Bluehead Sucker Research Articles

Translocation in a fragmented river provides demographic benefits for imperiled fishes

AbstractFragmentation isolates individuals and restricts access to valuable habitat with severe consequences for populations, such as reduced gene flow, disruption of recolonization dynamics, reduced resiliency to disturbance, and changes in aquatic community structure. Translocations to mitigate the effects of fragmentation and habitat loss are common, but few are rigorously evaluated, particularly for fishes. Over six years, we translocated 1215 individuals of four species of imperiled fish isolated below a barrier on the San Juan River, Utah, USA, that restricts access to upstream habitat. We used re‐encounter data (both passive integrated transponder tag and telemetry detections and physical recaptures) collected between 2016 and 2023, to inform a spatially explicit multistate mark–recapture model that estimated survival and transition probabilities of translocated and non‐translocated individuals, both below and above the barrier. Individuals of all four species moved large (>200 km) distances upstream following translocation, with the maximum upstream encounter distance varying by species. Results from the multistate mark–recapture model suggested translocated fish survived at a higher rate compared with non‐translocated fish below the barrier for three of the four species. Above the barrier, translocated individuals survived at similar rates as non‐translocated fish for bluehead sucker (Catostomus discobolus) and flannelmouth sucker (Catostomus latipinnis), while survival rates of translocated endangered Colorado pikeminnow (Ptychocheilus lucius; mean, 95% CI: 0.75, 0.55–0.88) and endangered razorback sucker (Xyrauchen texanus; 0.86, 0.75–0.92) were higher relative to non‐translocated individuals (Colorado pikeminnow: 0.52, 0.51–0.54; razorback sucker: 0.75, 0.74–0.75). Transition probabilities from above the barrier to below the barrier were generally low for three of the four species (all upper 95% CI ≤ 0.23), but they were substantially higher for razorback sucker. Our results suggest translocation to mitigate fragmentation and habitat loss can have demographic benefits for large‐river fish species by allowing movements necessary to complete their life history in heterogeneous riverscapes. Further, given the costs or delays in providing engineered fish passage structures or in achieving dam removal, we suggest translocations may provide an alternative conservation strategy in fragmented river systems.

Estimating migration timing and abundance in partial migratory systems by integrating continuous antenna detections with physical captures.

Many populations migrate between two different habitats (e.g. wintering/foraging to breeding area, mainstem-tributary, river-lake, river-ocean, river-side channel) as part of their life history. Detection technologies, such as passive integrated transponder (PIT) antennas or sonic receivers, can be placed at boundaries between habitats (e.g. near the confluence of rivers) to detect migratory movements of marked animals. Often, these detection systems have high detection probabilities and detect many individuals but are limited in their ability to make inferences about abundance because only marked individuals can be detected. Here, we introduce a mark-recapture modelling approach that uses detections from a double-array PIT antenna system to imply movement directionality from arrays and estimate migration timing. Additionally, when combined with physical captures, the model can be used to estimate abundances for both migratory and non-migratory groups and help quantify partial migration. We first test our approach using simulation, and results indicate our approach displayed negligible bias for total abundance (less than ±1%) and slight biases for state-specific abundance estimates (±1%-6%). We fit our model to array detections and physical captures of three native fishes (humpback chub [Gila cypha], flannelmouth sucker [Catostomus latipinnis] and bluehead sucker [Catostomus discobolus]) in the Little Colorado River (LCR) in Grand Canyon, AZ, a system that exhibits partial migration (i.e. includes residents and migrants). Abundance estimates from our model confirm that, for all three species, migratory individuals are much more numerous than residents. There was little difference in movement timing between 2021 (a year without preceding winter/spring floods) and 2022 (a year with a small flood occurring in early April). In both years, flannelmouth sucker arrived in mid-March whereas humpback chub and bluehead sucker arrivals occurred early- to mid-April. With humpback chub and flannelmouth sucker, movement timing was influenced by body size so that large individuals were more likely to arrive early compared to smaller individuals. With more years of data, this model framework could be used to evaluate ecological questions pertaining to flow cues and movement timing or intensity, relative trends in migrants versus residents and ecological drivers of skipped spawning.

