Colorado Pikeminnow Ptychocheilus Lucius Research Articles

Body condition variation in a riverine piscivore: have small non-native cyprinids benefited an endangered fish?

Relations between annual abundance of three introduced fishes and body condition of an endangered piscivore, Colorado pikeminnow Ptychocheilus lucius, in the upper Colorado River were assessed to aid prioritization of non-native fish control efforts. Relative condition (Kn: mass at a given length) was monitored during spring, 1991–2013. Positive and significant relations were found between annual mean Kn and backwater densities of two common non-native, small-bodied, cyprinid species in downstream reaches of the 293 km study area. High mean Kn in spring followed years when fall densities of fathead minnow Pimephales promelas and red shiner Cyprinella lutrensis were high. No such relation was found with a third species, sand shiner Notropis stramineus. These three species have dominated zero-velocity habitats since their introduction in the 1960s. No relation was found between mean Kn prior to spawning and subsequent abundance of Colorado pikeminnow young-of-the-year (YOY) 3 months post spawning, suggesting mean Kn was not a driver of fall YOY abundance. Based on predatory interactions with larval native fishes documented in the literature, red shiners were deemed detrimental to Colorado pikeminnow despite their food value. Sand shiners appeared benign: non-predatory and less important as food. Fathead minnows, however, might be beneficial. They appear non-predatory on fish larvae while providing an important food source for various Colorado pikeminnow life stages. Managers need to weigh these benefits when considering control efforts.

A Small Warm Tributary Provides Prespawning Resources for Colorado Pikeminnow in a Cold Dam-Regulated River

Abstract Riverine habitat mosaics, including tributaries, are an important reason the Green River subbasin supports the largest remaining population of federally endangered Colorado Pikeminnow Ptychocheilus lucius in the Colorado River Basin. Upstream Colorado Pikeminnow distribution is limited by Flaming Gorge Dam and few typically occurred in the reach immediately downstream of the dam, which is the reach most affected by thermal and hydrologic alterations. However, fish captures and passive integrated transponder (PIT) antenna sampling of previously tagged individuals from 2011 to 2021 revealed seasonal congregations of up to 75 Colorado Pikeminnow annually in the mouth of Vermillion Creek, a small tributary in the regulated reach. Approximately 11% (N = 93 individuals) of the entire 2017–2018 Green River basin population were encountered in Vermillion Creek over the 11-y study, an underestimate of use considering that untagged fish were not detected by antennas. Colorado Pikeminnow used Vermillion Creek primarily when Green River spring flows from Flaming Gorge Dam were high and cold in May through mid-June when the confluence was a large, deep backwater warmer than the main channel and supported forage fishes. Intra-annual encounters revealed seasonal residence times for individual Colorado Pikeminnow up to 91 d, and multiple inter-annual encounters indicated site fidelity. Frequent detections of individual Colorado Pikeminnow in a Yampa River spawning area soon after their detections in Vermillion Creek indicate this tributary may be an important resource for reproductive adults. The intensive and basin-wide PIT tagging and detection program for Colorado Pikeminnow enhanced our understanding of the importance of small habitat nodes such as Vermillion Creek in the Green River drainage network. Understanding and protecting these seasonally available riverine habitat mosaics used for prespawning conditioning may assist with recovery of Colorado Pikeminnow.

Otolith Microstructure Analysis Elucidates Spawning and Early Life Histories of Federally Endangered Fishes in the San Juan River

