Gila Robusta Research Articles

Molecular Genetics Informs Spatial Segregation of Two Desert Stream Gila Species

AbstractHeadwater Chub Gila nigra and Roundtail Chub G. robusta are two distinct but morphologically similar cyprinid species that historically were parapatric in Fossil Creek (Gila River basin) in central Arizona. The creek was chemically treated in 2005 to eradicate nonnative fishes, and chubs salvaged before the treatment were repatriated afterward. Annual samples from multiple sites along a transect throughout the treated reach were characterized for mtDNA and microsatellites from 2008 to 2014. Genetic variation was compared within and among Fossil Creek samples and with reference material for Headwater Chub from Fossil Springs at the headwaters of the creek and for Roundtail Chub from the Verde River and West Clear Creek. Measures of mtDNA and microsatellite diversity identified significant differences among Headwater Chub from Fossil Springs, Roundtail Chub from the Verde River, and samples above and below Irving Falls, a natural fish barrier within the treatment reach. The frequency of Headwater Chub mtDNA was low at the most downstream sampling sites, progressively increasing upstream. There was also temporal variation, with Headwater Chub mtDNA generally becoming rarer in later samples. F‐statistic analysis of microsatellite data and Bayesian clustering of microsatellite genotypes with STRUCTURE were generally consistent and identified three groups: Headwater Chub and two forms of Roundtail Chub. Using the species assignments provided by STRUCTURE and mitotypes, we found 153 “pure” Headwater Chub and only a single pure Roundtail Chub above Irving Falls and 27 pure Headwater Chub and 398 pure Roundtail Chub below the falls. Tests of cytonuclear disequilibrium indicated nonrandom mating (with the rare species more likely to mate than the more common one) and/or selection against hybrids. These data support the recognition of the Headwater Chub as a distinct full species and demonstrate that conservation actions within the genus Gila should typically be carried out at the population level.Received April 8, 2016; accepted August 16, 2016 Published online December 2, 2016

Why does Gila elegans have a bony tail? A study of swimming morphology convergence

Caudal-fin-based swimming is the primary form of locomotion in most fishes. As a result, many species have developed specializations to enhance performance during steady swimming. Specializations that enable high swimming speeds to be maintained for long periods of time include: a streamlined body, high-aspect-ratio (winglike) caudal fin, a shallow caudal peduncle, and high proportions of slow-twitch (“red”) axial muscle. We described the locomotor specializations of a fish species native to the Colorado River and compared those specializations to other fish species from this habitat, as well as to a high-performance marine swimmer. The focal species for this study was the bonytail (Gila elegans), which has a distinct morphology when compared with closely related species from the Southwestern United States. Comparative species used in this study were the roundtail chub (Gila robusta), a closely related species from low-flow habitats; the common carp (Cyprinus carpio), an invasive cyprinid also found in low-flow habitats; and the chub mackerel (Scomber japonicus), a model high-performance swimmer from the marine environment. The bonytail had a shallow caudal peduncle and a high-aspect-ratio tail that were similar to those of the chub mackerel. The bonytail also had a more streamlined body than the roundtail chub and the common carp, although not as streamlined as the chub mackerel. The chub mackerel had a significantly higher proportion of red muscle than the other three species, which did not differ from one another. Taken together, the streamlined body, narrow caudal peduncle, and high-aspect-ratio tail of the bonytail suggest that this species has responded to the selection pressures of the historically fast-flowing Colorado River, where flooding events and base flows may have required native species to produce and sustain very high swimming speeds to prevent being washed downstream.

Effects of Water Temperature and Fish Size on Predation Vulnerability of Juvenile Humpback Chub to Rainbow Trout and Brown Trout

AbstractPredation on juvenile native fish by introduced Rainbow Trout and Brown Trout is considered a significant threat to the persistence of endangered Humpback Chub Gila cypha in the Colorado River in the Grand Canyon. Diet studies of Rainbow Trout and Brown Trout in Glen and Grand canyons indicate that these species do eat native fish, but impacts are difficult to assess because predation vulnerability is highly variable, depending on prey size, predator size, and the water temperatures under which the predation interactions take place. We conducted laboratory experiments to evaluate how short‐term predation vulnerability of juvenile native fish changes in response to fish size and water temperature using captivity‐reared Humpback Chub, Bonytail, and Roundtail Chub. Juvenile chub 45–90 mm total length (TL) were exposed to adult Rainbow and Brown trouts at 10, 15, and 20°C to measure predation vulnerability as a function of water temperature and fish size. A 1°C increase in water temperature decreased short‐term predation vulnerability of Humpback Chub to Rainbow Trout by about 5%, although the relationship is not linear. Brown Trout were highly piscivorous in the laboratory at any size > 220 mm TL and at all water temperatures we tested. Understanding the effects of predation by trout on endangered Humpback Chub is critical in evaluating management options aimed at preserving native fishes in Grand Canyon National Park.

