Flannelmouth Sucker Research Articles

Use of a Molecular Assay to Detect Predation on an Endangered Fish Species

AbstractMastication, digestion, and rapid evacuation rates make visual identification of larval fish remains in the digestive tracts of predatory fishes problematic. Recent advances in molecular technology, however, have increased the likelihood of identifying remnants of partially digested larval prey, thereby enabling assessment of predator impacts on local populations. Conducting controlled laboratory experiments, we evaluated the utility of quantitative polymerase chain reaction (qPCR) for identification of Razorback Sucker Xyrauchen texanus larvae in the digestive tracts of Green Sunfish Lepomis cyanellus and Western Mosquitofish Gambusia affinis. Primers and a probe were developed to amplify a fragment from Razorback Sucker mtDNA. Tests using a suite of potential predators and prey indicated that these primers and probes amplified only mtDNA from Razorback Sucker and Flannelmouth Sucker Catostomus latipinnis, an allopatric and allochronic species in the lower Colorado River. Amplification with primers for Razorback Sucker‐specific DNA fragments identified Razorback Sucker DNA in the digestive tracts of 87.5% of Green Sunfish and Western Mosquitofish at 2 h postfeeding. After 12 h, DNA fragments were identified in 75.0% of Green Sunfish but in only 28.6% of Western Mosquitofish. No Razorback Sucker DNA was found in 24‐h postfeeding samples, though it was detected in 12.5% of both Western Mosquitofish and Green Sunfish at 48 h postingestion. The sensitivity of qPCR provides a useful tool for extending the time period in which Razorback Sucker larvae can be identified beyond that of traditional visual analyses of stomach contents.

Long-Term Monitoring of an Endangered Desert Fish and Factors Influencing Population Dynamics

AbstractThe lower perennial corridor of the Little Colorado River in Grand Canyon, Arizona, is numerically dominated by endemic desert fishes and therefore significant for conservation of these species. From 2000 to 2012, the U.S. Fish and Wildlife Service conducted monitoring of native fishes in the Little Colorado River near its confluence with the Colorado River. The primary focus of these efforts was to estimate the spring and fall abundance of native fishes, especially the federally endangered humpback chub Gila cypha. Because humpback chub in Grand Canyon are influenced by operations of Glen Canyon Dam, our efforts provide managers of the Glen Canyon Dam Adaptive Management Program with abundance estimates and trends of humpback chub in the Little Colorado River, the most important tributary in Grand Canyon for spawning and production of this species. From 2001 to 2006, the spring abundance estimates of humpback chub ≥150 and ≥200 mm remained relatively low (≤3,419 and ≤2,002 fish, respectively), thereafter significantly increasing to highs of 8,083 and 6,250, respectively, by spring 2010. Also from 2000 to 2006, the fall abundance estimates of humpback chub were substantially below those abundances estimated after 2006. In addition, flannelmouth sucker Catostomus latipinnis and bluehead sucker Catostomus discobolus showed post-2006 increases in relative abundance, suggesting a systemwide event occurred that was beneficial to native fishes. Most of the increases of humpback chub occurred during the spring season in the reaches of the Little Colorado River between 5 and 13.57 km upstream from the confluence. Successful production of age 0 year classes of humpback chub may be partially driven by hydrograph dynamics of the Little Colorado River, whereas water temperatures and predation pressures in the mainstem Colorado River likely influence survivorship of native fishes into subadult and adult life stages.

Longer food chains and crowded niche space: effects of multiple invaders on desert stream food web structure

AbstractTributaries of the Colorado River Basin, historically home to a complex of endemic omnivores collectively referred to as the ‘three species’; flannelmouth sucker (Catostomus latipinnis), bluehead sucker (C. discobolus) and roundtail chub (Gila robusta), have experienced the establishment of numerous non‐native fish species. In this study, we examine the impacts of the trophic ecology of non‐native fishes on the ‘three species’ in the San Rafael River, Utah, USA. We employ a suite of abundance comparisons, stable isotope techniques and size‐at‐age back‐calculation analyses to compare food web structure and growth rates of the ‘three species’ in study areas with and without established populations of non‐native species. We found that the ‘three species’ are more abundant in areas with few non‐native fishes present, regardless of habitat complexity. Stable isotope analyses indicate non‐native fishes lengthen the food chain by 0.5 trophic positions. Further, the trophic niche spaces of the native fishes shift and are narrower in the presence of non‐native fishes, as several non‐native species’ trophic niche spaces overlap almost entirely with each of the ‘three species’ (bluehead sucker and flannelmouth sucker 100%, roundtail chub 98.5%) indicating strong potential for competition. However, the ‘three species’ demonstrated no evidence of reduced growth in the presence of these non‐native fishes. Collectively, these results suggest that while non‐native fishes alter the food web structure presenting novel sources of predation and competition, mechanisms other than competition are controlling the size‐structure of ‘three species’ populations in the San Rafael River.

