Razorback Sucker Research Articles

Conservation to Stem Imminent Extinction: The Fight To Save Razorback SuckerXyrauchen texanusin Lake Mohave and Its Implications for Species Recovery

Razorback Sucker Xyrauchen texanus is iconic of the plight of native “big-river” fishes of the Colorado River system of western North America. The species was historically widespread and abundant throughout the basin but has suffered substantial range reductions and population declines now characteristic of Western fishes. By the 1960s the largest remaining population was in Lake Mohave, a lower Colorado River reservoir where casual monitoring began in the mid-1950s and intensified to focus on Razorback Sucker in the late 1970s. The population then was comprised of several hundred thousand large adults, but recruitment past the larval stage was nil presumably because of predation by non-native fishes and potentially worsened by nutritional limitation. Remnant adults began to dwindle in the 1980s and were virtually gone within twenty years. An ad-hoc “Lake Mohave Native Fishes Work Group” initiated investigations to identify and understand the reasons for recruitment failure and launched an informal program to perpetuate Razorback Sucker in the reservoir. The initial goal was to establish a population of 50,000 adults in Lake Mohave, and the group developed an innovative and ultimately successful strategy in which Razorback Sucker larvae produced naturally by wild adults in the lake were harvested, reared in protected off-channel habitats, and repatriated. Demographic monitoring continued and expanded, providing annual census estimates of population abundance and trends of wild and repatriated fish. Critical genetic monitoring was initiated to track spatial and temporal diversity of harvested larvae and captured repatriates. Wild adults now are gone from Lake Mohave, but they have been replaced by a genetically diverse repatriate population of several thousand fish that spawn annually and provide larvae to continue the management cycle. However, the program is stymied by continued post-larval recruitment failure and predation losses of even the largest stocked Razorback Sucker. The program depends on stocking to maintain a repatriate population and for now has preserved the genetic legacy of the species. The species fares no better elsewhere in the basin where historical genetic diversity was lower, and, with the exception of Lake Mead, wild adults have perished and populations are maintained only by stocking of hatchery-produced fish. Naturally self-sustaining populations of Razorback Sucker are unlikely to ever again occupy the lower Colorado River mainstem and the species will remain “conservation-reliant.” A conceptual strategy that integrates use of non-native-free backwaters and the river channel has promise for this and other big-river species, and its implementation should be aggressively pursued.

Survival and growth rates of stocked razorback suckers (Xyrauchen texanus) in a wetland of the Green River, Utah

We stocked four cohorts (larvae and juveniles) of razorback suckers (Xyrauchen texanus) into a managed floodplain wetland in the middle Green River, Utah, from 2008–2009. Our objectives were to determine razorback sucker early life stage survival and growth rates in a natural wetland setting. We used fyke, trammel, and dip nets in addition to boat electrofishing to address project objectives and to recover stocked fish from the wetland for translocation to the Green River. We released 1,515 razorback suckers from this wetland into the Green River, of which 110 (7.3%) have been detected in the river since stocking. Larval razorback suckers survived when few nonnative fish were present, but none survived when many were present. Juvenile fish had high mortality during summer months. We suggest fish and bird predation as plausible sources of mortality for razorback suckers in this wetland.

Detecting Razorback Suckers Using Passive Integrated Transponder Tag Antennas in the Green River, Utah

Abstract In order to increase detections of razorback suckers Xyrauchen texanus tagged with passive integrated transponders in the upper Colorado River basin, we deployed two passive instream flat-plate antennas (33 × 68 cm) at a razorback sucker spawning location in the Green River, Utah, during spring of 2012 and 2013. Over the course of 29 d in 2012 and 90 d in 2013, the antennas detected 569 razorback suckers, 19 Colorado pikeminnow Ptychocheilus lucius, 16 flannelmouth suckers Catostomus latipinnis, and 1 bluehead sucker Catostomus discobolus. Despite extensive sampling via boat electrofishing (rafts and hard-bottom boats) and netting (fyke, trammel, and gill) in wetlands that occurred from the 1990s to present in the upper Colorado River basin, a large number of tagged razorback suckers and Colorado pikeminnow, including a fish released in 1996, were detected for the first time by our antennas. Our data indicate that the detectability of razorback suckers, and precision and accuracy of survival and population estimates might be increased significantly with the addition of data gathered by passive instream flat-plate antennas in the Green River.