The short larval ontogenetic phase has a large impact on success or failure of fish populations due to naturally high mortality rates. Yet, for the federally endangered fishes Colorado Pikeminnow Ptychocheilus lucius and Razorback Sucker Xyrauchen texanus, information about this sensitive life stage is limited. We determined species-specific age–length functions, spawning periodicity, and environmental factors related to growth and the onset of spawning by these species in the San Juan River of the Colorado River basin. Daily ages were determined from lapillar otoliths, and growth rates were calculated for subsamples of San Juan River larval Colorado Pikeminnows and Razorback Suckers collected from 2009 through 2017 and six candidate age–length functions were fit to evaluate the relationship between age and growth. Spawning periodicity estimates from the best-fit-model and published function were compared to those from observed otolith ages and differences were analyzed. The responses of spawning periodicity and growth to abiotic and temporal conditions were evaluated. For both species, spawning dates produced by otolith ages and best-fit functions were significantly different from those produced by the published functions, but not from each other. Age–length functions determined in this study enable more accurate back-calculation of ages and prediction of spawning periodicity than published functions. The spawning periodicity estimate of San Juan River Colorado Pikeminnow and Razorback Sucker were both impacted by multiple parameterizations of temperature and discharge. For both species, fish age had the biggest influence on growth. Accurate knowledge of spawning periodicity and factors affecting fish growth can improve timing of management activities to maximize benefit to Colorado Pikeminnows and Razorback Suckers in the San Juan River.

Quantifying Consumption of Native Fishes by Nonnative Channel Catfish in a Desert River

AbstractThe establishment of nonnative predators can have devastating consequences for native fish communities, but predation rates are often difficult to quantify due to spatial and temporal variation in predator foraging behavior. Predation by Channel Catfish Ictalurus punctatus throughout the Colorado River basin potentially threatens the recovery of native fishes. Because Channel Catfish are highly opportunistic feeders, an understanding of how piscivory by this species impacts prey populations should help to guide management in invaded systems. We used laboratory observations to model temperature‐dependent stomach evacuation rates and combined those estimates with field‐collected diet data to derive annual consumption across a 152‐km reach of the San Juan River (New Mexico, Colorado, and Utah). In the field, stomach fullness increased with water temperature while the probability of observing fish prey in the diet increased with TL of Channel Catfish and water turbidity. Based on estimates of daily ration, diet composition, and Channel Catfish population demographics, we estimated the San Juan River population’s fish consumption to be 4.9 kg·ha−1·year−1 (95% CI = 4.0–6.1 kg·ha−1·year−1) in 2018 and 2.3 kg·ha−1·year−1 (95% CI = 1.8–2.8 kg·ha−1·year−1) in 2019. Native fishes accounted for 54% of the fish biomass consumed, which included two incidents of endangered Colorado Pikeminnow Ptychocheilus lucius consumption. Although these estimates should help managers to assess the predatory threat of Channel Catfish, additional information, such as the efficacy of nonnative control and prey population compensatory responses, will likely be necessary to develop robust management strategies aimed at reducing the predatory impacts of this nonnative species on native fish assemblages.

Efficacy of fluorescent calcein mark retention and identification in endangered Colorado pikeminnow Ptychocheilus lucius

AbstractDistinguishing hatchery‐reared fishes from wild conspecifics can be required to quantify the success of augmentation programmes. This study estimated the probability of identifying calcein‐marked, hatchery‐reared Colorado pikeminnow Ptychocheilus lucius Girard from external and internal structures. Both control and marked fish held in the laboratory were correctly identified 80% of the time after 300 days. A fluorometer was more accurate 180 days post‐marking, whereas visual observation was more discriminating at 300 days. There were no differences in detection rates among structures in laboratory fish, and for most structures of fish held outdoors, detection rates were <20%. Overall, a strong negative effect of light on mark persistence was observed. Also, an initial positive effect of fish size on mark fluorescence and a negative effect of fish growth were detected. These results suggest the potential use of calcein as a batch‐marking tool would be aided by future studies that better quantify light exposure and calcein mark persistence in both field and experimental settings.