Increased density of Bluehead Sucker larvae decreases critical thermal maximum

AbstractObjectiveStreams used by Bluehead Suckers Catostomus discobolus experience variable water temperatures of high and low extremes and extreme rates of change. Acute and chronic laboratory temperature tests have been used to develop protective thermal criteria, but these methods do not allow for testing the lethality of temperature interactions with other stressors. For instance, fish density and temperature interactions are likely to occur during low‐flow periods with high densities of fish stranded in a stagnant pool; but standard thermal tests only included one fish.MethodsWe examined the effect of two acclimation temperatures that represent field temperatures (8°C and 18°C) on hatch success and larval survival, and the critical thermal maximum (CTMax) and minimum temperatures (CTMin). We then investigated how the interaction of density (n = 1, n = 10, n = 25 fish per 2 L) and temperature influence CTMax or CTMin.ResultWe found maximum egg hatch success and larval survival at 18°C and the temperature range for Bluehead Sucker larvae at 18°C was 7.2 ± 1.6°C to 32.1 ± 2.4°C. However, when the density of the larvae was high (n = 25 per 2 L) the upper thermal limit significantly decreased by 5.9°C.ConclusionOur results indicate higher fish densities negatively affect the tolerance of the fish to increased temperature. Thus, density and temperature interactions should be considered when developing protective temperature criteria.

Reduced complexity models for regional aquatic habitat suitability assessment

AbstractGeneralizable methods that identify suitable aquatic habitat across large river basins and regions are needed to inform resource management. Habitat suitability models intersect environmental variables to predict species occurrence, but are often data intensive and thus are typically developed at small spatial scales. This study estimated mean monthly aquatic habitat suitability throughout Utah (USA) for Bonneville Cutthroat Trout (Oncorhynchus clarkii utah) and Bluehead Sucker (Catostomus discobolus) with publicly available, geospatial datasets. We evaluated 15 habitat suitability models using unique combinations of percent of mean annual discharge, velocity, gradient, and stream temperature. Environmental variables were validated with observed conditions and species presence observations to verify habitat suitability estimates. Stream temperature, gradient, and discharge best predicted Bonneville Cutthroat Trout presence, and gradient and discharge best predicted Bluehead Sucker presence. Simple aquatic habitat suitability models outperformed models that used only streamflow to estimate habitat for both species, and are useful for conservation planning and water resources decision‐making. This modeling approach could enable resource managers to prioritize stream restoration across vast regions within their management domain, and is potentially compatible with water management modeling to improve ecological objectives in management models.

SYSTEMATIC LARVAL FISH SURVEYS AND ABIOTIC CORRELATES CHARACTERIZE EXTANT NATIVE FISH ASSEMBLAGE REPRODUCTIVE SUCCESS IN THE COLORADO RIVER, WESTERN GRAND CANYON, ARIZONA

Systematic larval fish surveys increase the probability of detecting rare species and provide ecological insights for more common species that can be difficult to infer from surveys of older life-stages. To characterize the reproductive success of the extant fish assemblage in the western Grand Canyon portion of the Colorado River, we conducted systematic larval fish surveys in 2014 and 2015. The effort identified endangered razorback sucker (Xyrauchen texanus) as initiating spawning in February with a continuation through July. We collected recently hatched protolarval fish throughout the study area including the most upstream sample sites, suggesting fish spawned throughout and upstream of the study area. Our collection of a protolarval endangered humpback chub (Gila cypha) supports the hypothesis that the population increased in range within the Grand Canyon from its dramatic 2001 contraction into the Little Colorado River and suggests localized spawning. Back-calculating hatching dates indicated humpback chub began hatching in late April and continued through mid-May. Native fishes numerically dominated larval fish collections (97.6 and 99.3% for 2014 and 2015, respectively) and recruitment to the early juvenile life-stage was documented for all fish species captured except razorback sucker. Abundance, measured as catch per unit effort and frequency of occurrence, was different between years for each native species captured (n = 5). Interannual differences in abiotic factors (discharge, diel fluctuations in discharge, and water temperature) were significantly different for most months between years. A redundancy analysis, evaluating the relationship between abiotic environmental factors and catch rates, suggested both discharge and water temperature were associated with speckled dace (Rhinichthys osculus), bluehead sucker (Catostomus discobolus), and flannelmouth sucker (Catostomus latipinnis), with a positive correlation to water temperature and a negative correlation to discharge. We were unable to identify associations between abiotic factors and the endangered fishes, which may have been due to the lack of variability in those species' catch rates. Improving our understanding of the relationship between reproductive success and abiotic factors would enhance management of the system to benefit native fishes.