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.

Tributary Spawning by Endangered Colorado River Basin Fishes in the White River

AbstractThe Green River system in the upper Colorado River basin supports populations of endangered Razorback Sucker Xyrauchen texanus and Colorado Pikeminnow Ptychocheilus lucius. Documented spawning areas for these species are few and occur mainly in the Green River main stem and the lower reach of the tributary Yampa River. Herein, we report spawning by both species in an additional Green River tributary, the White River. We documented Razorback Sucker and Colorado Pikeminnow larvae and early juveniles in a 20‐km reach of the lower White River, Utah, in 2011. Movement of hatchery‐produced Razorback Sucker adults into the White River and subsequent reproduction suggests that these fish use the system to complete important life history processes. Presence of spawning areas for two endangered fishes in the White River emphasizes the important role of tributaries for providing spawning and rearing habitat for native and endangered fishes.Received April 2, 2013; accepted July 18, 2013

Time‐series analysis reveals genetic responses to intensive management of razorback sucker (Xyrauchen texanus)

Time-series analysis is used widely in ecology to study complex phenomena and may have considerable potential to clarify relationships of genetic and demographic processes in natural and exploited populations. We explored the utility of this approach to evaluate population responses to management in razorback sucker, a long-lived and fecund, but declining freshwater fish species. A core population in Lake Mohave (Arizona-Nevada, USA) has experienced no natural recruitment for decades and is maintained by harvesting naturally produced larvae from the lake, rearing them in protective custody, and repatriating them at sizes less vulnerable to predation. Analyses of mtDNA and 15 microsatellites characterized for sequential larval cohorts collected over a 15-year time series revealed no changes in geographic structuring but indicated significant increase in mtDNA diversity for the entire population over time. Likewise, ratios of annual effective breeders to annual census size (Nb/Na) increased significantly despite sevenfold reduction of Na. These results indicated that conservation actions diminished near-term extinction risk due to genetic factors and should now focus on increasing numbers of fish in Lake Mohave to ameliorate longer-term risks. More generally, time-series analysis permitted robust testing of trends in genetic diversity, despite low precision of some metrics.

Juvenile Razorback Suckers Documented in Wetlands in the Green River, Utah

Abstract The razorback sucker (Xyrauchen texanus) is a federally-endangered, large-bodied catostomid found in the Green River, Utah, a tributary to the Colorado River. Although populations of adults in the Green River appear to be increasing through stocking, recruitment has been minimal or nonexistent for several decades. Flows in the Green River in 2011 were the fourth highest in 66 years of records. These environmental conditions were favorable for survival of young-of-year razorback suckers. The purpose of this study was to determine if wild young-of-year razorback suckers occurred during fall 2011 in wetlands in the middle Green River; such observations had not been achieved since 1996. Fyke and trammel nets, minnow traps, and seines were used to sample 15 wetlands in the middle Green River (Flaming Gorge to Desolation Canyon). A total of 18 wild juvenile razorback suckers were captured in two of the wetlands.

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.