A Tribute to Tributaries: Endangered Fish Distributions within Critical Habitat of the San Juan River, USA

AbstractThe extent of fish movements in contemporary river networks can depend on spatial position relative to attractive features that may provide food and refuge, such as tributary mouths, or restrictive features, such as barriers. From the San Juan River basin in New Mexico and Utah, we integrated remote summertime PIT tag detections at two tributary mouths (McElmo Creek and Chaco Wash) with main‐stem recapture data from 2012 to 2015 to determine if two endangered species, Colorado Pikeminnow Ptychocheilus lucius and Razorback Sucker Xyrauchen texanus, differed in tributary use, demography, and seasonal ranges. Razorback Suckers were more abundantly detected (n = 266 individuals) and recaptured (n = 145) than were Colorado Pikeminnows (n = 96 detected; n = 55 recaptured). Despite the San Juan River flowing uninterrupted between the tributary mouths, individuals of each species separated into tributary‐specific groups. Razorback Suckers had very similar sizes and ages at each tributary, reflecting a homogeneous augmented population. Colorado Pikeminnows separated into tributary‐specific groups of either adult (Chaco Wash) or subadult (McElmo Creek) fish based on total length and age. Analyses suggested that fish size was a significant factor explaining the extent of seasonal ranges for both species. Although the ranges of both species exhibited a tributary effect, this effect was more significant in explaining Razorback Sucker ranges than Colorado Pikeminnow ranges, which were explained best by season. Understanding how mobile species interact with attractive and inhibitive river features can help managers identify potential sampling biases along with possible consequences of spatially structured populations. Managers should consider extending sampling upstream of barriers, installing additional permanent antenna arrays, and maintaining perennial flows in these tributaries.

Age‐Specific Estimates Indicate Potential Deleterious Capture Effects and Low Survival of Stocked Juvenile Colorado Pikeminnow

AbstractHatcheries and stocking programs have become necessary to repatriate or augment populations of imperiled fishes worldwide. Over nearly two decades, millions of endangered juvenile Colorado Pikeminnow Ptychocheilus lucius have been stocked into the San Juan River (Colorado, New Mexico, and Utah); however, recruitment of these individuals to adult life stages (age ≥6) remains low. Using a mark–recapture data set collected from annual riverwide electrofishing efforts between 2003 and 2016, we investigated apparent survival and capture probabilities of stocked Colorado Pikeminnow to identify age‐specific bottlenecks contributing to this lack of recruitment. With relatively high capture rates, which averaged between 0.34 and 0.39 for the first 2 years after an individual's first encounter, our results indicated that survival was consistently less than 0.25 for young age‐groups (i.e., ages 1–3), and no appreciable increase in survival occurred until fish had been in the river for at least 3 years (i.e., age ≥4+). Although age and capture effects were confounded for most age‐groups, capture appeared to reduce apparent survival for age‐2 fish by approximately 50%. The confounding effects of age, a completely hatchery‐origin population, and extensive environmental alterations to the San Juan River make it difficult to disentangle factors associated with this overall reduced juvenile survival.

Cranial morphological scaling and relative prey size limitations for a native predator in an invaded system

Over evolutionary time, predator-prey interactions have shaped and constrained functional and behavioral traits of piscivorous fishes. The endangered Colorado Pikeminnow Ptychocheilus lucius, a large endemic piscivore of the Colorado River Basin, encounters a substantially altered prey base that differs in behaviors and morphologies compared to the historical suite of native prey. To assess physical limitations of Colorado Pikeminnow predation, we conducted a feeding experiment with two species of nonnative prey (spined and despined Channel Catfish Ictalurus punctatus and Red Shiner Cyprinella lutrensis) and quantified scaling of cranial morphology in this predator. In our predation experiments, Colorado Pikeminnow (215–312 mm total length) consumed both spined and despined Channel Catfish as well as Red Shiner but only consumed prey less than 20% of the predator’s total length. Previous feeding trials using smaller Colorado Pikeminnow, with native and nonnative prey species, indicated they consumed prey up to 35% of their total length, suggesting relative prey size limits may decrease as this predator grows. Morphological measurements also suggested relative prey size suitability may decrease as Colorado Pikeminnow become larger, with head depth and width demonstrating isometric scaling at small sizes and shifting to negative allometry as fish get larger. Together, these data suggest an ontogenetic shift in the head morphology of Colorado Pikeminnow may decrease the relative size of prey available to these predators. In severely altered systems, understanding trophic characteristics that limit overall predator resource availability will be critical for conservation of piscivorous fishes.