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.

Bioenergetics and Population Dynamics of Flannelmouth Sucker and Bluehead Sucker in Grand Canyon as Evidenced by Tag Recapture Observations

AbstractFlannelmouth suckers Catostomus latipinnus and bluehead suckers C. discolobus in the Grand Canyon of the Colorado River are among the few native species to persist after river conditions changed with the completion of Glen Canyon Dam in 1963. To evaluate the effectiveness of adaptive management manipulations to the system for recovering native species, it is necessary to estimate basic demographic and population dynamic parameters for the species of interest, such as growth, mortality, and recruitment. With this in mind, we present a two‐stage analysis in which we first estimated growth and individual ages using a field‐based bioenergetics model and then input the age estimates into age‐structured mark–recapture (ASMR) models to estimate mortality and recruitment. The analysis was based on 18,500 flannelmouth suckers and 13,975 bluehead suckers that had been tagged with passive integrated transponder tags in the main‐stem Colorado River in Grand Canyon and its tributaries since 1989. The bioenergetics estimates of growth suggest that the growth of flannelmouth suckers is faster and that of bluehead suckers slower than in the tributaries reported in other studies. The results from the bioenergetics model provide necessary parameters for input into future ecosystem models. The ASMR models that include the effects of age‐specific gear vulnerability indicate that annual natural mortality rates are about 0.2 for flannelmouth suckers and 0.4 for bluehead suckers, which is in agreement with independent estimates from growth parameters and longevity. The estimates of age‐1 sucker recruitment and adult abundance correspond well with independent electrofishing catch rate data. The estimated recruitment and abundance estimates provide insights into the efficacy of adaptive management actions targeted to benefit native fishes over the past two decades.

Identification and Implementation of Native Fish Conservation Areas in the Upper Colorado River Basin

AbstractFreshwater fishes continue to decline at a rapid rate despite substantial conservation efforts. Native fish conservation areas (NFCAs) are a management approach emphasizing persistent native fish communities and healthy watersheds while simultaneously allowing for compatible human uses. We identified potential NFCAs in the Upper Colorado River Basin in Wyoming—focusing on Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus), flannelmouth sucker (Catostomus latipinnis), bluehead sucker (Catostomus discobolus), and roundtail chub (Gila robusta)—through a process that combined known and modeled species distributions, spatial prioritization analysis, and stakeholder discussions. The network of potential NFCAs is intended to serve as a funding framework for a National Fish and Wildlife Foundation (NFWF) Keystone Initiative focused on Colorado River Basin native fishes. We discuss current opportunities for and impediments to implementing the potential NFCAs we identified for the NFWF Initiative over the long term. NFCAs represent a promising approach to fisheries management that complements existing approaches by focusing on persistent native fish communities.

Land Use Associations with Distributions of Declining Native Fishes in the Upper Colorado River Basin

AbstractThe upper Colorado River basin contains one of the most imperiled fish faunas in North America. Anthropogenic land use and nonnative species impacts are considered among the top reasons for imperilment. We determined the association of anthropogenic land use intensity (road density, percentage of converted land, and oil and gas well density), relative abundance of nonnative white suckers Catostomus commersonii and their hybrids, and natural landscape features with the occurrences of three native fishes in the Colorado River basin, Wyoming, that have declined throughout their ranges: flannelmouth sucker C. latipinnis, bluehead sucker C. discobolus, and roundtail chub Gila robusta. We found that flannelmouth suckers occurred more frequently in large, low‐gradient stream reaches, but their occurrence was not associated with land use intensity or the relative abundance of white suckers and hybrid suckers. In contrast, bluehead sucker occurrence decreased with increasing intensity of each land use type within a 0.5‐km stream buffer, which suggests that localized land use disturbances have negatively affected the species’ distribution. Roundtail chub occurred more frequently in low‐gradient stream segments with more riparian vegetation, but associations with land uses were more complex. Roundtail chub were negatively associated with road density in a 0.5‐km buffer, but in contrast to our expectations they were positively associated with road density in the contributing watershed and with local oil and gas well density. We think that rocky substrates and pools—habitats preferred by roundtail chub and sometimes associated with oil and gas infrastructure—have concentrated the remaining individuals within their currently reduced distribution. The associations we identified highlight the potential role of land use in distributional declines and can help managers to determine whether proposed land use changes may affect existing populations. Spatial predictions of occurrence have already been used in regional fish conservation planning efforts in Wyoming.

