speckled dace (Rhinichthys osculus); longfin dace (Agosia chrysogaster); desert sucker (Catostomus clarkii). The highest overlap occurred among corydalids, desert sucker, and longfin dace, which had diets dominated by amorphous detritus. Speckled dace and perlodids consumed less amorphous detritus, with nymphs of mayflies and larval black flies dominating their respective diets. Our results suggest moderate to high overlap of resources among invertivorous fishes and invertebrates. Although we found high dietary overlap between corydalids and two fishes, it is unclear whether amorphous detritus is a limiting resource that drives competitive interactions.

Nongame Fish Species Distribution and Habitat Associations in the Snake River Basin of Southern Idaho

The distribution and abundance of game fish populations are commonly monitored closely, whereas sampling of nongame species is often neglected. We used a broad-scale salmonid sampling project both to simultaneously assess the distribution and relative abundance of nongame fish species in small streams (i.e., ≤15 m wetted width) in the Snake River basin of southern Idaho and to relate the distribution and abundance of nongame species to abiotic and biotic stream conditions in the study area. Of the 1738 reaches surveyed, 34% were dry or contained too little water to support fish, and an additional 21% had flowing water but were still absent of fish. At least one species of nongame fish was captured at 30% of the reaches surveyed, and all 18 native nongame fish species believed present in study area streams were captured. The most widely distributed species was speckled dace Rhinichthys osculus (present in 21% of surveyed reaches, excluding dry and nearly dry reaches), followed by bridgelip sucker Catostomus columbianus (19%), Paiute sculpin Cottus beldingi (15%), and redside shiner Richardsonius balteatus (13%). The species least often present (≤ 1%) were leopard dace Rhinichthys falcatus and peamouth Mylocheilus caurinus. Common carp Cyprinus carpio (captured at 3 locations) and oriental weatherfish Misgurnus anguillicaudatus (2 locations) were the only nonnative nongame species encountered. Catostomids and cyprinids generally formed a composite fish assemblage that was associated with higher stream order (i.e., farther from headwaters), lower elevation, and lower-gradient reaches where streams were wider and deeper. Stream order was the strongest loading factor for canonical correlations constructed for study reaches both above and below Shoshone Falls, suggesting that the increased abundance of catostomids and cyprinids generally occurred on a longitudinal downstream gradient. Biologists sampling game fish populations in streams should also record data on nongame species to more closely monitor their status through time.

Long‐Term Dynamics of Native and Nonnative Fishes in the San Juan River, New Mexico and Utah, under a Partially Managed Flow Regime

AbstractNonnative fishes and flow alteration are primary threats to native fish persistence in lotic systems. We used several flow regime attributes and fish sampling data obtained from the San Juan River, New Mexico and Utah, during 1993–2010 to evaluate the potential use of flow manipulations to increase recruitment of native fishes that must cope with nonnative species. During this period, discharge in the river was partially manipulated by reservoir releases that augmented naturally high spring flows in this snowmelt‐driven system. An information theoretic approach was used to rank candidate models that predicted species densities based upon selected combinations of flow attributes and abundances of nonnative species. Autumn density of age‐0 fishes in secondary channels was the main response variable. The main predictor variables included flow attributes associated with interannual variation in daily discharge and water temperature; densities of nonnative competitors; and catch rates of a numerically dominant nonnative predator (the channel catfish Ictalurus punctatus). Top‐ranked models for native species included positive associations with small‐bodied nonnative fishes and negative associations with the abundance of channel catfish adults. Densities of native speckled dace Rhinichthys osculus and flannelmouth suckers Catostomus latipinnis increased with mean spring discharge, but the density of native bluehead suckers C. discobolus did not. With the exception of juvenile channel catfish, the top candidate models predicting densities of nonnative fishes all included the duration of low summer flows. These results confirmed findings from a previous study that demonstrated different responses of native and nonnative fishes to seasonal flows; the present study also revealed that densities of all fishes were generally lower in years with greater abundance of adult channel catfish. Regression analysis indicated that seasonal flow manipulations and suppression of nonnative predator populations could be effective management tools to restore and maintain the native fish community.

The Influences of Body Size, Habitat Quality, and Competition on the Movement and Survival of Juvenile Coho Salmon during the Early Stages of Stream Recolonization