Population Structure in the Roundtail Chub (Gila robusta Complex) of the Gila River Basin as Determined by Microsatellites: Evolutionary and Conservation Implications

Ten microsatellite loci were characterized for 34 locations from roundtail chub (Gila robusta complex) to better resolve patterns of genetic variation among local populations in the lower Colorado River basin. This group has had a complex taxonomic history and previous molecular analyses failed to identify species diagnostic molecular markers. Our results supported previous molecular studies based on allozymes and DNA sequences, which found that most genetic variance was explained by differences among local populations. Samples from most localities were so divergent species-level diagnostic markers were not found. Some geographic samples were discordant with current taxonomy due to admixture or misidentification; therefore, additional morphological studies are necessary. Differences in spatial genetic structure were consistent with differences in connectivity of stream habitats, with the typically mainstem species, G. robusta, exhibiting greater genetic connectedness within the Gila River drainage. No species exhibited strong isolation by distance over the entire stream network, but the two species typically found in headwaters, G. nigra and G. intermedia, exhibited greater than expected genetic similarity between geographically proximate populations, and usually clustered with individuals from the same geographic location and/or sub-basin. These results highlight the significance of microevolutionary processes and importance of maintaining local populations to maximize evolutionary potential for this complex. Augmentation stocking as a conservation management strategy should only occur under extreme circumstances, and potential source populations should be geographically proximate stocks of the same species, especially for the headwater forms.

Integrating Nonnative Species in Niche Models to Prioritize Native Fish Restoration Activity Locations along a Desert River Corridor

AbstractThe efficient allocation of restoration resources is critical for the effective conservation of species. Here, we developed an ecological niche model to predict the response of three imperiled desert fishes to potential restoration actions along the longitudinal gradient of a desert river. The San Rafael River, Utah, is home to a complex of three endemic fishes (Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta; referred to as the “three species”). Like many Colorado River basin tributaries, the river is overallocated for human use, has experienced extensive physical degradation, and is now home to several nonnative fish species. To determine the factors most limiting to the three species, we first fit random forest models to fish CPUE and habitat data. We next combined these models with a longitudinal habitat survey and modeled nonnative species abundance to predict the continuous distribution of the three species in the lower San Rafael River, under current conditions and following simulated restoration. Nonnative fishes were important negative predictors of Flannelmouth Sucker and Bluehead Sucker relative abundance, and broadscale habitat variables were important positive predictors for all of the three species. Each of the three species was predicted to experience a significant increase in abundance following simulated eradication of nonnative fishes. Responses to simulated reach‐specific habitat restoration were dependent on the reach restored, demonstrating that the choice of restoration location is critical. Nonnative species removal and restoring degraded reaches near already suitable habitat were predicted to be the most beneficial to the three species. Ecological niche models developed at the river scale, and incorporating both physical and biotic predictor variables, can provide spatially explicit information that appropriately parallels the spatial distribution of the needs of endemic fishes and can facilitate effective management and conservation decisions.

An occupancy-based quantification of the highly imperiled status of desert fishes of the southwestern United States.

Desert fishes are some of the most imperiled vertebrates worldwide due to their low economic worth and because they compete with humans for water. An ecological complex of fishes, 2 suckers (Catostomus latipinnis, Catostomus discobolus) and a chub (Gila robusta) (collectively managed as the so-called three species) are endemic to the U.S. Colorado River Basin, are affected by multiple stressors, and have allegedly declined dramatically. We built a series of occupancy models to determine relationships between trends in occupancy, local extinction, and local colonization rates, identify potential limiting factors, and evaluate the suitability of managing the 3 species collectively. For a historical period (1889-2011), top performing models (AICc) included a positive time trend in local extinction probability and a negative trend in local colonization probability. As flood frequency decreased post-development local extinction probability increased. By the end of the time series, 47% (95% CI 34-61) and 15% (95% CI 6-33) of sites remained occupied by the suckers and the chub, respectively, and models with the 2 species of sucker as one group and the chub as the other performed best. For a contemporary period (2001-2011), top performing (based on AICc ) models included peak annual discharge. As peak discharge increased, local extinction probability decreased and local colonization probability increased. For the contemporary period, results of models that split all 3 species into separate groups were similar to results of models that combined the 2 suckers but not the chub. Collectively, these results confirmed that declines in these fishes were strongly associated with water development and that relative to their historic distribution all 3 species have declined dramatically. Further, the chub was distinct in that it declined the most dramatically and therefore may need to be managed separately. Our modeling approach may be useful in other situations in which targeted data are sparse and conservation status and best management approach for multiple species are uncertain.