Frequent Usage of Tributaries by the Endangered Fishes of the Upper Colorado River Basin: Observations from the San Rafael River, Utah

AbstractThe importance of main‐stem rivers and major tributaries to endangered Colorado River fishes is well documented, but the use and significance of small tributary streams remains poorly understood. Historically, these fishes probably used smaller tributaries for spawning, rearing, feeding, and refuge. Currently, the proliferation of nonnative species and altered flows may have affected tributary use by endangered fishes. In February 2008 and 2009, we installed a PIT‐tag passive interrogation array (PIA) in the San Rafael River, Utah, approximately 2 km upstream from the confluence with the Green River, and another PIA approximately 60 km upstream from the Green River confluence. Using passive detections and active captures in the San Rafael River from 2008 to 2010, we detected 15 Colorado Pikeminnow Ptychocheilus lucius, 16 Bonytails Gila elegans, 20 Razorback Suckers Xyrauchen texanus, and five “undocumented” fish. Several endangered fishes were detected on multiple occasions and across years, often moving into and out of the San Rafael River from distances up to 360 km away (range, 6–360 km). Our findings demonstrate the use and the potential importance of small tributaries and their fragile habitats to endangered fishes.Received May 13, 2012; accepted March 10, 2013

Identifying Preservation and Restoration Priority Areas for Desert Fishes in an Increasingly Invaded World

A commonly overlooked aspect of conservation planning assessments is that wildlife managers are increasingly focused on habitats that contain non-native species. We examine this management challenge in the Gila River basin (150,730km(2)), and present a new planning strategy for fish conservation. By applying a hierarchical prioritization algorithm to >850,000 fish records in 27,181 sub-watersheds we first identified high priority areas (PAs) termed "preservation PAs" with high native fish richness and low non-native richness; these represent traditional conservation targets. Second, we identified "restoration PAs" with high native fish richness that also contained high numbers of non-native species; these represent less traditional conservation targets. The top 10% of preservation and restoration PAs contained common native species (e.g., Catostomus clarkii, desert sucker; Catostomus insignis, Sonora sucker) in addition to native species with limited distributions (i.e., Xyrauchen texanus, razorback sucker; Oncorhynchus gilae apache, Apache trout). The top preservation and restoration PAs overlapped by 42%, indicating areas with high native fish richness range from minimally to highly invaded. Areas exclusively identified as restoration PAs also encompassed a greater percentage of native species ranges than would be expected by the random addition of an equivalent basin area. Restoration PAs identified an additional 19.0 and 26.6% of the total ranges of two federally endangered species-Meda fulgida (spikedace) and Gila intermedia (Gila chub), respectively, compared to top preservation PAs alone-despite adding only 5.8% of basin area. We contend that in addition to preservation PAs, restoration PAs are well suited for complementary management activities benefiting native fishes.

Genetic Variability in a Recruiting Population of Endangered Razorback Suckers from Lake Mead, Arizona–Nevada

AbstractThe razorback sucker Xyrauchen texanus once was common and widely distributed throughout the Colorado River drainage of western North America. Water development and predation by nonnative species led to a significant decrease in the species’ range and a dramatic reduction in the size of remaining populations. Here, we report analyses of mitochondrial DNA (mtDNA) and microsatellite variation in larval and adult razorback suckers from Lake Mead, one of the few locations with recent evidence of recruitment. Analysis of three temporal samples of larvae from Lake Mead yielded considerable variation, but it was significantly lower than variation in Lake Mead adults or in larval and adult samples from Lake Mohave, the largest extant population. This pattern is consistent with analyses of individual temporal samples from Lake Mohave, indicating that larvae were likely produced by a relatively small number of adults. The four adult samples spanned approximately 20 years from the early 1990s to the present. Patterns of microsatellite variation were comparable among all Lake Mead adult samples, but variation was lower than that in Lake Mohave, consistent with the smaller population size in Lake Mead. Levels of mtDNA variation in adults were significantly lower for the early 1990s and 2011 samples than for the 2002 samples. The result for the early 1990s sample was consistent with current knowledge of the Lake Mead population's dynamics; however, the reduced variation in the 2011 sample are somewhat surprising, as the Lake Mead population is thought to be expanding in size. Additional spatial and temporal sampling is essential to accurately assess levels of variation and population size of Lake Mead razorback suckers.

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.

