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13:30 | Forgotten Secrets of Invasive Fish Eradication ABSTRACT. Prior to the widespread use of rotenone as a tool for eradication of invasive fishes, extensive research was conducted on other chemical methods for removal of aquatic nuisance species. Most of this 1950’s to 1960’s research was quickly forgotten by biologists and managers as rotenone became the tool of choice for use in fish renovation projects. I evaluated two of these forgotten methods (pH manipulation using soda ash and oxygen depletion using sodium sulfite) for their effectiveness at eradicating invasive Green Sunfish, Lepomis cyanellus. Effective dosages for both chemicals were quantified in the laboratory followed by field trials conducted in two small research ponds. Soda ash was dispensed at 0.95 g/L to rapidly increase pH to >10.5. This sudden change in pH was effective at removing all Green Sunfish from two small ponds with pH returning to baseline conditions within 4 days. Sodium sulfite dispensed at 0.8 g/L rapidly decreased dissolved oxygen to < 1 mg/L causing fish to gulp at the surface and allowing them to be captured with a hand net. These tools may have advantages over other fish removal methods in that water quality conditions quickly return to baseline conditions (<48 hours for sodium sulfite and <96 hours for soda ash) with no harmful residues or other negative environmental impacts. Additional tools for control of invasive aquatic species are sorely needed and although these particular tools may only be effective in small isolated bodies of water, the addition of any new tool for invasive fish management is helpful in the ongoing battle to prevent extinctions of southwestern native fishes. |
13:45 | Drought Cues Induce Dispersal in an Aquatic Beetle, Haliplus punctatus (Coleoptera: Haliplidae) ABSTRACT. Desert-dwelling aquatic invertebrates possess a wide array of behavioral adaptations that allow them to survive harsh and highly variable environmental conditions. Dispersal and burial are two opposing behaviors that have been observed during droughts, but it is unclear which of the many drought-associated environmental cues trigger these behaviors. We investigated this question in a little-studied species of crawling water beetle, Haliplus punctatus. These small beetles inhabit arid-land aquatic habitats with hydroperiods ranging from permanent ponds to temporary streams. They are able to bury and disperse between sites, making them ideal model organisms for examining behavioral responses to extreme environmental conditions. We conducted a fully factorial experiment in which we recorded burial and dispersal behaviors in H. punctatus in response to three levels of three drought-associated environmental variables: temperature (8, 16, and 24°C), conductivity (111, 705, and 2868μS/cm), and evaporation (to 0.5, 1.5, and 2.5cm water depth), for a total of 27 treatments with 10 beetles in each treatment. We observed that neither conductivity nor evaporation affected beetle behavior. Temperature affected both burial and dispersal, although in opposite directions. Beetles were more likely to disperse at high temperature, and bury at low temperature. These observations suggest that beetles have multiple, opposing behavioral strategies that can both be triggered by changes in temperature. Given predictions of more extreme summer temperatures across the North American deserts, our results suggest that we may expect to see more dispersal of crawling water beetles in the future. |
14:00 | Biogeochemical Analyses of Airborne Deposition of Lead (Pb) Contamination in Aravaipa Creek, Arizona. ABSTRACT. The fish community of Aravaipa Creek, Arizona, with seven native species, is considered the foremost remnant assemblage of the imperiled Gila River basin fauna. In 2009, the Klondyke mine tailings were capped with a two-foot clean soil cover and installation of erosion protection on the upstream pile. Previous studies of lead isotopic ratios (208Pb, 207Pb, and 206Pb) of sediments, water and biota in pre-remediation and post-remediation of a mine tailing EPA Superfund site found remediation was effective in curtailing the inputs of contaminants into Aravaipa Creek from sediment and water. However, there was not an observed shift in the biota isotopic signatures of the lead sources. In this study we examine lead contamination in livers and muscles of native fish species, Catastomus insignis, Pantosteus clarki and Gila robusta, pre- and post-remediation with lead levels in livers much lower post-remediation. Muscle tissue was found to have lower levels of lead contamination than livers. However, given there is not a shift in