AbstractUnderstanding the factors influencing the success of juvenile Pacific salmon Oncorhynchus spp. in newly colonized habitats is essential to their recovery in large areas across the West Coast of the United States and Canada. We studied biotic and abiotic factors associated with survival during the early stages of colonization and population establishment of juvenile coho salmon O. kisutch in Rock Creek, a tributary of the upper Cedar River in the Lake Washington basin of Puget Sound, Washington. The stream was occupied by resident fishes (e.g., rainbow trout O. mykiss, cutthroat trout O. clarkii, speckled dace Rhinichthys osculus, and several sculpins Cottus spp.), but adult coho salmon and other anadromous fishes had been excluded by a dam from 1901 until fish ladder installation in 2003. We defined logistic regression models and used an information‐theoretic approach to predict apparent survival with various combinations of individual fish condition, location competition, and local habitat quality. The best‐approximating models included measures of brood year, body size, habitat, and migration timing. Survival was positively associated with body size and habitat quality and negatively associated with competition. Survival from late summer to smolt migration varied among years (mean ± SD = 27 ± 11%) and was significantly higher within Rock Creek (73 ± 11%) than during seaward migration in the Cedar River and Lake Washington (38 ± 14%). Juvenile coho salmon established a population and outnumbered resident salmonid species by 40% in the lower 2 km of Rock Creek within 5 years of colonization. Overall, the results revealed the linkage between the colonization success of juvenile coho salmon and the biotic features and habitat quality in a newly accessible environment during the stream‐rearing phase of their life history.

Nonnative Fish Control in the Colorado River in Grand Canyon, Arizona: An Effective Program or Serendipitous Timing?

AbstractThe federally endangered humpback chub Gila cypha in the Colorado River within Grand Canyon is currently the focus of a multiyear program of ecosystem‐level experimentation designed to improve native fish survival and promote population recovery as part of the Glen Canyon Dam Adaptive Management Program. A key element of this experiment was a 4‐year effort to remove nonnative fishes from critical humpback chub habitat, thereby reducing potentially negative interactions between native and nonnative fishes. Over 36,500 fish from 15 species were captured in the mechanical removal reach during 2003–2006. The majority (64%) of the catch consisted of nonnative fish, including rainbow trout Oncorhynchus mykiss (19,020), fathead minnow Pimephales promelas (2,569), common carp Cyprinus carpio (802), and brown trout Salmo trutta (479). Native fish (13,268) constituted 36% of the total catch and included flannelmouth suckers Catostomus latipinnis (7,347), humpback chub (2,606), bluehead suckers Catostomus discobolus (2,243), and speckled dace Rhinichthys osculus (1,072). The contribution of rainbow trout to the overall species composition fell steadily throughout the study period from a high of approximately 90% in January 2003 to less than 10% in August 2006. Overall, the catch of nonnative fish exceeded 95% in January 2003 and fell to less than 50% after July 2005. Our results suggest that removal efforts were successful in rapidly shifting the fish community from one dominated numerically by nonnative species to one dominated by native species. Additionally, increases in juvenile native fish abundance within the removal reach suggest that removal efforts may have promoted greater survival and recruitment. However, drought‐induced increases in river water temperature and a systemwide decrease in rainbow trout abundance concurrent with our experiment made it difficult to determine the cause of the apparent increase in juvenile native fish survival and recruitment. Experimental efforts continue and may be able to distinguish among these factors and to better inform future management actions.

Overriding Effects of Species‐Specific Turbidity Thresholds on Hoop‐Net Catch Rates of Native Fishes in the Little Colorado River, Arizona

AbstractI 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 relative to the turbidity thresholds predetermined much of the catchability of fish. Catch rates were highest in a high‐catch zone consisting of the lowermost turbidities, which ranged up to the start of a transition zone for each species (humpback chub, ≤54 NTU; speckled dace, ≤29 NTU; flannelmouth sucker, ≤81 NTU; bluehead sucker, ≤26 NTU), and the secondary effects of temperature were only detectable in this zone. Catch rates within the transition zone decreased at higher turbidities up to the thresholds and thereafter remained consistently low at all higher turbidities within this low‐catch zone. The effects of the turbidity thresholds on catch rates decreased for larger fish of all species. Theoretically, the effects of turbidity reflect a behavioral switch by native fishes from relying primarily on structural cover (e.g., hoop nets) to using turbidity as cover to reduce the predation risk as turbidity increases from below to above the thresholds. Moreover, turbidities within the low‐catch zone could be totally incapacitating the fishes' visual capabilities such that fish perceive these turbidity levels as unlimited visual cover. The turbidity threshold concept probably applies to the hoop‐net catch rates of other fishes in other riverine systems.

Irrigation Canals as Sink Habitat for Trout and Other Fishes in a Wyoming Drainage