Genetic structure within and among populations of the endangered razorback sucker (Xyrauchen texanus) as determined by analysis of microsatellites

Razorback sucker (Xyrauchen texanus) was once common and widely distributed throughout the Colorado River drainage of western North America. Water development and predation by non-native species led to significant decrease in the species’ range, and dramatic reduction in size of remaining populations. Previous analyses of mtDNA variation determined that most variation was found within locations and that haplotypes were randomly distributed relative to geography, indicating these samples represent remnants of a single, basin-wide population. In addition, both diversity and number of haplotypes declined progressively down- to upstream, consistent with geologically-recent expansion into the northern portions of the basin. Analyses of variation at 13 microsatellite loci also identified a decrease in genetic variation from down- to upstream, also consistent with the hypothesis of recent expansion. Analyses of population structure identified three distinct groups, but the majority of microsatellite variation was found within populations. Most individuals from the upper Colorado River were identified as a discrete unit. These individuals exhibited high levels of relatedness, indicating this represented an isolated group of closely related individuals. There also were significant differences between populations above and below the Grand Canyon; however, estimates of Θ were relatively low. Given nothing is known of local adaptation in this species, populations above and below the canyon should be managed as independent units; however, if numbers become too low it will be possible to translocate individuals from southern populations northward to increase levels of genetic variability and decrease relatedness within units. These results also illustrate the need for careful consideration of all available information when using molecular data in identifying units for management.

Characterization of Plasma Vitellogenin and Sex Hormone Concentrations during the Annual Reproductive Cycle of the Endangered Razorback Sucker

AbstractPopulation declines of the endangered razorback sucker Xyrauchen texanus in the Colorado River basin have been attributed to predation by and competition with nonnative fishes, habitat alteration, and dam construction. The reproductive health and seasonal variation of the reproductive end points of razorback sucker populations are currently unknown. Using nonlethal methods, we characterized the plasma hormonal fluctuations of reproductively mature female and male razorback suckers over a 12‐month period in a hatchery by measuring their vitellogenin (VTG) and three sex hormones: 17β‐estradiol (E2), testosterone (T), and 11‐ketotestosterone (KT). Fish were identified as reproductive or nonreproductive based on their body weight, VTG, and sex hormone profiles. In reproductive females, the E2 concentration increased in the fall and winter, and increases in T and VTG concentrations were generally associated with the spawning period. Mean T concentrations were consistently greater in reproductive females than in nonreproductive females, but this pattern was even more pronounced during the spawning period (spring). Consistently low T concentrations (<3 ng/mL) in adult females during the spawning period may indicate reproductive impairment. In reproductive males, spring increases in KT and T concentrations were associated with spawning; concentrations of E2 (<0.48 ng/mL) and VTG (<0.001 mg/mL) were low in males throughout the study. In addition, the E2 : KT ratio and T were the best metrics by which to distinguish female from male adult razorback suckers throughout the year. These metrics of reproductive health and condition may be particularly important to recovery efforts of razorback suckers given that the few remaining wild populations are located in a river where water quality and quantity issues are well documented. In addition to the size, age, and recruitment information currently considered in the recovery goals of this endangered species, reproductive end points could be included as recovery metrics with which to monitor seasonal trends and determine whether repatriated populations are cycling naturally.Received September 24, 2010; accepted February 18, 2011

Exercise Conditioning Decreases Downstream Movement of Pond-Reared Razorback Suckers Released Into a Stream Environment