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.

Invasion of Virile Crayfish Faxonius virilis (Hagen 1870) in the Lower Henrys Fork Drainage, Idaho

The invasive virile crayfish Faxonius virilis (Hagen 1870) has recently been documented in the upper Snake River drainage of Idaho, but its distribution is poorly known. Our objective was to determine the presence and distribution of F. virilis in the Henrys Fork drainage of the Snake River. Sampling was conducted during summer and autumn 2018 at 30 sites located in Henrys Fork River drainage, including the major tributaries Teton River, North Fork Teton River, South Fork Teton River, and Moody Creek. We used baited minnow traps and kick nets to determine presence of F. virilis. Absence was only reported if we unsuccessfully captured F. virilis using kick nets because this technique is more effective. Faxonius virilis was detected in all five streams. We did not detect F. virilis at sites at the upstream extent of sampling. This pattern suggests that F. virilis are invading the drainage in an upstream direction. Presence of species of conservation concern (e.g., Yellowstone cutthroat trout [Oncorhynchus clarkii bouvieri Jordan and Gilbert 1883], bluehead sucker [Catostomus discobolus Cope 1871], and western pearlshell [Margaritifera falcata Gould 1850]) warrant additional research to determine the effect of F. virilis on these species.

Gene flow and species delimitation in fishes of Western North America: Flannelmouth (Catostomus latipinnis) and Bluehead sucker (C. Pantosteus discobolus).

The delimitation of species boundaries, particularly those obscured by reticulation, is a critical step in contemporary biodiversity assessment. It is especially relevant for conservation and management of indigenous fishes in western North America, represented herein by two species with dissimilar life histories codistributed in the highly modified Colorado River (i.e., flannelmouth sucker, Catostomus latipinnis; bluehead sucker, C. (Pantosteus) discobolus). To quantify phylogenomic patterns and examine proposed taxonomic revisions, we first employed double‐digest restriction site‐associated DNA sequencing (ddRAD), yielding 39,755 unlinked SNPs across 139 samples. These were subsequently evaluated with multiple analytical approaches and by contrasting life history data. Three phylogenetic methods and a Bayesian assignment test highlighted similar phylogenomic patterns in each, but with considerable difference in presumed times of divergence. Three lineages were detected in bluehead sucker, supporting elevation of C. (P.) virescens to species status and recognizing C. (P.) discobolus yarrowi (Zuni bluehead sucker) as a discrete entity. Admixture in the latter necessitated a reevaluation of its contemporary and historic distributions, underscoring how biodiversity identification can be confounded by complex evolutionary histories. In addition, we defined three separate flannelmouth sucker lineages as ESUs (evolutionarily significant units), given limited phenotypic and genetic differentiation, contemporary isolation, and lack of concordance (per the genealogical concordance component of the phylogenetic species concept). Introgression was diagnosed in both species, with the Little Colorado and Virgin rivers in particular. Our diagnostic methods, and the agreement of our SNPs with previous morphological, enzymatic, and mitochondrial work, allowed us to partition complex evolutionary histories into requisite components, such as isolation versus secondary contact.

Influence of Desert Springs on Habitat of Endangered Zuni Bluehead Sucker (Catostomus discobolus yarrowi)

ABSTRACTLocated on the southeastern part of the Colorado Plateau, the Zuni Mountains are home to the endangered Zuni Bluehead Sucker (ZBS) (Catostomus discobolus yarrowi). A 4-year study was conducted on a low-flow (<80 cm3/s) hillslope spring and intermittent stream, that are home to one of the three remaining ZBS populations. Seasonal measurements of physical and hydrochemical parameters were used to estimate the contribution of groundwater to the stream and to identify geologic and hydrologic controls for the spring discharge. Seasonal concentrations and standard deviations (s) of Mg2+ were used to determine that the spring water (5.6 mg/L; s = 0.4) and surface water up-gradient from the spring input (10.7 mg/L; s = 11.2) is from different sources. Surface water down-gradient from the spring input maintain ZBS populations and is a mixture of spring water and up-gradient surface water. Mass solution mixing was used to determine spring water contributes up to 99 percent of the down-gradient water during drier seasons. Isotopes (δD, δ18O, 3H) indicate that the spring water has been recharged primarily from snowmelt within the last 70 years, while up-gradient surface water is seasonal runoff from rain and snowmelt. Continuous monitoring of dissolved oxygen (DO) mean concentrations (up-gradient = 1.6 mg/L and down-gradient = 5.7 mg/L) indicated that surface water up-gradient from the spring input are anoxic and unable to support ZBS. Surface water down-gradient from the spring input maintain appropriate DO concentrations due to perennially discharging spring waters re-aerating downstream habitats.