AbstractIrrigation canals can be a major source of mortality for fish in the Rocky Mountain region. Our study looked at how fish were affected by the irrigation canal system in the Smiths Fork, a tributary to the Bear River in western Wyoming. There are two native species of conservation concern in the Smiths Fork drainage: Bonneville cutthroat trout Oncorhynchus clarkii utah and northern leatherside chub Lepidomeda copei. Our objectives were to determine the relative abundance of each species within the canals and the fate of trout (Bonneville cutthroat trout and brown trout Salmo trutta) that enter canals. During the summer of 2003 we sampled 30 sites within the Covey Canal system, which is the largest canal system withdrawing water from the Smiths Fork. Because fish were observed to accumulate at certain spots in the canal system, we developed a sampling scheme that incorporated both random sample sites and sites known to attract fish. We estimated that between 6,300 and 10,400 fish encompassing 10 species were entrained in this canal system. The two most abundant species were speckled dace Rhinichthys osculus (29% of all fish) and mountain sucker Catostomus platyrhynchus (37% of all fish). Bonneville cutthroat trout and northern leatherside chub each comprised 2% of the total entrained fish. We implanted 30 Bonneville cutthroat trout and 13 brown trout with radio transmitters to determine whether entrained trout could leave the canal system when water levels were reduced in late summer. We found that 77% of the transmitter‐implanted fish died within the canals, indicating that this system functions as sink habitat for Bonneville cutthroat trout and brown trout. Based on this mortality rate, we estimated that 120 Bonneville cutthroat trout (95% confidence interval, 75‐165) and 299 brown trout (280‐317) perished in the Covey Canal system during the summer of 2003.

Stream Fish Responses to Grazing Exclosures

AbstractEight paired reaches of northeastern Oregon streams were selected such that one reach was an established livestock exclosure and a neighboring, geomorphologically similar reach was open to grazing. Exclosures varied in length from 123 to 436 m. Teams of snorkelers recorded fish species and size‐groups in the exclosure and grazed reaches simultaneously so that diurnal changes in fish behavior did not confound results. Observed densities of age‐0 redband trout Oncorhynchus mykiss in pools, corrected for snorkeler range of vision, were significantly different (P < 10−9), increasing by an average of 2.5‐fold in exclosed reaches. Conversely, warmwater fishes (dominated by speckled dace Rhinichthys osculus) were negatively related to exclosures (P < 0.001). Densities of age‐0 warmwater fish and age‐0 O. mykiss were uncorrelated (P = 0.18). No first‐order interactions existed among exclosure–control treatment, stream, and pool temperature variables in either age‐0 analysis. Combined juvenile and adult O. mykiss results indicated significant interactions between several streams and temperature and only a marginal effect (P = 0.05) of exclosure. No significant exclosure effect existed on combined juvenile and adult warmwater fish (P > 0.90). The greater density of age‐0 O. mykiss in exclosures was attributed to the potential food supply and cover due to increases in undercut banks, instream bank vegetation, width : depth ratio, and several riparian vegetation variables. Bioenergetic and scale arguments are presented that are consistent with the failure to detect a parallel effect with juvenile and adult O. mykiss. A marginally significant (P = 0.04) mean drop in pool water temperature of 0.7°C in exclosures was observed, but continual temperature monitoring indicated no significant difference (P > 0.50) between reaches in 7‐d means of daily maxima or minima. These results are promising with respect to improvement of salmonid habitat through prevention of grazing, but the exclosures are too small and infrequent to be effective at the population or basin‐wide level.

Comparison of Upper Thermal Tolerances of Native and Nonnative Fish Species in Arizona

AbstractWe used a lethal thermal method to estimate the upper thermal tolerances of 11 native and 7 nonnative fish species found throughout southern Arizona. Fish were acclimated to 25°C and 30°C. For all species tested, an increase in acclimation temperature resulted in a higher thermal tolerance value. Among the species acclimated to 25°C, desert pupfish Cyprinodon macularius, western mosquitofish Gambusia affinis, and Gila topminnow Poeciliopsis occidentalis were most tolerant to high temperature. Speckled dace Rhinichthys osculus, spikedace Meda fulgida, and loach minnow R. cobitis were least tolerant. Many native species demonstrated a limited ability to extend their upper temperature tolerances via acclimation. Our data suggest that several native species may be sensitive to increasing annual and large daily temperature fluctuations in Arizona's streams and rivers. Although southwestern native fishes were previously believed to be tolerant to high temperature due to their evolution in desert environments, this study suggests that many of these fishes are less tolerant than previously thought. In addition, many fishes introduced from the eastern United States had higher temperature tolerances than some of the native desert species tested. Increases in stream temperatures in Arizona could reduce the habitat available for native fishes and therefore may favor those nonnative species with higher thermal tolerances.

Random versus Fixed‐Site Sampling When Monitoring Relative Abundance of Fishes in Headwater Streams of the Upper Colorado River Basin

AbstractNative 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. When one‐pass backpack electrofishing was used, detection of 10% or 25% changes in CPUE (fish/100 m) at 60% statistical power required 50–1,000 randomly sampled reaches among species regardless of sampling design. However, use of a fixed‐site sampling design with 25–50 reaches greatly enhanced the ability to detect changes in CPUE. The addition of seining did not appreciably reduce required effort. When detection of 25–50% changes in CPUE of native and nonnative fishes is acceptable, we recommend establishment of 25–50 fixed reaches sampled by one‐pass electrofishing in Muddy Creek. Because Muddy Creek has habitat and fish assemblages characteristic of other headwater streams in the UCRB, our results are likely to apply to many other streams in the basin.