ABSTRACT. Severe drought is causing perennial streams to flow intermittently, presenting an unprecedented level of ecological disturbance. The loss of aquatic prey could negatively impact riparian and terrestrial species, including lizards. Because lizards play important roles in riparian food webs it is crucial to understand the cascading effects of stream drying on lizard communities. We hypothesized that perennial streams provide aquatic subsidies to lizards living in riparian areas. We predicted that lizard abundances would be greater, and that individuals within a species would grow larger and faster, along perennial streams. We quantified the abundance of lizards along three paired 100-meter perennial (wet) and ephemeral (dry) stream reaches with similar microhabitat but differing water availability in the Chiricahua Mountains of southeastern Arizona. We also measured individual growth rate during a 4-week mark-recapture study of Yarrow’s Spiny Lizard (Sceloporus jarrovii) and the Striped Plateau Lizard (Sceloporus virgatus). Aquatic insects were collected in high abundances, suggesting a potential food source for lizards along perennial streams. When considering mass at first capture, we found that S. jarrovii were larger at perennial versus ephemeral reaches (P = 0.0025) but the mass of S. virgatus did not differ among reaches (P = 0.53). Additionally, we failed to detect differences in lizard abundances between paired perennial and ephemeral reaches (P = 0.37 for S. jarrovii; P = 0.5 for S. virgatus). Low sample sizes prevented us from performing statistical analysis on the mark-recapture data. Future research should quantify trophic links between lizards and potential aquatic subsidies.

ABSTRACT. Accurate estimation of age and growth rates of fish provide vital information for fishery management. The construction of Glen Canyon Dam and subsequent release of cold hypolimnetic water from Lake Powell drastically lowered the water temperature of the Colorado River, negatively affecting the growth of warmwater native and nonnative fishes. In 2013, we began collecting Common Carp dorsal spines for aging and determining growth rates in fish captured from two locations 1) a seasonally warmed backwater upstream of Lees Ferry and 2) the mainstem Colorado River. Two biologists aged digital images of 212 Common Carp spine sections. No identifying information was included in the images. Exact agreement between the readers was poor, with only 8.1% and 27.3% agreement for Common Carp from the Lees Ferry backwater and mainstem Colorado River, respectively. Reader inconsistencies as well as recapture data from tagged fish suggests that aging warmwater fish species in a cold, relatively stable temperature regime is neither precise nor accurate. The results of our study could provide insight on the accuracy and practicality of aging warmwater native fishes of the Colorado River such as Flannelmouth Sucker, Bluehead Sucker and the endangered Razorback Sucker and Humpback Chub.

ABSTRACT. Fishes serve as keystone species in many freshwater ecosystems by modifying habitat, altering nutrient cycling, and imposing top-down effects on food webs. As a result, the important role of threatened fishes in ecosystems is often cited as a reason why they should be protected. However, it is unclear to what extent the role of many threatened fishes in ecosystem dynamics is understood. We conducted a literature review of studies of the ecosystem impacts of fishes in North America to examine whether certain species and/or regions are understudied. We found that threatened species were frequently studied at higher latitudes, but that the ecosystem role of fishes was poorly studied regardless of imperilment at lower latitudes. Taxonomically, salmonids were exceptionally overstudied relative to the number of species in North America, while many families that predominate in arid and semiarid regions were understudied (e.g., Cyprinidae, Poeciliidae, and Cichlidae) or completely unstudied (e.g., Cyprinodontidae, Goodeidae, and Atherinopsidae). We then developed an index describing the relative degree of imperilment and our understanding of the ecosystem role of the fish fauna for the freshwater ecoregions of North America. According to this index, most desert ecoregions and those of the central Mexican plateau are severely understudied despite their highly imperiled fish fauna. Future work on the ecosystem-scale importance of these threatened species will provide more concrete support for campaigns to protect them from extinction and improve management of these waterbodies.