Long-term mark-recapture monitoring of a Colorado pikeminnow Ptychocheilus lucius population: assessing recovery progress using demographic trends

Long-term mark-recapture monitoring of a Colorado pikeminnow Ptychocheilus lucius population: assessing recovery progress using demographic trends

Patterns of fish movement at a desert river confluence

AbstractQuantifying fish movements in river networks helps identify critical habitat needs and how they change with environmental conditions. Some of the challenges in tracking fish movements can be overcome with the use of passive integrated transponder (PIT) tagging and antennas. We used PIT technology to test predictions of movement behaviour for four fish species at a mainstem–tributary confluence zone in an arid‐land river system. Specifically, we focused on the McElmo Creek tributary confluence with the San Juan River in south‐western Utah, USA. We quantified variation in species occurrences at this confluence zone from May 2012 to December 2015 relative to temporal and environmental conditions. We considered occurrences among species relative to tagging origins (tributary versus mainstem), season and time of day. Generally, fishes tagged in the focal tributary were more likely to be detected compared to fish tagged in the mainstem river or other tributaries. Additionally, adults were most likely to be detected across multiple years compared to subadults. Based on a Random Forests model, the best performing environmental variables for predicting seasonal detections included mainstem discharge during run‐off season (razorback sucker Xyrauchen texanus), tributary discharge during monsoon season (Colorado pikeminnow Ptychocheilus lucius) and mainstem water temperature (flannelmouth sucker Catostomus latipinnis and channel catfish Ictalurus punctatus). The variable responses by endemic and introduced fishes indicate tributary habitats provide several key functions within a fish community including spawning, rearing, foraging and refuge.

Evaluation of a Long‐Term Predator Removal Program: Abundance and Population Dynamics of Invasive Northern Pike in the Yampa River, Colorado

AbstractThe Northern Pike Esox lucius is invasive in the upper Green and Yampa River basins of Colorado and Utah and impedes endangered fish recovery in the upper Colorado River basin. Mechanical removal was implemented in 2004, but Northern Pike population dynamics and removal efficacy were not well understood. We analyzed mark–recapture records from 8,929 individual Northern Pike captured during 2004–2010 from three reaches of the Yampa River: Hayden to Craig (upstream reach), South Beach–Little Yampa Canyon–Juniper (middle reach), and Maybell–Sunbeam (downstream reach), encompassing 175 river kilometers. Annual survival rates for Northern Pike of the mean TL (465 mm) were highest downstream (mean = 0.54; range = 0.36–0.71) and lowest upstream (mean = 0.25; range = 0.12–0.38). Annual abundance exhibited the opposite pattern, as it was highest upstream (annual range = 1,144–4,078 fish) and lowest downstream (range = 232–746 fish). After removal occurred each year, Northern Pike abundance increased annually by nearly 1,000% in the upstream reach, over 875% in the middle reach, and over 375% in the downstream reach due to recruitment and immigration. Resulting densities were 4–58 times higher than those for a native apex predator, the endangered Colorado Pikeminnow Ptychocheilus lucius. Northern Pike movement was mostly (90%) downstream and sometimes extensive, which may have promoted establishment of additional populations. Removal rates were inadequate to reduce Northern Pike abundance in the Yampa River because recruitment and immigration exceeded removal and mortality. Investigation of reproduction and recruitment, along with source management, spawning disruption, and increased removal, are needed to further reduce Northern Pike abundance and to aid recovery of native and endangered fishes. These findings underscore the need for sustained, comprehensive, and often costly removal efforts—including evaluation of their effects—in the face of the expanding distribution and abundance of invasive predator species.Received April 16, 2015; accepted March 29, 2016Published online September 19, 2016