fish lead isotope ratios suggests an alternative source of lead, such as airborne dust, impacting the creek. We assessed spatial patterns of airborne deposition in epilithic lichens in Upper Aravaipa Creek versus Lower Aravaipa Creek to determine spatial differences in airborne lead deposition. Mean lead found in lichens from Upper Aravaipa Creek (19.6 +/- 7.4 ppm dry), near mine tailings, was significantly greater than mean lead values from lower Aravaipa Creek (14.2 +/- 4.8 ppm dry). These data support the hypothesis that lead is entering the biotic food chain via airborne deposition via dust in Upper Aravaipa Creek that is near mine tailings but not in lower Aravaipa Creek, 15 miles downstream where mine tailings are not present. |
14:15 | Effect of Diurnal Flow Variability on Water Quality Dynamics in the Effluent-Dependent Santa Cruz River ABSTRACT. The Santa Cruz River in Arizona is one of several river systems in Southwestern USA that have experienced loss of perennial flow due to groundwater pumping and drought. Along with the Gila and Salt Rivers, the Santa Cruz currently has perennial reaches that are supported by effluent discharge from wastewater reclamation facilities. The return of perennial reaches has brought back habitat for numerous aquatic and riparian taxa. Reliable flow rates are one of the crucial components that support healthy aquatic habitat. However, in the lower Santa Cruz, flow during a given 24-hour period fluctuates by more than a factor of two, dependent on timing of water use by Tucson-area residents, creating high and low flow “tides” each day. The effect of this daily flow variation on water quality conditions in this effluent-driven system is unknown. The objective of this study is to quantify physical and chemical water quality factors in the Santa Cruz River (1) temporally--during high and low flow periods and (2) spatially--along the river downstream from the effluent outfalls. Since September 2017 we have collected water quality data (DO, pH, conductivity, nutrient levels) monthly from six locations of the Santa Cruz River spaced ~2 miles apart during both high and low flow periods. Ammonia, which is potentially toxic to aquatic biota, was significantly higher during low flow than high flow conditions on average across the year. River water quality tended to improve with increasing distance from effluent outfalls. The findings of this study suggest we should sample effluent-driven systems during low flow periods in order to identify worst case water quality conditions. We hope that these results will also help us understand how effluent can be better used to restore perennial river habitats in arid climates, including habitat for native desert fishes. |
14:30 | Chichencanab, a Catastrophic Ecosystem? (Chichencanab, un Ecosistema Catastrófico?) ABSTRACT. The word “Chichenkanaab” in Yucatec Maya means “little sea” “short water” or more precisely “cut waters” as explained by local people. It consists of a very large body of water about 30 km long that is split into 8 sections in dry season. At about 30 m above sea level, it is a relatively new lacustrine ecosystem, with origins about 8,200 years BP with rapid filling related to sea level rise of the last glaciation. It experienced an extreme dry episode AD 800-1000 (Hodell, et al. 1995). It is the largest closed-basin lake in the Yucatan peninsula, with its main water body of 452 ha and 2600 to 3500 ha flooded in the rainy season. With salinity about 4 ppt and pH of 8 due to very high Calcium Carbonate and Calcium Sulfate in the form of tar and gypsum. Oxygen ranges from 3.6 to 9 ppm and conductivity is 4400 to 5500 mЅ/cm. Mean annual temperature is 25.4°C, and surface water ranges from 26-33°C. Yearly rainfall is 1,300 mm, usually with the rainy season May to September and dry season October to April. Native fishes are 7 Cyprinodon (C. beltrani, C verecundus, C. maya, C. labiosus, C. simus, C. suavium, and C. esconditus) and possibly two more undescribed, Gambusia sexradiata, plus introduced Astyanax aeneus and Oreochromis mossambicus. It is thus one of the most variable, but dependable, aquatic ecosystems, and its habitat fragmentation combined with rich benthic, planktonic, and detritic food resources were conducive to speciation. The same factors also make this habitat very difficult to analyze. It almost impossible to thoroughly sample, since most areas are out of reach and the areas where fish can be sampled represent perhaps 3% of the total area. Despite the opinions of previous researchers, after four visits under different weather conditions, the abundance and distribution of the species of this lake's species flock are considered to be stable.