Comparative Swimming Performance of Five Catostomus Species and Roundtail Chub

Abstract.—Decreased habitat connectivity and competition with nonnative species have led to declines of many freshwater fishes. An understanding of swimming performance can aid in the conservation of these fishes; however, acquiring sufficient numbers of rare and threatened species to perform swimming studies can be logistically challenging and ecologically costly. In order to determine whether swimming data for common sucker species may be substituted for that of similar but rare sucker species, we compared the swimming abilities of two rare western catostomids, Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker C. latipinnis, as well as one catostomid with a less well understood status, Mountain Sucker C. platyrhynchus, with those of the common White Sucker C. commersonii and Longnose Sucker C. catostomus. We also examined Roundtail Chub Gila robusta because they are often included in conservation efforts involving Bluehead Sucker and Flannelmouth Sucker. The critical swimming velocities (Ucrit), standardized by body length, of Bluehead Sucker and Longnose Sucker differed significantly from those of White Sucker. However, there was no significant difference between the Ucrit of Mountain Sucker, Flannelmouth Sucker, and White Sucker. During constant acceleration trials, Bluehead Sucker exhibited the greatest swimming ability, reaching a mean maximum velocity of 4.56 ± 1.28 body lengths per second (BL/s; mean ± SD), followed by Mountain Sucker (3.56 ± 0.57 BL/s), White Sucker (3.28 ± 0.90 BL/s), Longnose Sucker (2.97 ± 0.31 BL/s), and Flannelmouth Sucker (2.22 ± 0.42 BL/s). Additionally, key behavioral differences in the swimming behaviors of the fishes studied were observed. We conclude that swimming performance data for common White Sucker should not be used in place of data for rarer species. Comprehensive swimming studies should be conducted on individual sucker species before implementing conservation strategies involving fish passageways or barriers.Received November 6, 2013; accepted February 28, 2014

Behaviors of Southwestern Native Fishes in Response to Introduced Catfish Predators

Abstract Native fishes reared in hatcheries typically suffer high predation mortality when stocked into natural environments. We evaluated the behavior of juvenile bonytail Gila elegans, roundtail chub Gila robusta, razorback sucker Xyrauchen texanus, and Sonora sucker Catostomus insignis in response to introduced channel catfish Ictalurus punctatus and flathead catfish Pylodictis olivaris. Our laboratory tests indicate these species did not inherently recognize catfish as a threat, but they can quickly (within 12 h) change their behavior in response to a novel predator paired with the sight and scent of a dead conspecific. Chubs appear to avoid predation by swimming away from the threat, whereas suckers reduced movement. Effects of antipredator conditioning on survival of fish reared in hatcheries is unknown; however, our results suggest some native fish can be conditioned to recognize introduced predators, which could increase poststocking survival.

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.

Salinity of the Little Colorado River in Grand Canyon Confers Anti-Parasitic Properties on a Native Fish

ABSTRACT. Water in the Little Colorado River within Grand Canyon is naturally high in salt (NaCl), which is known to prohibit development of external fish parasites such as Ich (Ichthyophthirius multifiliis). The naturally high salinity (>0.3%) of the Little Colorado River at baseflow may be one factor allowing survival and persistence of larval and juvenile humpback chub (Gila cypha) and other native fishes in Grand Canyon. We compared salinity readings from the Little Colorado River to those reported in the literature as being effective at removing protozoan parasites from fish. In laboratory tests, 10 juvenile roundtail chub (Gila robusta; 61–90 mm TL) were randomly placed into each of 12, 37-L aquaria filled with freshwater, water obtained from the Little Colorado River (0.3% salinity), or freshwater with table salt added until the salinity reached 0.3%. Roundtail chub was used as a surrogate for humpback chub in this study because the species is not listed as endangered but is morphologically and eco...