Fish Community Distributions and Movements in Two Tributaries of the San Juan River, USA

AbstractRecognizing how stream fish communities—and their habitats—differ across space and time relative to their position in stream networks (i.e., main‐stem versus tributary habitats) is increasingly important for the conservation of imperiled native fish communities in altered river networks such as those in the Colorado River basin. We studied the patterns (community composition) and processes (movements) that shape species occurrences and distributions in two tributaries of the San Juan River, Utah and New Mexico, between 2012 and 2014. Our results show that distance from the San Juan River was a strong driver of tributary fish community structure, whether through declines in species richness (Chaco Wash) or species turnover (McElmo Creek), and that these patterns coincided with habitat gradients (i.e., depth, substrate, and width). Occurrences of passive integrated transponder (PIT)–tagged fish at a stationary antenna in McElmo Creek just upstream of its confluence with the San Juan River varied by species but generally were associated with spring spawning migrations (Flannelmouth Sucker Catostomus latipinnis, Razorback Sucker Xyrauchen texanus), exploratory movements (Colorado Pikeminnow Ptychocheilus lucius), and monsoon flooding (Channel Catfish Ictalurus punctatus, Razorback Sucker). Occurrences of PIT‐tagged fish in Chaco Wash were dominated by endangered Razorback Suckers and Colorado Pikeminnows, suggesting that this habitat supplies useful habitat, forage, or both. Given the common occurrences of native fishes in these tributaries, incorporating these habitats into basinwide management actions seems necessary to fully understand the spatiotemporal dynamics of native and nonnative fish communities.

Movement and Growth of Juvenile Colorado Pikeminnows in the San Juan River, Colorado, New Mexico, and Utah

AbstractUnderstanding patterns of animal distribution and abundance based on their movements is important to identify the habitats and factors that maximize growth and reproductive success. Despite stocking age-0 hatchery-reared Colorado Pikeminnow Ptychocheilus lucius for over 10 years in the San Juan River of Colorado, New Mexico, and Utah, the population consists primarily of stocked juveniles; adults remain rare. We investigated seasonal movement and growth of juvenile Colorado Pikeminnows in the San Juan River from 2009 to 2012 to inform recovery efforts throughout the Colorado River basin. Our results indicated fish made long-distance upstream movements from spring to summer while moving back downstream over winter. Seasonal movements may be associated with maximizing growth along longitudinal and seasonal temperature regimes. Length-at-age relationships reveal Colorado Pikeminnows in the San Juan River were larger than individuals of the same age in other populations in the upper Colorado River bas...

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.

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

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

Thermal regime suitability: Assessment of upstream range restoration potential for Colorado pikeminnow, a warmwater endangered fish

AbstractDams have reduced distribution of the endangered Colorado pikeminnow Ptychocheilus lucius in the upper Colorado River basin: low‐head diversion dams blocked upstream passage and large dams inundated free‐flowing segments and cooled downstream reaches with deep‐water releases. To date, range restoration efforts in the Colorado and Gunnison Rivers have focused on building fish ladders around diversion dams to allow recolonization of upstream reaches. Upstream thermal suitability for this warmwater cyprinid was assessed using temperature data and existing distributional information from river reaches where Colorado pikeminnow movements were unrestricted. Among‐site thermal regime comparisons were made using mean annual thermal units (ATU), derived from mean daily temperatures during 1986–2005 and the relation between temperature and Colorado pikeminnow growth. Upstream distributional limits in the Yampa and Gunnison Rivers occurred where in‐channel thermal regimes fell below a long‐term mean of 47–50 ATU, suggesting that two Colorado River fish ladders will make available an estimated 17 km of thermally suitable habitat. A Gunnison River fish ladder successfully re‐established access to 54 km of suitable habitat, but 32 km of critical habitat upstream remains unsuitable. Suitability there could be achieved by raising temperatures only 1–2°C from late May to mid‐October with installation of a temperature control device on an upstream dam. Maximum, main‐channel, summer temperatures did not limit Colorado pikeminnow distribution in downstream reaches of the upper Colorado River. Published in 2010 by John Wiley & Sons, Ltd.