Otoliths Reveal Spawning Ecology and Early Life History of Sympatric Catostomids

AbstractDifferences in spawning ecology and early life history may influence the recruitment success of three sympatric catostomids in the Colorado River basin: the Bluehead Sucker Catostomus discobolus, Flannelmouth Sucker C. latipinnis, and federally endangered Razorback Sucker Xyrauchen texanus. In the San Juan River, all three species annually produce larvae, but only Bluehead and Flannelmouth suckers regularly recruit to the juvenile phase and older. Otolith microstructure analysis can determine age, growth rates, and spawning periodicity and may elucidate possible reasons for differences in recruitment among species. Larval suckers were collected from low‐velocity habitats in the San Juan River in 2011; fish were measured, and ontogenetic phase and fish age were determined from otolith increment counts. Otolith age was used to determine hatch dates and spawning periodicity, calculate daily growth rates, and develop three candidate growth functions relating fish age and body length. Relative to Bluehead and Flannelmouth suckers, Razorback Suckers had a shorter spawning period, lower growth rate, and a higher proportion of the least developed ontogenetic phase. The small size of Razorback Suckers relative to other suckers may result in higher predation and lower prey acquisition, thus restricting their transition to more developed phases and limiting recruitment to the juvenile phase. Model ranking based on Akaike's information criterion (corrected for small sample size) was nearly identical for all growth functions. The early life history information we provide may guide flow releases in this regulated system to provide suitable backwater habitat and warmer water temperatures compatible with reproduction, growth, and survival of native catostomids, including the endangered Razorback Sucker. However, due to the limited temporal and geographic extent of samples used in this study, data presented herein are not inclusive of all conditions under which suckers may be present in the San Juan River.

Integrating PIT technology into gear evaluation in an unregulated desert tributary

Fish characteristics and behavioral response to gear influences catchability. Monitoring of native fishes including bluehead Sucker Catostomus discobolus, flannelmouth Sucker Catostomus latippinis, and the endangered humpback chub Gila cypha occurs throughout the Grand Canyon and its tributaries. To quantify species-specific conditional capture probability (p^ ; probability of capturing an individual fish being conditional on the individual occupying the site), we placed a flat plate passive integrated transponder (PIT) antenna 1.5 m downstream from a hoop net and processed fish during monitoring activities for three years (2011–2013). The capture probability was conditional on fish presence as determined by PIT tag detection from the flat plate antenna. We used logistic regression to test for effects of trap response, and a non-parametric bootstrap routine was used to evaluate differences in p^ among years and fish species. Pooled p^ was similar between humpback chub (mean = 0.10, 95% CIs = 0.04–0.20) and flannelmouth sucker (mean = 0.13, 95% CIs = 0.05–0.26), while bluehead sucker were never recaptured (p^ = 0). Integrating antennas into gear evaluation has broad implications to other systems as this approach could be used to standardize catch rate estimates among different passive entrapment gears of various sizes, and among different habitat types. Obtaining catchability estimates among gear types is useful when assessing modifications to long-term monitoring programs and key to stock assessment. Here, we integrated PIT tags and antennas into gear evaluation to quantify conditional capture probability, and provided a test-of-concept for larger, broader studies that can use the underlying principles and techniques shared in this study.

Feeding Ecology of Early Life Stage Razorback Sucker Relative to Other Sucker Species in the San Juan River, Utah