La palabra "Chichenkanaab" en maya yucateco significa "mar pequeño" "agua corta" o más bien "aguas cortadas" según lo explicado por la población local, que consiste en un gran cuerpo de agua de unos 30 km de largo quedando dividido en 8 secciones en la estación seca. Aproximadamente a 30 metros sobre el nivel del mar es un ecosistema lacustre relativamente nuevo. Con sus orígenes en aproximadamente 8,200 años BP, desde el momento del rápido llenado de la depresión y relacionado con el aumento del nivel del mar de la última glaciación. Existiendo un episodio extremadamente seco para el año 800-1000 AC (Hodell, et al., 1995). También se considera este lago como la cuenca cerrada más grande de la península de Yucatán con 452 hectáreas en su masa de agua principal con 2600 y más de 3500 hectáreas de área inundable en época de lluvias. Con una salinidad de aproximadamente 4 ppt y un pH de ocho debido al muy alto contenido de sulfato de calcio y carbonato de calcio en forma de sarro y yeso. El oxígeno varía de 3.6 a 9 ppm, conductividad entre 4400 a 5500 mЅ / cm. La temperatura media anual es de 25.4 ° C y la temperatura del agua superficial varía entre 26 y 33 ° C. Lluvia anual de 1.300 mm con la temporada de lluvias de mayo a septiembre, y una estación seca de octubre a abril generalmente. Con siete especies de Cyprinodon coexistentes (C. beltrani, C. verecunus, C. maya, C. labiosus, C. simus, C. suavium, C. esconditus) y posiblemente otras dos formas no descritas, además de la coexistencia de Gambusia sexradiata, y se introdujeron Astianax aeneus y Oreochromis mossambicus. Haciendo de este uno de los ecosistemas acuáticos más variables, pero confiables que ha conducido a la especiación debido a su abundancia de presas bentónica, planctónica, detritus y alevines como recursos dietéticos y partición del ecosistema, el cual es muy difícil de analizar debido a su tamaño y complejidad, por lo que es casi imposible hacer un muestreo representativo ya que la mayoría está fuera de alcance, y las áreas para recolectar peces no representan ni siquiera un 3% de la misma. Después de cuatro visitas en diferentes condiciones climáticas, la abundancia y distribución de las especies de esta parvada se consideran estables en contraste a las opiniones de otros investigadores. |
14:45 | Intraspecific Response of Sonora Suckers to Consecutive Wildfire Disturbances ABSTRACT. With the increasing size, frequency and intensity of wildfires across the American Southwest, assessment of wildfire effects on native fish populations is needed to better identify critical steps in recovery following these disturbances. Two large, contiguous wildfires in consecutive years (2011 and 2012) burned >100 km2 in the upper Gila River basin, New Mexico. Our objective was to quantify how occupancy and growth of juvenile and adult Sonora Suckers, Catostomus insignis, were influenced by these large fires to help develop a timetable of recovery for this species. Fish populations were sampled in June and October at five sites throughout the basin before fires (June 2008-June 2011), during the influence of fires (October 2011-June 2013), and post fires (October 2013-October 2015) to assess the response of juvenile and adult Sonora Suckers. Growth rates were measured for age-0 fish using length frequency analysis between June and October sampling events while growth for larger juveniles (>100mm) was based on recaptures of PIT tagged fish. Juvenile frequency of occurrence was high (>0.8) throughout the basin during all years in June but varied in October samples where occurrences before the fires were high (1.0), declined during years immediately following wildfire (0.4) and recovered in post fire years (0.73). Frequency of occurrence for adult fish was high (>0.6) during all years in October but varied in June samples where occurrences before and during the years of wildfire occurrence remained relatively high (>0.8) but were absent (0.0) in years following wildfires. Average body size of age-0 fish in June was smaller at upstream sites (mean = 31.2 and 36.7 mm) compared to the most downstream site (mean = 51.6 mm) (p-value=0.003 and 0.011), but juvenile body sizes did not differ among sites in October samples (p-value=0.885). Growth for adult fish differed among years with the highest growth occurring immediately following fires, lowest during pre-fire years, and highly variable growth post-fire years. Understanding the differing responses of multiple age-classes to disturbance events can aid managers to develop better management and conservation strategies. |
15:00 | Comparative Morphometrics Analysis Among Refuge and Wild Populations of Sonoyta Pupfish Cyprinodon eremus Miller & Fuiman, 1987 (Teleostei: Cyprinodontidae). (Análisis Morfométrico Comparativo de Poblaciones de Refugio y Silvestres del Pez Cachorrito del Sonoyta Cyprinodon eremus Miller y Fuiman, 1987 (Teleostei: Cyprinodontidae)) ABSTRACT. The Sonoyta Pupfish, Cyprinodon eremus Miller & Fuiman, 1987, is an Endangered freshwater fish. It is distributed in the Northwest of Mexico and Southwest of the USA in the Sonoyta River basin and in Quitobaquito Springs. Its wild populations are threatened by anthropogenic factors, so in 1986, a refuge population was successfully established in an artificial pond in the Centro Ecologico de Sonora to be used for future management and conservation of native populations. However, it is possible that individuals modified their morphology in response to changes in environmental conditions, which could be accompanied by genetic changes due to isolation. The objective of this work was to characterize and compare the morphology of Sonoyta Pupfish individuals from the refuge population with that of individuals from the wild populations. We used traditional morphometrics with measurements following the Box Truss protocol, and Discriminant Function Analysis. Both males and females of the refuge population differed from the wild population in some characters, including having wider heads, decreased body width and depth, and lower caudal region depth. These changes could be related to the lentic environment and reproduction events. We recommend evaluating the genetic diversity and including this information in the design of management plans for the conservation of the species.