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.

Seasonal Movements of Native and Introduced Catostomids in the Big Sandy River, Wyoming

During 2006–2007, we studied movements of native bluehead suckers (Catostomus discobolus) and flannelmouth suckers (C. latipinnis), and non-native white suckers (C. commersonii) and longnose suckers (C. catostomus) in the Big Sandy River, Wyoming. Radiotransmitters were surgically implanted into 20–22 fish of each species in September and October 2006. Movements of all four species in autumn and winter were short with most fish remaining ≤2 km from locations where they were captured initially. Bluehead suckers and flannelmouth suckers began movements downstream in mid-to-late April and returned upstream to locations ≤2 km from their original locations by early summer. White suckers did not make substantial movements during spring, whereas longnose suckers made movements upstream during mid-June and returned downstream by early July. During their estimated spawning periods, longnose suckers used upstream portions, bluehead suckers and white suckers used middle portions, and flannelmouth suckers used downstream portions of the study area.

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.

Morphometric and Meristic Differences among Bluehead Suckers, Flannelmouth Suckers, White Suckers, and Their Hybrids: Tools for the Management of Native Species in the Upper Colorado River Basin

AbstractHybridization with nonnative fishes is a major factor influencing the status of native catostomids in the Colorado River basin. In Wyoming, hybridization with nonnative white suckers Catostomus commersonii is a particular concern in the conservation of native bluehead suckers C. discobolus and flannelmouth suckers C. latipinnis. The purpose of this study was to describe the meristic and morphometric characteristics of bluehead suckers, flannelmouth suckers, white suckers, and their hybrids from Muddy Creek, Wyoming, for which genotypic data were available to verify the classification of individual fish as pure species or hybrids. We also sought to develop discriminant function models that can be used in the field. Bluehead suckers and flannelmouth suckers had more lateral line scales, shorter and narrower heads, and narrower caudal peduncles than white suckers. Bluehead suckers and bluehead sucker × white sucker hybrids had a cartilaginous biting ridge in their mouth. Important characteristics for discriminating among these taxa included the number of postdorsal lateral line scales and the exterior width of the mouth. The discriminant function correctly classified 100% of the bluehead suckers and bluehead sucker × white sucker hybrids. Flannelmouth suckers, white suckers, and flannelmouth sucker × white sucker hybrids lacked a cartilaginous biting ridge. The number of postdorsal scales, caudal peduncle depth, and ratio of mouth length to the interior width of the mouth discriminated among taxa without a ridge. The discriminant function correctly classified 100% of the flannelmouth suckers, 92% of the white suckers, and 91% of the flannelmouth sucker × white sucker hybrids. None of the white suckers or flannelmouth sucker × white sucker hybrids were misclassified as flannelmouth suckers. Our results suggest that native bluehead suckers and flannelmouth suckers, nonnative white suckers, and hybrids of these species can be accurately identified by a few, easily measured meristic and morphometric characteristics.

Age and Growth of Bluehead Suckers and Flannelmouth Suckers in Headwater Tributaries, Wyoming

ABSTRACT. Bluehead sucker (Catostomus discobolus) and flannelmouth sucker (Catostomus latipinnis) populations are declining throughout these species' native ranges in the Upper Colorado River Basin. In order to conserve these populations, an understanding of population dynamics is needed. Using age estimates from pectoral fin rays, we describe age and growth of these 2 species in 3 Wyoming stream systems: Muddy Creek, the Little Sandy River, and the Big Sandy River. Within all 3 stream systems, flannelmouth suckers were longer-lived than bluehead suckers, with maximum estimated ages of 16 years in Muddy Creek, 18 years in Little Sandy Creek, and 26 years in the Big Sandy River. Bluehead suckers had maximum estimated ages of 8 years in Muddy Creek, 10 years in Little Sandy Creek, and 18 years in the Big Sandy River. These maximum estimated ages were substantially greater than in other systems where scales have been used to estimate ages. Mean lengths at estimated ages were greater for flannelmouth suckers ...