AbstractLow survival of early life stage (ELS) Razorback Sucker Xyrauchen texanus in the Colorado River basin, USA, is thought to cause a recruitment bottleneck. Conversely, two other native sucker species, the Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker C. latipinnis, successfully recruit to adulthood. To explore a potential factor leading to this survival discrepancy among species, we used museum‐catalogued specimens collected from the San Juan River, Utah, to investigate trophic resource use of co‐occurring ELS suckers. We evaluated diet diversity and composition, expecting high overlap in diets among sucker species. All species were significantly different in median SL and varied in the ranges of developmental stages present in collections, with Razorback Sucker generally being the smallest and least developed. Size differences among sampled individuals coincided with a 1.7× higher mean diet richness for Bluehead Sucker and Flannelmouth Sucker compared to Razorback Sucker. The Bluehead Sucker was the only species for which diet richness increased significantly with fish size. Discriminant function analysis was able to distinguish Razorback Sucker from the other two species based on a low frequency of occurrence of all diet items. Nine of twelve diet item categories differed significantly in frequency of occurrence among species. Bluehead Sucker and Razorback Sucker had higher mean carbon and nitrogen stable isotope ratios (δ13C and δ15N) relative to Flannelmouth Sucker, and variation in δ13C was high among individual Flannelmouth Sucker across sites. The δ13C and δ15N of Bluehead Sucker decreased significantly with fish size, but no significant relationship was found for Flannelmouth Sucker or Razorback Sucker. The confounding issue of fish size and species identity in this data set prevented us from completely isolating either of these two effects on differences in diet richness, δ13C, and δ15N. Nevertheless, differences in diet item occurrence across sizes and species reflect differences in resource acquisition among ELS suckers that might be related to recruitment bottlenecks.

Temperature—Not Flow—Predicts Native Fish Reproduction with Implications for Climate Change

AbstractHabitat alterations and introduction of nonnative fishes reduced the distributions of the Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta to less than 50% of their historical ranges. Climate change models generally predict decreased streamflows and increased water temperatures that may further affect these species. Understanding the effects of flow and water temperature on their life histories should lead to better assessments of climate change impacts on extant populations and more informed management for species conservation. Basinwide larval fish sampling and hatch dates derived from otolith daily increment counts showed that water temperature was the dominant environmental factor cueing reproduction in the upper White River basin, Colorado. Reproduction for all three species began in spring, occurring first at warmer, lower‐elevation, downstream locations and progressing upriver to higher elevations as water temperatures increased. Warmer water temperatures in tributaries initiated earlier reproductive activity compared to adjacent cooler main‐stem habitat. Presence of larvae in samples and estimated hatch dates demonstrated a distinct, predictable upstream progression of reproduction associated with warming water and clear upstream limits to reproduction for all three species. Larval presence and hatching dates revealed earlier reproductive activity in 2012 than in 2013, driven by lower flow and earlier stream warming. A regression model predicted stream temperature during fish spawning seasons under different climate change scenarios and showed expanded upstream limits of thermally suitable reproductive habitat and earlier reproduction for our study species. The long‐term implications of climate change are unknown, but managers should strive to perpetuate the valuable and relatively pristine native fish community in the upper White River drainage as a vestige of those that formerly existed throughout the Colorado River basin.

An Intermittent Stream Supports Extensive Spawning of Large‐River Native Fishes

AbstractIntermittent or ephemeral streams make up a large percentage of all stream habitats and may have significant roles in spawning, foraging, refugia, and early life history habitat for many fishes. From 2015 to 2017 we examined the use of Cottonwood Creek, an intermittent tributary in the Gunnison River basin, Colorado, by spawning Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta. We used combinations of a stream‐spanning picket weir and PIT‐tag antennae near the mouth of the creek to determine fish movement in and out of the stream, which was more effective for the suckers than for Roundtail Chub. Large numbers of suckers used the stream each year despite very different flow regimes. The timing of initial fish entry varied by 6 weeks across 3 years of study from March 17 to May 6. Immigration was only loosely and inconsistently correlated to abiotic factors (various stream temperature metrics and discharge) among years and was most heavily dependent on the presence of sufficient water in the stream to permit fish passage. Average residency times of suckers ranged from 26 to 37 d depending on year and species, and spawning fish lost 10–18% of their body weight depending on species and sex. Both sucker species displayed a high level of annual site fidelity—61–71% of fish returned the year after being tagged. Larval drift was sporadic and many larvae failed to evacuate the stream before flow ceased each year. While further research is needed to assess the overall recruitment contribution from Cottonwood Creek to the regional population, this study revealed use of an intermittent tributary by thousands of native Colorado River fishes, highlighting the importance of nonperennial waters for the completion of the life histories of some large‐river fish species.