Effects of Capture by Trammel Net on Colorado River Native Fishes

Abstract Trammel nets are commonly used to sample rare fishes; however, little research has assessed delayed mortality associated with this capture technique. We conducted laboratory experiments to evaluate the effects of capture by trammel net on bonytail Gila elegans, razorback sucker Xyrauchen texanus, and roundtail chub Gila robusta, at 15, 20, and 25°C. Fish (139–288 mm total length) were entangled in a trammel net for 2 h or captured by seine net and then monitored for mortality for at least 14 d. Blood samples were collected immediately after capture, and plasma cortisol levels were quantified as an index of capture-related stress. The cortisol response varied by species, but mean cortisol levels were higher for fish captured by trammel netting (295.9 ng/mL) relative to fish captured by seine netting (215.8 ng/mL). Only one fish (of 550) died during capture and handling, but 42% of the trammel-netted fish and 11% of the seine-netted fish died within 14 d after capture. In general, mortality after capture by trammel net increased with increased water temperature and at 25°C was 88% for bonytail, 94% for razorback sucker, and 25% for roundtail chub. Delayed mortality of wild-caught fish captured by trammel net has the potential to be high, at least under some circumstances. We suggest that sampling frequency, timing of sampling (relative to reproductive cycles), and water temperature all be considered carefully when using trammel nets to sample diminished populations of imperiled native fishes.

Differential Interactions of Two Introduced Piscivorous Salmonids with a Native Cyprinid in Lentic Systems: Implications for Conservation of Roundtail Chub

AbstractThe effects of multiple nonnative piscivore species on native prey species in lentic systems are poorly understood. We studied the relative predation risks posed by two piscivorous salmonids (brown trout Salmo trutta and lake trout Salvelinus namaycush) to endemic roundtail chub Gila robusta in two lakes within the upper Colorado River basin. Gill nets were set in various habitat types to study habitat use by the three species before and after the onset of summer stratification. Roundtail chub and brown trout were mainly associated with shallow‐water habitats, and this association did not change with thermal period. By contrast, lake trout habitat use changed with thermal period as fish moved from shallow areas in the spring to deepwater habitat after stratification. These habitat use patterns indicate that roundtail chub are more susceptible to predation by brown trout than by lake trout because both roundtail chub and brown trout occupy the littoral zone for a prolonged period. Diet data indicated that brown trout consumed littoral fish species (i.e., cyprinids), whereas lake trout primarily consumed opossum shrimp Mysis spp. and dipterans (true flies). Brown trout consumed proportionally more fish than did lake trout, began feeding on fish at smaller total lengths, and increased fish consumption during the period of thermal stratification. An important consideration for efforts to conserve lentic roundtail chub populations is the prevention of future introductions of littoral predators.

Do lower feeding rates result in reduced growth of a cyprinid fish infected with the Asian tapeworm?

Ecology of Freshwater FishVolume 21, Issue 2 p. 172-175 Letter Do lower feeding rates result in reduced growth of a cyprinid fish infected with the Asian tapeworm? J. Robert Britton, J. Robert Britton Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorJosephine Pegg, Josephine Pegg Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorDavid Baker, David Baker Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorChris F. Williams, Chris F. Williams Environment Agency, Bromholme Lane, Brampton, Cambridgeshire, PE28 4NE, UKSearch for more papers by this author J. Robert Britton, J. Robert Britton Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorJosephine Pegg, Josephine Pegg Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorDavid Baker, David Baker Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UKSearch for more papers by this authorChris F. Williams, Chris F. Williams Environment Agency, Bromholme Lane, Brampton, Cambridgeshire, PE28 4NE, UKSearch for more papers by this author First published: 08 February 2012 https://doi.org/10.1111/j.1600-0633.2012.00551.xCitations: 6 Dr. Robert Britton, Centre for Conservation Ecology & Environmental Change, Bournemouth University, Poole, BH12 5BB, UK. E-mail: rbritton@bournemouth.ac.uk Read the full textAboutRelatedInformationPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessClose modalShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume21, Issue2April 2012Pages 172-175 RelatedInformation RecommendedRelationship between Length of Roundtail Chub and Infection Intensity of Asian Fish Tapeworm Bothriocephalus acheilognathiMark J. Brouder, Journal of Aquatic Animal HealthAsian Fish Tapeworm Bothriocephalus acheilognathi in the Desert Southwestern United StatesThomas P. Archdeacon, Alison Iles, Jason S. Kline, Scott A. Bonar, Journal of Aquatic Animal HealthNovel Praziquantel Treatment Regime for Controlling Asian Tapeworm Infections in Pond‐Reared FishAlison C. Iles, Thomas P. Archdeacon, Scott A. Bonar, North American Journal of AquacultureEffects of Praziquantel on Eggs of the Asian Tapeworm Bothriocephalus acheilognathiS. Jason Kline, Thomas P. Archdeacon, Scott A. Bonar, North American Journal of AquacultureOptimization of feeding quantity and frequency to rear the cyprinid fish Garra rufa (Heckel, 1843)Mafalda M. R. S. Catarino, Mónica R. S. Gomes, Susana M. F. Ferreira, Sílvia C. Gonçalves, Aquaculture Research