Influences of Fragmentation on Three Species of Native Warmwater Fishes in a Colorado River Basin Headwater Stream System, Wyoming

AbstractWe 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 of the three target fishes were common. Fish of all three species moved frequently downstream over both structures, displayed some upstream movements over the irrigation diversion dam, and did not move upstream over the fish barrier. Spawning migrations by some fish into an intermittent tributary, which was not separated from Muddy Creek by a barrier, were observed for all three species. Both the irrigation diversion dam and the fish barrier contributed to fragmentation of the native fish populations, and considerable differences in population features were observed among segments. The instream structures may eventually cause extirpation of some native species in one or more of the segments created by the structures.

An introduced and a native vertebrate hybridize to form a genetic bridge to a second native species

The genetic impacts of hybridization between native and introduced species are of considerable conservation concern, while the possibility of reticulate evolution affects our basic understanding of how species arise and shapes how we use genetic data to understand evolutionary diversification. By using mitochondrial NADH dehydrogenase subunit 2 (ND2) sequences and 467 amplified fragment-length polymorphism nuclear DNA markers, we show that the introduced white sucker (Catostomus commersoni) has hybridized with two species native to the Colorado River Basin--the flannelmouth sucker (Catostomus latipinnis) and the bluehead sucker (Catostomus discobolus). Hybrids between the flannelmouth sucker and white sucker have facilitated introgression between the two native species, previously isolated by reproductive barriers, such that individuals exist with contributions from all three genomes. Most hybrids had the mitochondrial haplotype of the introduced white sucker, emphasizing its pivotal role in this three-way hybridization. Our findings highlight how introduced species can threaten the genetic integrity of not only one species but also multiple previously reproductively isolated species. Furthermore, this complex three-way reticulate (as opposed to strictly bifurcating) evolution suggests that seeking examples in other vertebrate systems might be productive. Although the present study involved an introduced species, similar patterns of hybridization could result from natural processes, including stream capture or geological formations (e.g., the Bering land bridge).

Habitat Features Affect Bluehead Sucker, Flannelmouth Sucker, and Roundtail Chub across a Headwater Tributary System in the Colorado River Basin

ABSTRACT We assessed the distributions of three species of conservation concern, bluehead sucker (Catostomus discobolus), flannelmouth sucker (Catostomus latipinnis), and roundtail chub (Gila robusta), relative to habitat features across a headwater tributary system of the Colorado River basin in Wyoming. We studied the upper Muddy Creek watershed, Carbon County, portions of which experience intermittent flows during late summer and early fall. Fish and habitat were sampled from 57 randomly-selected, 200-m reaches and 416 habitat units (i.e., pools, glides, or runs) during the summer and fall of 2003 and 2004. Among reaches, the occurrences of adults and juveniles of all three species were positively related to mean wetted width and the surface area of pool habitat, and the occurrences of adult bluehead sucker and roundtail chub were also positively related to the abundance of rock substrate. Only juvenile bluehead sucker appeared to be negatively influenced by the proportion of a reach that was dry at the time of sampling. Within individual pools, glides, and runs, the occurrences of adults and juveniles of all three species were positively related to surface area and maximum depth, and occurrences of bluehead sucker and flannelmouth sucker juveniles were more probable in pools than in glides or runs.

Precision of Hard Structures Used to Estimate Age of Riverine Catostomids and Cyprinids in the Upper Colorado River Basin

AbstractUnderstanding 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 sucker × bluehead sucker hybrids, and white sucker × flannelmouth sucker hybrids in a small headwater stream of the upper Colorado River basin (UCRB) in Wyoming. We evaluated between‐reader precision (i.e., between two readers) and agreement of otolith age estimates with estimates from scales, fin rays, cleithra, and opercular bones. Exact agreement between readers was highest for otoliths (66–96% among species) and fin rays (61–92%) and lowest for opercles (25–69%), cleithra (21–41%), and scales (15–48%). Age estimates from fin rays were almost exactly the same as those from otoliths for all species except creek chub, for which fin ray estimates were consistently lower than otolith estimates. Age estimates from scales were generally 1–4 years lower than those from otoliths for most species, and most discrepancies occurred when otolith ages were greater than 5 years. We recommend that fin rays be used to estimate age of native catostomids and roundtail chub in the UCRB because fin rays provide accurate estimates of otolith age and can be obtained without sacrificing fish. We further recommend that otoliths be used to estimate age of creek chub in the UCRB because accuracy of fin rays was poor and because sacrificing this nonnative species may benefit native fishes of the UCRB.