El pez cachorrito del Sonoyta Cyprinodon eremus Miller y Fuiman, 1987, es un pez en Peligro de Extinción. Se distribuye en el Noroeste de México y Suroeste de EUA en la cuenca del Río Sonoyta y en el manantial de Quitobaquito. Sus poblaciones se encuentran amenazadas por factores antropogénicos, por lo que en 1986 se creó exitosamente una población de refugio en un estanque en el Centro Ecológico de Sonora con fines de manejo futuro y conservación de sus poblaciones nativas. Sin embargo, es posible que los individuos modificaron su morfología como respuesta al cambio en las condiciones ambientales, lo que pudo estar acompañado de cambios genéticos como consecuencia del aislamiento reproductivo. El objetivo de este trabajo fue caracterizar y comparar la morfología de los individuos del pez cachorrito del Sonoyta de la población de refugio y de las poblaciones silvestres del Río Sonoyta. Se utilizó morfometría tradicional mediante el diseño de medidas siguiendo el protocolo de Box Truss y se analizaron los caracteres a partir de un análisis de función discriminante. Se encontró que la población de refugio presenta un morfotipo diferente a las poblaciones silvestres, tanto en machos como en hembras, con variaciones en algunos caracteres, como cabeza más ancha, cuerpo menos ancho y profundo y región caudal de menor profundidad. Estos cambios pueden estar relacionados al ambiente léntico en que se encuentran y a eventos de reproducción. Se recomienda evaluar la diversidad genética e incluir esta información en el diseño de planes de manejo para la conservación de la especie. |
15:15 | Effects of Body Size on Vulnerability to Predation in Juvenile Roundtail Chub Stocked in the Upper Verde River, Arizona ABSTRACT. In the upper Verde River in Arizona, Roundtail Chub, Gila robusta, populations have declined, while non-native fish populations, such as Smallmouth Bass, Micropterus dolomieu, have increased. As one effort toward population recovery, Roundtail Chub are cultured in hatcheries and then released into the upper Verde River. However, predators may target recently-released fish, thereby reducing the effectiveness of stocking programs. We used laboratory and field experiments to examine the influence of non-native Smallmouth Bass on the survival of Roundtail Chub. First, we conducted laboratory trials to determine if Smallmouth Bass gape size influenced consumption of Roundtail Chub of various sizes. Trials were initially conducted with 12 prey fish and four predators; a second set of trials was conducted using two prey fish and one predator. In these trials, Smallmouth Bass consumed chub that were as large as 64% of gape, with a mean of 39.6% gape. In a field experiment where 2,177 pit-tagged Roundtail Chub were released into the Verde River (December 2016), we used electrofishing-surveys 48 hours after release to evaluate predation on stocked fish. In this experiment, we captured and measured the gape of Smallmouth Bass that consumed Roundtail Chub. Prior to stocking, the body depths of Roundtail were measured. Through these two measurements of predator and prey, we were able to quantify the relationship between predator gape and prey body depth when stocked Roundtail Chub were consumed by Smallmouth Bass in the field. From the field experiment, we infer Smallmouth Bass consumed prey that did not exceed 71.0% of gape, with a mean of 52.4% gape. A logistic regression model determines that, when prey body-depth exceeds 75% of predator gape, the probability of survival exceeds 95%. Based on these findings, we suggest that the size of both hatchery-reared fish and existing predators at stocking locations should be considered before native fish are released into the wild to reduce predator-related mortality. |
15:30 | Comparison of Aging Structures and Life History Aspects of an Historical Population of the Roundtail Chub, Gila robusta (Cyprinidae), in the Yampa River Canyon, Colorado ABSTRACT. The Gila robusta complex includes three large, morphologically variable cyprinid species native to the Colorado River drainage. All three members of this complex, G. cypha , G. elegans , and G. robusta, historically occurred in the Yampa River Canyon of Colorado and Utah. Both G. elegans and G. cypha are federally listed as endangered, and G. robusta (Roundtail Chub) is considered either imperiled or vulnerable to extinction by all state management agencies in the Colorado River basin. In July of 1998, 1999, 2001, and 2002, we opportunistically collected Roundtail Chubs on USFWS nonnative fish removal trips on the Yampa River in Dinosaur National Park. Roundtail Chubs were still abundant at this time. Our objectives were to determine the efficacy of scales, opercular bones, and otoliths as aging structures and to describe age, growth, ages at first reproduction, and tuberculation patterns relative to reproductive stages. Based on all four years of data, we obtained interpretable