Robert J. Edwards

An Annotated Checklist of the Freshwater Fishes of Texas, With Keys to Identification of Species

University of Texas at Austin, University of Texas - Pan American, Texas Parks and Wildlife Department

5 – Gulf Coast rivers of the Southewestern United States

River catchments flowing into the Texas portion of the Gulf of Mexico encompass a broad geographic area, with latitude ranging from around 38°N in southern Colorado to 25°N in northern Mexico and longitude ranging from about 108°W in western New Mexico to 93°W in western Louisiana. Eleven major rivers discharge into the western Gulf of Mexico from the US, including the Rio Grande, which borders with Mexico. There are eight freshwater ecoregions within the western Gulf rivers. The climate of the region ranges markedly from humid continental in eastern Texas to humid subtropical in the south in Texas, to alpine in southern Colorado and northern New Mexico, to desert in southern New Mexico and western Texas. The rivers of the western Gulf of Mexico pass through 16 highly diverse terrestrial ecoregions, which include forests, grasslands, prairies, savannahs, shrublands, and deserts.

Conservation and status of the fish communities inhabiting the Río Conchos basin and middle Rio Grande, México and U.S.A.

The Chihuahuan Desert region contains a numberof unique aquatic environments, but with fewexceptions, these have been little studied. Because of the dearth of information aboutthese environments and because many of the fishin the region are threatened with extinction orhave gone extinct, we sampled the RíoConchos basin and adjoining aquatic habitats inthe Rio Grande to assess the status of the fishof this region. Most sites showed some degreeof human-induced impacts. A number ofpotentially threatened fish were eitherabundant at only a few sites or rare or absentthroughout the localities sampled. Withoutconcerted binational efforts to conserve thefish of the region, further deletions to thenative fish fauna will likely occur.

DISCOVERY OF A NEW POPULATION OF DEVILS RIVER MINNOW (DIONDA DIABOLI), WITH IMPLICATIONS FOR CONSERVATION OF THE SPECIES

Abstract The Devils River minnow (Dionda diaboli) has a limited distribution in Texas and Mexico. It is listed as threatened in the United States and endangered in Mexico. Recent collections in previously inaccessible locations in the headwaters of Pinto Creek, Kinney County, Texas, revealed a large population of D. diaboli. This species was found in habitats of flowing, spring-fed waters over gravel-cobble substrates, usually associated with aquatic macrophytes, but was confined to the upper segment of the creek. The confined distribution of Devils River minnow can offer valuable insight into its habitat and conservation. The future of this population might be threatened by reduced spring flows resulting from excessive pumping from the associated aquifer.

Fish biodiversity changes in the Lower Rio Grande/Rio Bravo, 1953–1996

Clearly defined changes in the fishesof the Lower Rio Grande/Rio Bravo, Texas andMexico, have been documented since 1953. Morerecent surveys show that the originalfreshwater fish fauna has been retreating fromthe lower reaches and is being replaced bybrackish and marine invaders. A total of 13localities between Colombia (Nuevo León,México) and the delta (580 km) weresurveyed, with a total fish fauna of 142species, which include native, exotic, andintruding species. Changes were analysed bylocality. These changes show a loss of themajority of freshwater species, replacement oflow to higher salinity forms. This shift isvery clear in marine invaders, with somespecies penetrating the whole areainvestigated. Those changes are morenoticeable in the lower-most localities, anddiminish upstream. Data suggest that thechanges in the basin, reflecting shifts inwhole-basin ecology, include elevatedtemperature, salinity, turbidity, and lowerrunoff levels. There are indications of higherlevels of pollution as well. Informationobtained in this study is being incorporated inan Index of Biological Integrity to appearelsewhere.

Results of an Eradication Program on the Ecological Relationships of Fishes in Leon Creek, Texas