Despite augmentation stocking efforts, wild populations of razorback suckers (Xyrauchen texanus) continue to decline. Endangered razorback suckers are commonly raised in off-channel ponds until maturity (approximately 300 mm TL) and then stocked into the Colorado River or its tributaries. After fish are stocked, they commonly move large distances downstream. We conducted an experiment to determine if downstream dispersal could be reduced through exercise conditioning. Two groups of razorback suckers, exercised and nonexercised, were released into Fossil Creek, Arizona. Prior to release, a subsample from each treatment group was tested in a laboratory flow chamber. Razorback suckers that had been exercise conditioned were able to maintain a position in the flow chamber 2 times longer and at velocities 25 cm · s-1 higher than nonexercised fish. Although the intended method of field data collection via passive-integrated-transponder (PIT) antennas and a remote communication station failed because river otters (Lontra canadensis) preyed upon the released razorback suckers, implanted PIT tags were retained in otter scat. Recovered PIT tags enabled distributional analysis, which indicated that exercised razorback suckers did not move as far downstream from the point of release as nonexercised razorbacks. Exercise conditioning may increase overall fitness of pond-reared razorback suckers, and, consequently, increase the effectiveness of augmentation stocking.

Razorback sucker recruitment in Lake Mead, Nevada–Arizona, why here?

Populations of the endangered razorback sucker (Xyrauchen texanus) have been reduced in the Colorado River during much of the last century. The inability of razorback sucker to recruit in the presence of nonnative fishes and altered flow regimes is thought to be the major factor contributing to their decline. Through funding from the Southern Nevada Water Authority and the US Bureau of Reclamation, we have conducted an ongoing razorback sucker research project on Lake Mead, Arizona and Nevada, since 1996. A major emphasis of this research has been to determine if natural recruitment was occurring in Lake Mead and identify reasons for that recruitment. Ages calculated using a nonlethal aging technique for 186 individual razorback sucker indicate the Lake Mead population is relatively young and that natural, wild recruitment has regularly occurred since the late 1970s. Comparisons of back-calculated ages of captured fish with historical Lake Mead water elevations provide evidence that a change in annual lake level fluctuations is the most likely mechanism that initiated this recruitment phenomenon. Lake level changes along with inundated terrestrial vegetation and turbidity in specific sites in Lake Mead may provide littoral nursery cover for larval and juvenile razorback sucker, allowing them to avoid predation.

TDS and selenium projections for the Las Vegas Wash, post completion of the Systems Conveyance and Operations Program (SCOP)

The Las Vegas Wash (Wash) is the primary drainage channel for the Las Vegas Valley. Flows from the tributaries are a major source of contaminants of particular concern to the Wash, mainly total dissolved solids (TDS) and selenium (Se). Treated wastewater effluent discharged to the Wash currently provides enough dilution to lower the TDS and to maintain selenium concentrations below the current 5μg/L aquatic life criteria recommended by the Unites States Environmental Protection Agency (EPA; USEPA 1987); however, the Systems Conveyance Operations Program (SCOP) was intended to take most of this treated effluent through a pipeline directly into the Boulder Basin of Lake Mead. While construction of the pipeline may have had many water quality benefits for the Las Vegas Valley and Lake Mead, the dilution benefit to the Wash will be significantly reduced, primarily affecting TDS and Se concentrations in the Wash. The Wash enters Lake Mead at Las Vegas Bay, home to the endangered razorback sucker. The concern is the increased concentration of TDS and Se to the Las Vegas Bay, which potentially would impact the razorback sucker. Using data collected by the Southern Nevada Water Authority's (SNWA) environmental monitoring and management water quality team, projections have been made for expected TDS and Se concentrations post completion of the SCOP. These projections show 2 options for managing TDS and Se concentrations on the Wash: dilution and/or treatment of the tributaries. Discharging 2.08 × 105 m3/d to the Wash provides the necessary dilution to lower Se to the target concentration of 5 μg/L but will still leave TDS levels higher than desired. Treating one or more of the major tributaries will bring both Se and TDS concentrations within targeted levels.