The trophic ecology of a desert river fish assemblage: influence of season and hydrologic variability

AbstractFoodweb analyses can provide insight as to how species persist in naturally dynamic environments and how these communities may respond to anthropogenic alteration. In the remaining undammed rivers of the arid southwestern United States, it is thought that plasticity in feeding behavior allows native fishes to thrive in the context of natural fluctuations in temperature, sediment, and resource availability associated with extreme swings in season and hydrology. There have been few evaluations of this hypothesis, in part owing to the rarity of rivers that retain their natural environmental dynamics and complement of native species. We investigated the feeding ecology of the fish assemblage of one such river, the Little Colorado River, Arizona, focusing on four native species: bluehead sucker (Catostomus discobolus), flannelmouth sucker (Catostomus latipinnis), speckled dace (Rhinichthys osculus), and endangered humpback chub (Gila cypha). Over two years, we sampled fish diets in July, September, January, March, and June, encompassing turbid and clear‐water conditions across seasons. We quantified food resource contributions to fish diets in fish‐centered food webs, comparing diversity of trophic linkages and linkage‐strength distribution across time. We used ordination analyses to investigate differences in diets among species and changes in diet composition across seasons and conducted seasonal comparisons of gut fullness. We observed a high diversity of dietary items (as absolute numbers and consumer–resource ratios) within a fish assemblage that was apparently resistant to extreme and recurrent environmental variability. Fish diet diversity was ~2× that of the nearby dammed Colorado River's tailwater, and over 50% of fish‐resource linkages were weak (<1% of species’ diet). Native fishes consumed a mix of terrestrial and aquatic resources. Notably, the water column‐feeding humpback chub consumed the largest percentage of terrestrially derived food items and appeared to capitalize on food resources made available by a summer flash flood, consuming twice as much during this flood than during other seasons (based on gut fullness, corrected by estimates of food quality). Other fishes exhibited similar dietary variation. Such opportunist/generalist strategies, coupled with diverse food resources, may be important to the persistence of these and other native fishes in dynamic environments.

Frequency of Opercular Deformities in Age‐0 Native Catostomids in the San Juan River from 1998 to 2012

AbstractIn the San Juan River, the recruitment of early ontogenetic stages of federally endangered Razorback Sucker Xyrauchen texanus to subadult or adult stages is rare. Opercular deformities have been detected in larval and early juvenile Razorback Suckers in the San Juan River and were investigated as an impediment to recovery of the species. Larval and early juvenile (age‐0) native San Juan River catostomids taken from 1998 to 2012 were examined for presence of opercular deformities. The frequency and severity of opercular deformities in Razorback Suckers were compared with opercular deformities in Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker Catostomus latipinnis and with hatchery‐produced Razorback Suckers. Deformities were primarily observed in larval stages and occurred both unilaterally and bilaterally. Opercular deformities were relatively consistent among years for all three species. The frequency of opercular deformities in Razorback Suckers was more than three times higher than in Bluehead Suckers and more than five times higher than in Flannelmouth Suckers. Opercular deformities in all species were high when compared with Razorback Sucker brood stock and with wild fish in other river basins. This high rate of deformity in larvae and early juvenile San Juan River Razorback Suckers likely increases mortality and inhibits recruitment to later life stages.

Tributary Use by Imperiled Flannelmouth and Bluehead Suckers in the Upper Colorado River Basin

AbstractHabitat alterations and establishment of nonnative fishes have reduced the distributions of Flannelmouth Sucker Catostomus latipinnis and Bluehead Sucker C. discobolus to less than 50% of their historical ranges in the Colorado River basin. Tributaries are sometimes less altered than main‐stem habitat in the basin and may be important to support various life history processes, but their role in the maintenance of Flannelmouth Sucker and Bluehead Sucker populations is poorly understood. Using mark–recapture techniques, we show tributaries are important habitat for native suckers in the upper Colorado River basin and report three main findings. First, both Flannelmouth and Bluehead suckers likely respond to a thermal cue that initiates spawning movement patterns. Suckers moved into Coal Creek from the White River beginning in mid‐May of 2012 and 2013 to spawn. The majority of sucker spawning movements occurred when water temperatures in White River exceeded 11–14°C and those in Coal Creek were 2.5–4°C warmer, while flows varied between years. Second, based on PIT tag detection arrays, 13–45% of suckers showed spawning site fidelity. Sampling only with fyke nets would have resulted in the conclusion that site fidelity by native suckers was only 1–17%, because nets were less efficient at detecting marked fish. Third, most suckers of both species emigrated from Coal Creek within 48 h after being captured while suckers that were detected only via arrays remained resident for 10–12 d. The posthandling flight response we observed was not anticipated and to our knowledge has not been previously reported for these species. Remote PIT tag antenna arrays allowed for a stronger inference regarding movement and tributary use by these species than what could be achieved using just fyke nets. Tributaries are an important part of Flannelmouth Sucker and Bluehead Sucker life history and thus important to conservation strategies for these species.Received October 7, 2016; accepted March 20, 2017 Published online June 28, 2017