ABSTRACT. Beavers are increasingly implemented as agents in stream restoration, though little work has shown how fish utilize beaver habitats. While beaver ponds provide many types of refugia to fish, foraging habits, habitat preference, and growth within beaver ponds remains unclear. Trout were expected to forage more within beaver ponds relative to riffles due to hypothesized greater availability of aquatic macroinvertebrates. We also hypothesized that an ample feeding source combined with a lower velocity habitat would result in higher growth for trout that use beaver ponds, and due to this we suspected trout would demonstrate a preference for beaver ponds over riffles. Through a variety of stream surveys and experiments in the Logan River watershed, we determined that there were no differences in growth, body condition, or diet between trout caught in beaver ponds and trout caught in riffles. Brown Trout were larger in beaver ponds, while Bonneville Cutthroat Trout were larger in riffles. Some trout did exhibit fidelity to beaver ponds, though riffles housed more trout per volume of stream. In this system, trout may be highly adapted to beaver-created habitats such that they can utilize both beaver ponds and riffles.

ABSTRACT. Discharge of treated wastewater and upgrades to water reclamation facilities have been instrumental in returning aquatic biodiversity and riparian habitat to the Santa Cruz River in southern Arizona. The endangered Gila Topminnow has recently recolonized effluent-dependent reaches of the river, but the long-term health effects of living in effluent and the potential for these fish to persist in effluent reaches are unknown. Using non-native Western Mosquitofish (Gambusia affinis) in the lower Santa Cruz River (Tucson, AZ) as a proxy for native topminnow, we explore the challenges of living in effluent-dominated streams, including (1) fluctuating water levels, (2) the potential for microplastics to impact diet, and (3) the effects of emerging contaminants on sexual maturation. Diurnal fluctuations in discharge of effluent create daily drying events in the lower reaches of the river, which can result in the stranding and death of fish. Furthermore, in drift samples we have found microplastic concentrations as high as 5.56 particles/m3. However, in our diet analysis on a subset of 100 mosquitofish, we only documented one ingested plastic microfiber. Fish diets were otherwise comparable to natural systems and contained a variety of prey items with chironomid larvae, pupae, and adults dominating these taxa. Finally, our preliminary analysis has revealed a mosquitofish sex ratio heavily biased towards females (10.1:1), which is higher than ratios from published studies of natural systems (4.4:1). We hypothesize this pattern could be due to estrogen compounds, which can be common in effluent-dominated systems and can inhibit the sexual maturation of males. Faced with increasing human population growth and uncertainties of climate change, effluent systems will become increasingly important sources of aquatic habitat, but further studies are needed to assess their ability to support native fishes.

ABSTRACT. There are a multitude of innovative strategies available to land managers that can help facilitate landscape-level conservation and endangered species recovery in the face of expected changes in human population growth, increasing temperature, shifting rainfall patterns, and weather extremes. A good example involves Leslie Canyon National Wildlife Refuge in Cochise County, Arizona. Here, the U.S. Fish and Wildlife Service (Service) has worked effectively with others to expand protection, conservation, and species recovery activities beyond the 2,765-acre (1,119-ha) Refuge owned by the Service, extending those efforts onto an additional 20,471-acres (8,284-ha) of privately owned land. Strategies included a combination of: 1) originally delineating an adequate Refuge acquisition boundary to provide for conservation opportunities at a watershed scale; 2) monitoring and assessing the impacts of potential groundwater withdrawal within the watershed upstream from the Refuge; 3) acquiring, holding, and maintaining conservation easements on lands within that acquisition boundary; 4) formalizing a Safe Harbor Agreement with the neighboring landowners to help implement recovery activities for six federally-listed threatened and endangered species; and 5) seeking and providing funding opportunities that help enable landscape enhancement activities such as erosion control, grassland and wetland restoration, and fish and wildlife reintroductions. The success of these cost-effective efforts serves as a model by those who desire to collaborate in conserving similarly situated landscapes.