Survival Rates and Movement of Hatchery‐Reared Razorback Suckers in the Upper Colorado River Basin, Utah and Colorado

AbstractWe used tag–recapture data to estimate apparent survival and capture probability for 119,129 hatchery‐reared, federally endangered razorback suckers Xyrauchen texanus stocked into upper Colorado River basin streams during 1995–2005. Effects investigated included reach, year, and season of stocking; fish total length (TL) at time of stocking; survival in the first year after stocking versus in subsequent years; and sampling effort. Recapture data were also used to describe poststocking movement. First‐year survival rate for stocked razorback suckers of average TL (252.5 mm) was low: 0.05 (95% confidence interval [CI], 0.042–0.071). Total length at stocking and first‐year survival were positively correlated; survival approached zero for fish smaller than 200 mm TL but increased to 0.75 or higher for the few fish larger than 500 mm. Season of stocking had a large effect on razorback sucker first‐year survival; the predicted rate for average‐length fish stocked in summer was less than 0.02 (CI, 0.012–0.022), but it was 0.07 (0.044–0.094), 0.08 (0.057–0.100), and 0.08 (0.057–0.118) for fish stocked in spring, autumn, and winter, respectively. The overall subsequent‐year survival rate for razorback suckers was estimated to be 0.75 (CI, 0.688–0.801). Capture probabilities were relatively low, ranging from 0.002 to 0.128 for fish of average TL. The mean minimum distance traveled, elapsed time, and rate of travel by razorback suckers between recaptures were 54.7 km (range, 0–514.9 km), 254 d (0–3,164 d), and 0.87 km/d (0–55.37 km/d), respectively. Movement was more frequent out of Colorado and Gunnison River stocking reaches (36.9%; range, 30.1–100%) than Green River stocking reaches (7.7%; range, 2.9–10.3%). Our recommendations include ceasing summer stocking, performing cost ‐benefit analyses of increasing TL at stocking, employing a standardized stocking protocol, and developing a comprehensive razorback sucker monitoring program, implementation of which should enhance recovery prospects for razorback suckers in the upper Colorado River basin.

Predation of Adult Razorback Sucker and Bonytail by Striped Bass in Lake Mohave, Arizona—Nevada

We report 2 separate records from sport-fish anglers in Lake Mohave, Arizona—Nevada, that document the presence of endangered razorback sucker Xyrauchen texanus and bonytail Gila elegans in stomach contents of large (13 kg) nonnative striped bass Morone saxatilis. These records suggest that striped bass, since their first appearance in Lake Mohave nearly 3 decades ago, may have played a role in population declines of the other 2 species. Current native-fish stocking programs at Lake Mohave continue to face significant obstacles to achieving population recoveries because all life stages of repatriated individuals, including mature adults, are vulnerable to predation.

The 1962 Rotenone Treatment of the Green River, Wyoming and Utah, Revisited: Lessons Learned

AbstractThe 1962 rotenone treatment of the Green River in southwestern Wyoming and northeastern Utah was planned to depress populations of undesirable fish species, primarily common carp (Cyprinus carpio), before closure of Flaming Gorge Dam (1962), and upstream Fontenelle Dam (1964). Pre‐treatment surveys catalogued fish and aquatic insect communities, distributions of native and introduced fishes, and aquatic habitat. Near‐term, post‐treatment evaluations documented the effects of rotenone treatment on the aquatic fauna. Long‐term, post‐treatment assessments gauged development of sport fisheries for introduced rainbow trout (Oncorhynchus mykiss) and followed the status of native fishes and aquatic insect fauna. Fisheries biologists planned the project because the two dams would alter the river system to the disadvantage of native, big‐river fish such as razorback sucker (Xyrauchen texanus) and Colorado pikeminnow (Ptychocheiius lucius). Further, nuisance species, such as common carp introduced in the Green River system in the late nineteenth century, would benefit from the new lentic habitats. After‐project work showed that rotenone treatment depressed nuisance nonnative fishes and that none of the native big‐river fish populations were eliminated. Post‐treatment studies showed that native fish populations were far more impacted by impoundment than by the rotenone treatment. Careful pre‐treatment planning and well‐handled application of rotenone accomplished project objectives without eliminating native fishes.