Infection by a black spot-causing species of Uvulifer and associated opercular alterations in fishes from a high-desert stream in Wyoming

Black spot is a common disease syndrome of freshwater fishes. This study provides information on the rank of density of the black spot agent and opercular bone alterations associated with at least one digenean, Uvulifer sp., infecting native and non-native catostomids and cyprinids of the Upper Colorado River Basin. We evaluated the density rank of pigmented metacercariae and associated alterations in the operculum of the bluehead sucker Catostomus discobolus, flannelmouth sucker C. latipinnis, white sucker C. commersoni, catostomid hybrids, roundtail chub Gila robusta, and creek chub Semotilus atromaculatus, sampled from Muddy Creek, Wyoming, USA in 2003 or 2004. All fish species contained individuals that exhibited gross signs of the black spot agent. Bluehead and flannelmouth suckers had 100% prevalence of infection. Although the other suckers and chubs contained encysted metacercariae in at least one individual, the presence of pigmented metacercariae was not apparent (i.e. based on gross observations) in many individuals. Catostomids had higher densities of metacercariae than cyprinids, as shown by frequency distributions of density ranks. Opercular holes (i.e. holes that completely penetrated the opercle and were in direct association with the pigment associated metacercariae) and pockets (depressions on the external surface of the opercle associated with metacercariae) were abundant among catostomids but rare among cyprinids.

Spatial Patterns of Fish Assemblage Structure in a Tributary System of the Upper Colorado River Basin

ABSTRACT This study was conducted to describe the distributions of both native and nonnative fishes and to identify spatial patterns in fish assemblage structure of Muddy Creek in the upper Colorado River basin of Wyoming using data collected from 77 reaches during 1999–2004. Fish assemblages in high-elevation reaches were characterized by brook trout (Salvelinus fontinalis) and represented a coldwater faunal zone. Reaches at lower elevations were characterized by warmwater fish species. The upper segment of the warmwater faunal zone contained four native (i.e., bluehead sucker [Catostornus discobolus], flannelmouth sucker [C. latipinnis], speckled dace [Rhinichthys osculus], roundtail chub [Gila robusta]) and two nonnative (i.e., white sucker [C. commersoni] and creek chub [Semotilus atromaculatus]) species. The lower segment of the warmwater faunal zone included species present in upstream segments and three additional nonnative species (i.e., common carp [Cyprinus carpio], redside shiner [Richardsonius baleatus], and fathead minnow [Pimephales promelas]). Differences in fish assemblage structure between coldwater and warmwater faunal zones were likely due to physiological constraints of species adapted for either coldwater or warmwater habitats. Changes in fish assemblages over the warmwater faunal zone are due to introduction and naturalization of nonnative fishes and anthropogenic barriers preventing upstream movements and colonization by some of these species.

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.

SUMMER FOOD HABITS AND TROPHIC OVERLAP OF ROUNDTAIL CHUB AND CREEK CHUB IN MUDDY CREEK, WYOMING

Abstract Native fishes of the Upper Colorado River Basin have experienced substantial declines in abundance and distribution, and are extirpated from most of Wyoming. Muddy Creek, in south-central Wyoming (Little Snake River watershed), contains sympatric populations of native roundtail chub (Gila robusta), bluehead sucker, (Catostomus discobolus), and flannelmouth sucker (C. latipinnis), and represents an area of high conservation concern because it is the only area known to have sympatric populations of all 3 species in Wyoming. However, introduced creek chub (Semotilus atromaculatus) are abundant and might have a negative influence on native fishes. We assessed summer food habits of roundtail chub and creek chub to provide information on the ecology of each species and obtain insight on potential trophic overlap. Roundtail chub and creek chub seemed to be opportunistic generalists that consumed a diverse array of food items. Stomach contents of both species were dominated by plant material, aquatic and...