ABSTRACT. Like many other species in the southwestern United States, Roundtail Chub, Gila robusta, is threatened by invasive species, water diversions and abstractions, and land-use change. Due to precipitous declines in range size and population number in recent decades, Roundtail Chub has been a candidate for listing under the Endangered Species Act (2009 USFWS: FWS–R2–ES–2009–0004; MO 92210530083– B2). Invasive species are likely the most significant threat to this species in the Bill Williams River basin, where the range of invasive species continues to expand while native species ranges contract. Using the gradient of invasive species prevalence as a natural experiment, our objective was to determine how negative interactions with invasive fishes such as competition or predation affect the trophic status and quality of resource use for Roundtail Chub. We identified 12 sites in the upper Bill Williams watershed that support native only, invasive dominant, and mixed native and invasive fish assemblages (n = 4 sites per assemblage type). We collected fish fin tissues, macroinvertebrate primary consumers, and algal and detrital basal resources at each site. Carbon and Nitrogen stable isotope analysis of these tissues were used to establish isotopic trophic relationships along a gradient of invasion. We used Bayesian approaches to compare the three assemblage types and examine trophic overlap using niche metrics (R package SIBER) and to examine resource use and potential predation using isotope mixing models (R package mixSIAR). Trophic area, total food chain length (nitrogen range), and basal resource use (carbon range) did not differ among the three assemblage types: native, mixed, and invasive assemblages. However, our hypothesis that competition affected resource use of Roundtail Chub populations was supported by examining niche overlap and changes in resource use between Roundtail Chub and Green Sunfish, Lepomis cyanellus. When the two species co-occurred in mixed assemblages, Roundtail Chub and Green Sunfish had 59% niche overlap. Bayesian mixing models indicated both species shifted diets when they co-occurred. Roundtail Chub and Green Sunfish had an 18% and 13% shift, respectively, away from diets dominated by riffle invertebrates (e.g. Ephemeroptera). Furthermore, mixing models that included small Roundtail Chub (< 100 mm) as a potential resource for known predatory fishes in the community estimated that Roundtail Chub made up a quarter (0.25) of Black Bullhead, Ameiurus melas, diets (95% Credible Interval (CI): 0.01 – 0.60) and over a quarter (0.29) of Green Sunfish diets (95% CI: 0.05 – 0.65). Therefore, Green Sunfish could be significant intraguild predators on young-of-year Roundtail Chub. Indicators of competition and predation from stable isotope analysis along a gradient of invasion supports other research in the Colorado River Basin, namely that invasive fishes can reduce the fitness and long-term survival and persistence of native fishes, including Roundtail Chub. Invasive species removal efforts in the current range of Roundtail Chub or removal efforts before Roundtail Chub are reintroduced into former ranges should be prioritized in light of these findings.

ABSTRACT. Endemic fishes of the arid southwestern United States have rapidly declined due to anthropogenic stressors. Identifying the habitat conditions needed by these species is critical for their successful management. Habitat suitability criteria are commonly used to conserve species of interest. Therefore, developing habitat suitability criteria for native fish species across multiple rivers permits better understanding of how different environments are occupied under various circumstances. We developed stream-specific and generalized criteria for Longfin Dace, Agosia chrysogaster, Speckled Dace, Rhinichthys osculus, Desert Sucker, Catostomus clarkii, and Sonora Sucker, Catostomus insignis across four central Arizona streams. Over 1,200 sites were sampled using pre-positioned electrofishing devices during the 2017 summer low-flow period to identify relationships among fish presence and habitat variables (depth, velocity, substrate class, capture temperature, and canopy cover). Optimal (central 50% of range used) and suitable (central 95% of range used) ranges within each habitat variable were calculated for each stream, based on the occurrence of each species. In general, Longfin Dace occupied depths of 9.00 – 54.75 cm (14.25 – 27.25 cm) velocities of 0.00 – 0.63 m/sec (0.11 – 0.31 m/sec), and substrate (modified Wentworth scale) of 0.5 – 4.3 (2.1 – 3.3). Speckled Dace occupied depths of 8.25 – 74.00 cm (17.00 – 34.25 cm) velocities of 0.00 – 0.74 m/sec (0.16 – 0.43 m/sec), and substrate of 0.0 – 4.5 (2.2 – 3.6). Desert Sucker occupied depths of 9.00 – 45.00 cm (15.25 – 25.00 cm) velocities of 0.09 – 0.72 m/sec (0.21 – 0.44 m/sec), and substrate of 1.0 – 4.6 (2.5 – 3.7). Sonora Sucker occupied depths of 9.20 – 61.40 cm (17.80 – 37.70 cm) velocities of 0.06 – 0.68 m/sec (0.15 – 0.28 m/sec), and substrate of 0.5 – 5.0 (2.4 – 3.2). Most of the generalized habitat suitability criteria for all four species did not transfer into study streams. Agencies should develop stream-specific habitat suitability criteria when managing species of interest for a certain stream.