Prey Capture Behavior of Native vs. Nonnative Fishes: A Case Study From the Colorado River Drainage Basin (USA)

The Colorado River drainage basin is home to a diverse but imperiled fish fauna; one putative challenge facing natives is competition with nonnatives. We examined fishes from Colorado River tributaries to address the following questions: Do natives and nonnatives from the same trophic guild consume the same prey items? Will a given species alter its behavior when presented with different prey types? Do different species procure the same prey types via similar feeding behaviors? Roundtail chub (Gila robusta) and smallmouth bass (Micropterus dolomieu), midwater predators, and Sonora sucker (Catostomus insignis) and common carp (Cyprinus carpio), benthic omnivores, were offered six ecologically relevant prey types in more than 600 laboratory trials. Native species consumed a broader array of prey than nonnatives, and species from a given trophic guild demonstrated functional convergence in key aspects of feeding behavior. For example, roundtail chub and smallmouth bass consume prey attached to the substrate by biting, then ripping the prey from its point of attachment; in contrast, Sonora sucker remove attached prey via scraping. When presented with different prey types, common carp, roundtail chub, and smallmouth bass altered their prey capture behavior by modifying strike distance, gape, and angle of attack. Gape varied among the species examined here, with smallmouth bass demonstrating the largest functional and anatomical gape at a given body size. Because fish predators are gape-limited, smallmouth bass will be able to consume a variety of large prey items in the wild, including large, invasive crayfish and young roundtail chub-their presumptive trophic competitors.

Ecology of Unique Lentic Populations of Roundtail Chub,Gila robusta

ABSTRACT. Although roundtail chub (Gila robusta) is generally considered a riverine species, 6 natural lakes in the upper Green River basin, Wyoming, have resident populations of this fish. In 2 of the lakes, Halfmoon and Little Halfmoon, we investigated the ecology of resident roundtail chub, including their habitat use, diet, weight—length relationships, growth, and reproduction. Lentic roundtail chub used littoral and mid-depth benthic habitats most often, with the highest catch rates in littoral habitats. Roundtail chub were rarely caught in pelagic or deep benthic habitats. Opportunistic foraging was observed in both lakes, with roundtail chub consuming terrestrial and aquatic insects, vegetation, and fish. Roundtail chub from both lakes had weight—length relationships similar to those reported for lotic populations but slower annual growth rates. Fish in spawning condition were captured from mid-June to late July when water temperatures ranged from 8.7 to 18.3 °C and snowmelt runoff was at its maxim...

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.

Complex influences of low‐head dams and artificial wetlands on fishes in a Colorado River tributary system

Abstract Low‐head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low‐head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non‐native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacepède). Downstream, fish assemblages were dominated by non‐native species. Upstream spawning migrations by non‐native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non‐native fishes and a sink habitat for native fishes. Two non‐native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non‐native fishes.

Survival, Condition, Habitat Use, and Predation on Stocked Bonytails (Gila elegans) in the Green River, Colorado and Utah

The endangered bonytail Gila elegans, a large-bodied, main-stem cyprinid endemic to the Colorado River Basin of the American Southwest, was once widespread and abundant in warm-water-stream reaches. Negative effects of altered flow and temperature regimes downstream of dams, other habitat changes, and establishment of nonnative fishes have reduced populations of native fish throughout the basin, and wild bonytails may be extirpated. Hatchery reared bonytails are stocked in formerly occupied habitat to rebuild depleted populations, but their ecology is poorly understood. In 2002–2007, sampling in the middle Green River from upstream and downstream of stocking locations in Dinosaur National Monument documented survival of bonytails for ≤4 months, but apparently none survived longer. Many fish at large ≤4 months had Lernea or fungal infections, weighed an average of 20% less than fish when released, and had relatively low rates of growth. Post-stocking rates of dispersal downstream (ca. 1 river km/day) were considerable, and potentially, biologically significant. Bonytails occupied pools, eddies, runs, backwaters, and riffles, and co-occurred in eddies with the roundtail chub Gila robusta and humpback chub Gila cypha in Whirlpool Canyon. We also documented two instances of predation by smallmouth bass Micropterus dolomieu on bonytails ≤225 mm in total length. Reduced predation by large-bodied, nonnative, piscivores and increased resistance to disease and other stressors that reduce body condition may increase survival of stocked bonytails in this portion of the Green River. Alternative stocking strategies, including use of alluvial and floodplain areas, and effects of size on survival, are being evaluated.

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.