Polyphyly of the Pikeminnows (Teleostei: Cyprinidae) Inferred Using Mitochondrial DNA Sequences

AbstractThe phylogenetic relationships of the Colorado pikeminnow Ptychocheilus lucius, northern pikeminnow P. oregonensis, Sacramento pikeminnow P. grandis, Umpqua pikeminnow P. umpquae, and hardhead Mylopharodon conocephalus were examined by using molecular data to investigate monophyly of the genus Ptychocheilus. Phylogenies generated using DNA sequence data from the cytochrome b and 16S ribosomal DNA genes of the mitochondrial genome reveal that Ptychocheilus is a polyphyletic genus and suggest that the taxonomy of the group is in need of further revision. These data yield insights into the evolution of the pikeminnows and help place the significant evolutionary events in context with the geological history of parts of western North America (e.g., ancient drainage connections that may have allowed for dispersal, followed by speciation once those connections were broken).

Population Status of Colorado Pikeminnow in the Green River Basin, Utah and Colorado

AbstractCapture‐recapture sampling of 819 km of streams in the Green River subbasin, Utah and Colorado, of the Colorado River basin was conducted in 2000‐2003 to estimate population demographic parameters and recovery status for endangered Colorado pikeminnow Ptychocheilus lucius. Parameter estimates from a Huggins robust‐design, multistratum model suggested a basinwide decline in the abundance of adult (total length, ≥450 mm) Colorado pikeminnow. Reductions were most severe in the middle Green River (59%) and White River (63%), the two largest population segments. Reductions were less severe in the Yampa River (29%), Desolation‐Gray Canyon (11%), and lower Green River reaches (36%). In 2001, the first year the entire subbasin was sampled, adult Colorado pikeminnow abundance was estimated at 3,304 fish (95% confidence interval, 2,900‐3,707) but declined to 2,142 fish (1,686‐2,598) by 2003, a 35% reduction. However, accounting for a reach not sampled in 2000 makes it likely that the reduction was 48% over the 2000‐2003 period. The abundance of recruits (400‐449 mm) in the study area averaged 8.9% of adult abundance. The annual survival rate for 2000‐2003 was 0.65 (0.59‐0.71), lower than the 0.82 rate estimated for 1991‐1999; mortality exceeded recruitment. The few captures and lack of recaptures of fish of at least 800 mm suggest that apparent survival was low for large Colorado pikeminnow. The reduced abundance of adult Colorado pikeminnow was due, in part, to the weak year‐classes of age‐0 fish produced in the 1990s and the reduced survival of recruits and adults in 2000‐2003. Based on these results, downlisting of this species is not warranted at this time. Better understanding of the factors that influence adult survival rates, abundance dynamics, and the recruitment of early life stages as well as the effects of flow recommendations and nonnative predaceous fishes would assist the conservation of Colorado pikeminnow.

Mitochondrial DNA Variation in the Endangered Colorado Pikeminnow: A Comparison among Hatchery Stocks and Historic Specimens

AbstractThe Colorado pikeminnow Ptychocheilus lucius is a federally endangered species restricted to the Colorado River. Dexter National Fish Hatchery and Technology Center, Dexter, New Mexico, maintains three separate captive stocks of the Colorado pikeminnow: 1974YC (Yampa River), 1981YC (Green–Colorado rivers), and 1991YC (Colorado River). We surveyed mitochondrial DNA diversity in these three stocks (879 base pairs [bp]; ND‐4L and ND‐4 genes; N = 30) and in museum specimens collected from 1890 to 1976 (450 bp; ND‐4; N = 11). All individuals had the same haplotype except for a 1‐bp variant detected in 2 of the 12 fish from 1981YC. The low variation is postulated to be the result of a post‐Pleistocene bottleneck in the wild and small sizes of the hatchery founder populations.