ABSTRACT. The Devils Hole Pupfish (DHP) is a conservation icon; however, one outstanding question about this species remains unresolved: how long has it persisted in its hellish environment? Here I discuss recent estimates of the age of this species, gene flow out of Devils Hole since colonization, and future directions. We previously used RADseq data to infer the history of pupfishes in Death Valley. Instead of relicts isolated for millions of years, we found evidence for frequent gene flow among Death Valley and Amargosa National Wildlife Refuge pupfish populations and divergence coinciding with the last glacial maximum 15 kya. We estimated that Devils Hole was colonized by pupfish approximately 1 kya, followed by genetic assimilation of pelvic fin loss, and recent gene flow into neighboring spring systems. We also estimated that some pupfishes in Death Valley exhibit the lowest genetic diversity of any wild population and may display the highest mutation rates of any vertebrate, as suggested by the extreme environmental conditions and life history characteristics of DHP. These results provide a new perspective on an iconic endangered species using population genomic methods and support the idea that repeated cycles of gene flow and renewal are needed to sustain a network of small pupfish populations in the desert.

ABSTRACT. The Inyo Mountains Salamander, Batrachoseps campi (IMS), is one of only two salamanders in the world whose range is restricted to desert ecosystems. The IMS has been documented from 21 localities in the Inyo Mountains of California; all but one of these are in riparian habitat. In 2017 and 2018 I conducted intensive fieldwork on the species, to gather information for a status review by the U. S. Fish and Wildlife Service, which will determine if listing of the species under the federal Endangered Species Act is warranted. I visited 17 of the 21 documented IMS localities, and gathered data on its abundance, distribution, and basic ecology, and evaluated possible threats to the species, including the chytrid fungus, Batrachochytrium dendrobatidis. My observations suggest that although the IMS population as a whole appears reasonably healthy and currently is chytrid-free, severe flash floods occurring after 2000 have negatively impacted at least five local populations. Ongoing climate change in the Southwest could exacerbate the frequency and/or severity of future flash floods, and damage or destroy additional IMS habitat.

ABSTRACT. Devils Hole and its unique pupfish, Cyprinodon diabolis, have been historically managed in a species specific approach. Recently, more holistic, ecosystem based approaches have been used for conservation and recovery efforts for this critically endangered species. Investigations into energy flow and food web structure in Devils Hole found that carbon was limiting in winter. Stable isotope analyses indicated a year-round, fundamental source of carbon for the pupfish diet comes from allochthonous (outside sourced) plant and animal material (Wilson & Blinn, 2007, Western North American Naturalist 67(2):185-198). As late as 1950, the surrounding landscape of Devils Hole was bladed, removing the above ground and subterranean biomass encircling Devils Hole (USDOI General Land Office Report, Bureau of Land Management, 1950). Terrestrial restoration/revegetation of Devils Hole began May 2017 to increase the potential allochthonous carbon input into Devils Hole and reverse desertification. To assess the new vegetation’s effectiveness in delivering organic matter to the system, a perennial shrub abscission (litter) study was devised. Monthly collections of the highest occurring shrubs have shown an average output of .03568 g/m²/day of organic matter. Atriplex confertifolia (Shadscale) has shown the highest average output with .00991 g/m²/day and Larrea tridentata (Creosote) has shown the lowest average output with .00047 g/m²/day. Data will be compared to allochthonous funnel traps that are deployed biannually over the water surface of Devils Hole.