Comparing Efficiency of American Fisheries Society Standard Snorkeling Techniques to Environmental DNA Sampling Techniques

AbstractAnalysis of environmental DNA (eDNA) is an emerging technique used to detect aquatic species through water sampling and the extraction of biological material for amplification. Our study compared the efficacy of eDNA methodology to American Fisheries Society (AFS) standard snorkeling surveys with regard to detecting the presence of rare fish species. Knowing which method is more efficient at detecting target species will help managers to determine the best way to sample when both traditional sampling methods and eDNA sampling are available. Our study site included three Navajo Nation streams that contained Navajo Nation Genetic Subunit Bluehead Suckers Catostomus discobolus and Zuni Bluehead Suckers C. discobolus yarrowi. We first divided the entire wetted area of streams into consecutive 100‐m reaches and then systematically selected 10 reaches/stream for snorkel and eDNA surveys. Surface water samples were taken in 10‐m sections within each 100‐m reach, while fish presence was noted via snorkeling in each 10‐m section. Quantitative PCR was run on each individual water sample in quadruplicate to test for the presence or absence of the target species. With eDNA sampling techniques, we were able to positively detect both species in two out of the three streams. Snorkeling resulted in positive detection of both species in all three streams. In streams where the target species were detected with eDNA sampling, snorkeling detected fish at 11–29 sites/stream, whereas eDNA detected fish at 3–12 sites/stream. Our results suggest that AFS standard snorkeling is more effective than eDNA for detecting target fish species. To improve our eDNA procedures, the amount of water collected and tested should be increased. Additionally, filtering water on‐site may improve eDNA techniques for detecting fish. Future research should focus on standardization of eDNA sampling to provide a widely operational sampling tool.Received July 27, 2016; accepted March 8, 2017 Published online May 4, 2017

Short‐Term Passive Integrated Transponder Tag Retention in Wild Populations of Bluehead and Flannelmouth Suckers

AbstractPassive integrated transponder (PIT) tags, commonly used to individually identify fish, are assumed to not hinder survival or alter the behavior of the fish and to be retained throughout the duration of the study. While these assumptions have been verified for many species, other species have exhibited poor retention or survival, or altered behavior. In this study, we evaluated short‐term PIT tag retention and recapturability of PIT‐tagged fish in wild populations of migrating and spawning Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker C. latipinnis. We trapped fish as they entered a spawning tributary of the Gunnison River near Delta, Colorado, USA. We abdominally injected 12.5 × 2.1 mm PIT tags and externally marked 2,645 fish; another 2,660 fish were given an alternative external mark but were not PIT‐tagged. When we recaptured fish as they exited the tributary, we found a PIT tag retention rate >99% and recaptured a greater proportion of PIT‐tagged fish than of control fish for both species. We did not identify any tag loss in females, suggesting that tags were not expelled with eggs while spawning. Abdominally injected PIT tags are an effective way of marking these species.Received November 22, 2016; accepted February 26, 2017 Published online April 18, 2017

Population Characteristics and the Influence of Discharge on Bluehead Sucker and Flannelmouth Sucker

Rivers are among some of the most complex and important ecosystems in the world. Unfortunately, many fishes endemic to rivers have suffered declines in abundance and distribution suggesting that alterations to lotic environments have negatively influenced native fish populations. Of the 35 fishes native to the Colorado River basin (CRB), seven are considered either endangered, threatened, or species of special concern. As such, the conservation of fishes native to the CRB is a primary interest for natural resource management agencies. One of the major factors limiting the conservation and management of fishes endemic to the CRB is the lack of basic information on their ecology and population characteristics. We sought to describe the population dynamics and demographics of three populations of Bluehead Suckers (Catostomus discobolus) and Flannelmouth Suckers (C. latipinnis) in Utah. Additionally, we evaluated the potential influence of altered flow regimes on the recruitment and growth of Bluehead Suckers...