annuli for 111 fish using otoliths, 91 fish using opercles, and 111 fish using scales. Scale annuli generally agreed with otolith annuli up to approximately eight years, after which scale annuli consistently underestimated opercular annuli. Opercular annuli closely agreed with otolith annuli up to 15 years before underestimating otolith annuli. Based on otoliths, the oldest fish was aged at 22+, with 7 fish exceeding 15 years. Using a linearized catch-curve, Roundtail Chub had an instantaneous mortality rate of - 0.158, corresponding to 85% survivorship. Both sexes have similar ages at first reproduction, with females showing early maturing gonadal stages at five years, and late maturing or mature gonadal stages from 8-20 years. Our July sampling likely preceded actual spawning dates given that we did not collect females with later developmental stages of ovaries (e.g., MR or RE) stages. Males showed testicular development beginning at 6 years, with mature or running ripe testes from 6 to 22 years. Both sexes develop tubercles, with the intensity and extent of tubercles on the body related to gonadal stages. The greatest tubercle development occurred in males with maturing or running ripe testes, and in females with maturing ovaries. |
15:45 | A New Las Vegas Home for the Pahrump Poolfish, Empetrichthys latos ABSTRACT. In May 2018, two-hundred and fifty adult Pahrump Poolfish, Empetrichthys latos, were released into two constructed ponds at the Las Vegas Springs Preserve in Las Vegas, Nevada. This introduction marks the first time in over fifty years that a Nevada endemic fish swims at the site of the historic Las Vegas springs. Once a lush oasis within an arid Mojave Desert landscape, the Las Vegas spring complex ceased flowing prior to 1962 due to increasing groundwater usage. Endemic to the spring complex, the Las Vegas Dace, Rhinichthys deaconi, disappeared from the system around 1957, but was not officially declared extinct until after its formal description by Miller in 1984. In the following decades, the site existed solely as a well field, providing water for the growing Las Vegas community. In 1997, however, the Las Vegas Valley Water District Board of Directors approved a plan to develop a 180-acre preserve to protect and manage the natural, cultural, and water resources of the site. The Springs Preserve opened in June 2007, and by 2010 plans were made to restore some surface water habitat within the original creek channels. The federally endangered Pahrump Poolfish was identified as a possible candidate to inhabit these ponds as it is a Nevada native species, tolerant of a broad range of water conditions, and in need of an additional refuge population. Permits for the Pahrump Poolfish were obtained in 2017 and included a Nevada Department of Wildlife Scientific Collection Permit, a U.S. Fish and Wildlife Enhancement of Survival permit, and a U.S. Fish and Wildlife Safe Harbor Agreement. The initial two ponds were completed in early 2018 and Pahrump Poolfish from an existing refuge population were introduced on May 29. By June 18, dozens of ~5-mm long larval poolfish were observed in the shallows, and by August multiple age-classes were observed throughout the ponds. Pahrump Poolfish may eventually be introduced to an additional eight ponds on the Springs Preserve property. |
16:00 | Does Increasing Food-Web Stability Mediate the Effects of Cattle Grazing in Aquatic Desert Ecosystems? ABSTRACT. Anthropogenic activities have led to habitat degradation in streams throughout much of Western North America. In particular, cattle grazing has caused a loss of riparian vegetation resulting in higher water temperatures and an increase in nutrient runoff. The effects of habitat degradation on food quality and quantity for aquatic consumers could have large implications for stream communities. Since omnivores feed at multiple trophic levels, they increase community complexity and may be resilient to altered food webs. Theoretically, this would allow them to stabilize communities in degraded habitats where resources have been reduced. To test the hypothesis that omnivores positively impact community stability in degraded habitats, I established artificial mesocosms using 1000L cattle tanks with varying levels of two disturbance factors: shade (loss of shade mimicking a degraded riparian zone) and nutrients (increased nutrients representing agricultural fertilizer inputs), and the presence or absence of the omnivorous speckled dace (Rhinichthys osculus). I compared the rate of change of community structure and ecosystem function by analyzing invertebrate biodiversity and biomass, algal biomass, and water chemistry in order to determine if dace play a stabilizing role in degraded streams. By understanding the role omnivory plays in degraded aquatic systems, we can gain insight into both the management and restoration of these ubiquitous habitats. |