ABSTRACT. The extremities of desert flow regimes create unique environments for fish species throughout Arizona. This work aims to explore the relationship between the distributions of various fish species throughout time and space in four Arizona streams. We used flow statistics generated from USGS gage stations as well as USGS StreamStats estimates of flows in precise non-gaged locations to examine relationships between these flow statistics and the relative abundance of fish species in four Arizona streams. Data on fish distributions comes from an intensive summer field season (2017) as well as a 20-year dataset from a collaboration with the Arizona Game and Fish Department. This research can provide critical information to managers on how flow dynamics interact with different fish species in arid-land rivers.

ABSTRACT. Desert fishes are cryptic, and infrequently seen by the public. Apathy of the public toward these fishes and their ecosystems hinders their conservation. Fortunately, advanced technological means to acquaint the public with these species is becoming increasingly common. High-definition underwater and aerial footage are now possible with affordable and user-friendly technology. We are creating low-cost, educational videography presentations featuring the unique and often rare desert fishes of Nevada and Death Valley. In these videos, we are testing the inclusion of various widely recognized social psychology principles to maximize presentation effectiveness. Low cost technology, especially when combined with the use of easy to include psychological principles, may provide spectacular visual results and could potentially serve as an effective tool to acquaint the public with rare desert fishes. After multiple rounds of testing, viewers' knowledge significantly improved after viewing such videos, p <0.001. Here, we will present results from this research of testing the relationship between the inclusion of social psychology principles and their impact on viewers’ learning outcomes and endorsement of a “pro-ecological” world view. 

ABSTRACT. Quitobaquito spring and pond and the nearby Rio Sonoyta are some of the only perennial water bodies in the western Sonoran Desert, and support populations of endangered Sonoyta mud turtle and pupfish. Quitobaquito is fed by a near constant flow from springs, while the Rio Sonoyta holds only a few perennial pools with intermittent flow after significant rainfall. We have started a comprehensive and comparative inventory of aquatic invertebrates in Quitobaquito and the Rio Sonoyta to understand how local food webs and, as a result, populations of mud turtles and pupfish, fluctuate through time. Since April 2017, we have had four seasonal sampling events at Quitobaquito and the Rio Sonoyta: April, June, October, and January. Each sampling event targeted the dominant microhabitat types present, including the headspring, pond, and spring channel riffles, runs, and pools at Quitobaquito and river pools and intermittent riffles at the Rio Sonoyta. Although Quitobaquito and the Rio Sonoyta are geographically adjacent, species richness and community composition differed between the locations. Quitobaquito was more taxonomically rich, with 124 species, whereas Rio Sonoyta only had 75 species. Species richness changed seasonally in the Rio Sonoyta, reaching its highest level during flowing periods in spring and lowest levels in the driest part of summer. In contrast, there appeared to be no predictable seasonal changes in species richness at Quitobaquito. Invertebrate communities in the Rio Sonoyta tended to be fairly distinct from those at Quitobaquito. However, pond samples at Quitobaquito more closely resembled the community of Rio Sonoyta pools than those of the other other microhabitat types at Quitobaquito. Understanding variability in invertebrate prey communities could help us better predict the needs of the imperiled species that depend on these perennial systems. Next steps in our research include stable isotope analyses to link potential prey items to pupfish and turtle populations.

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.

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.

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.

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.

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. 

Hodell, D.A., J. H. Curtis & M. Brenner. (1995). Possible role of climate in collapse of classic Maya civilization. Nature Vol. 375 1 June 1995. pp 391-394.

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.

Hodell, D.A., J. H. Curtis & M. Brenner. (1995). Possible role of climate in collapse of classic Maya civilization. Nature Vol. 375 1 June 1995. pp 391-394.

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.

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.

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.

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.

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.

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.

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.

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.

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.