16:15 | Developing YY Males to Control Nuisance Fish Populations in the Southwest SPEAKER: Chad Teal ABSTRACT. Competition and predation from nonnative fishes have had a substantial impact on native fish species in the Southwestern United States. Nonnative fish introductions have been implicated in nearly 50% of endangered species listings, second only to habitat loss. The Red Shiner (Cyprinella lutrensis) has been shown to compete with native cyprinids and other small bodied species. Green Sunfish (Lepomis cyanellus) are generalists that compete with more desirable game species and prey upon native fishes. Traditional removal efforts are usually not species specific and these efforts are rarely 100% effective. Trojan sex chromosome eradication strategies have been modeled and show the collapse of target species' populations. Efforts have begun at the University of Arizona to examine the feasibility of producing Trojan sex chromosome carrier (YY male or supermale) Red Shiner and Green Sunfish. To date, breeding and larval rearing techniques have been developed at the University of Arizona Propagation Lab. Sex reversal methods and genetic marker development have also begun. The development of trojan sex chromosome carriers (YY males) for common nuisance fish species could be useful for fisheries management. |
16:30 | Ecological Traits of Non-Native Fundulus Grandis in the Pecos River: Implications for Impacts on Native Species ABSTRACT. Non-native inland populations of Gulf Killifish, Fundulus grandis, potentially threaten native fishes in the Lower Pecos River. Recent studies of F. grandis in the Pecos have shown them to be highly piscivorous compared to coastal populations, consuming native species such as the imperiled Pecos Pupfish. Otherwise, little is known about the ecology of this species in inland systems and the potential effects on native fishes. In this study we examined reproductive characteristics, size, and age of F. grandis in the Pecos River, Texas. Fish were collected from the Pecos River near Iraan, Texas twice per month in the spring, summer, and fall. Preliminary results indicate that reproduction takes place approximately between March through August, with gonadosomatic index (GSI) of females peaking in March. This suggests that the Pecos population may have a different spawning period than that described for native F. grandis in Texas coastal habitats. However, timing of peak GSI measurements is similar to that of coastal populations. Fish collected from the Pecos ranged in size between 25.7- 143.3 (mm) total length (TL) for males and 32.3 - 148.8 (mm) TL for females. Size structure of the Pecos River population suggests that there is a higher proportion of larger individuals in the invaded system. The relatively large size and piscivorous nature of F. grandis along with the degradation of the mainstem of the Pecos River, are attributes hypothesized to promote replacement of native species by non-native invaders. Thus, this study provides a foundation for understanding the potential impacts of F. grandis in this invaded, inland system. |
16:45 | Bonytail, the Arizona Tuna? Convergence in Muscle and Tendon Anatomy in Scombrids and Gila cypha ABSTRACT. Bonytail (Gila elegans) is an Arizona native endangered species that have an unusual locomotor morphology with a shallow peduncle and crescent shaped tail. This morphology appears to have evolved as an adaptation to high flow, riverine environments and may reduce drag and increase swimming efficiency. We describe the anatomical features associated with the bones and soft tissues of the caudal peduncle region. We compared the morphology of two closely related native species, Roundtail (Gila robusta) and Humpback Chub (Gila cypha), to that of the Bonytail. We cleared and stained ten individuals from each species to measure the neural and hemal vertebral spine angles (angle the spine creates with the vertebral centra) and normalized spine lengths (spine length/standard length of fish) of the twelve vertebrae proximal to the tail. Bonytail have more acute spine angles in the caudal peduncle region when compared to Humpback and Roundtail. In the soft tissues (muscle and tendon) of the caudal peduncle, we found evidence for two (paired) lateral tendons originating at the anterior axial musculature and inserting along the hypural plates of the tail in Bonytail, which appear to be absent in the other Gila species. The volume of muscle in the peduncle region of Bonytail appears to be reduced when compared to Humpback and Roundtail. Reduced musculature and novel tendons are also seen in scombrid (tunas) fishes, where their long lateral tendons transmit force from the anterior musculature to the tail. For Bonytail, this morphology may be beneficial during historic seasonal flooding events, where a more effective swimming behavior allows them to maintain position in the current with relatively low energy expenditure. |