The fishes of Leon Creek are an assemblage of opportunists with a wide spectrum of feeding habits. The relative abundance of various taxa changed following a rotenone treatment designed to reduce genetic contamination of an endemic (Cyprinodon bovinus) by an introduced exotic (C. variegatus). Except for green sunfish, each fish (and a Gambusia hybrid swarm) was reestablished and is predicted to resume its role in the ecosystem in the near future. The introduction of Cyprinodon variegatus (sheepshead minnow) into Leon Creek and its subsequent hybridization with and extensive genetic contamination of Cyprinodon bovinus (Leon Springs pupfish) resulted in the recommendation for efforts to eradicate the exotic genetic material by rotenone treatment (Kennedy 1977; Echelle et al., ms). Our participation emphasized a study of the impact of the program on the other fishes inhabiting Leon Creek. Much of the literature on this creek has been devoted to Cyprinodon bovinus, a fish with its range restricted to Leon Creek. The first report on fishes in Leon Creek (actually Leon Springs approximately 22 kilometers northwest of the extant population) was of the 1851 samples by J. H. Clark, who obtained Cyprinodon bovinus and Gambusia nobilis (Girard 1859). Subsequent collections at Leon Springs contain other fishes that are likely to have been stocked. Minckley and Arnold (1969) alluded to a bovinus-like Cyprinodon that had been collected from downstream Leon Creek, but the first published reports of other fishes were by Hubbs and Echelle (1972), Echelle and Miller (1974), and Kennedy (1977), who report Cyprinus carpio (carp), Gambusia geiseri (largespring gambusia), Gambusia nobilis (Pecos gambusia), Gambusia affinis (mosquitofish), Lucania parva (rainwater killifish), Fundulus kansae (plains killifish), and Lepomis cyanellus (green sunfish) as

Threatened fishes of the world: Dionda diaboli Hubbs & Brown, 1956 (Cyprinidae)

Common name: Devils River minnow. Conservation status: Listed as threatened by the U.S. Fish and Wildlife Service 1999. Identification: Darkly outlined scales above the lateral stripe give a cross-hatched appearance. Also with a black spot on the caudal fin base that is often wedgeshaped, a black lateral stripe through the eye and onto the snout, and double dashes along the lateral line. Adults typically 30–40 mm SL. Drawing by Robert G. Howells. Distribution: Type locality is Baker’s Crossing on the Devils River, Val Verde County, Texas (Hubbs & Brown 1956). It is known to occur in Texas in the Devils River, San Felipe Creek and Sycamore Creek, Val Verde County. Extirpated from Las Moras Creek, Kinney County (Garrett et al. 1992). There are also historic records of occurrence in two small streams in Coahuila, Mexico, the Rio San Carlos and Rio Sabinas. Because no collections have been made there since the early 1970s, their current status in Mexico is unknown but, at best they are thought to be rare (Miller 1978). Abundance: The Devils River minnow has a spotty distribution within its range. At various times it has been relatively abundant (Hubbs & Brown 1956, Harrell 1978), yet at other times exceedingly rare (Garrett et al. 1992). Habitat and ecology: Little is known of the life history of the species and habitat specificity is not known. Often found in association with spring outflows and adjacent to aquatic macrophytes and may inhabit a microhabitat associated with the interface between spring runs and the river (Hubbs & Garrett 1990). Reproduction: Likely to spawn in the spring with non-adhesive and demersal eggs, similar to traits reported for D. serena (Hubbs 1951). Threats: Populations appear to have become reduced in number and size in recent history (Garrett et al. 1992). Reasons for this decline are not known, although remaining populations are potentially threatened by loss of habitat through reduced spring flows, reduction in water quality and predation and competition with exotic species. However, since little is known of the life history requirements or the ecological interactions of the Devils River minnow, it is difficult to properly assess threats or fully implement recovery actions. Conservation action: A Conservation Agreement was developed in 1998 among the Texas Parks and Wildlife Department, the City of Del Rio and the U.S. Fish and Wildlife Service and is designed to foster research to ‘eliminate or significantly reduce the probability that potential threats to the minnow will actually harm this species and to recover populations of the minnow to viable levels’. A critical subset of the range of D. diaboli is now owned by the Texas Parks and Wildlife Department and the Nature Conservancy of Texas. Conservation recommendation: The conservation actions and recommendations listed in the Conservation Agreement should be fully implemented in order to ensure survival of the species. Further research on the ecological requirements of this species is especially warranted.

Threatened Fishes of the World: Gambusia nobilis Baird & Girard, 1853 (Poeciliidae)

Common name: Pecos gambusia. Conservation status: Gambusia nobilis is listed as federally endangered by the United States (U.S. Fish and Wildlife Service 1970) and endangered by the states of New Mexico and Texas. Identification: The Pecos gambusia is a relatively robust Gambusia, with a caudal peduncle depth that is approximately two-thirds of the head length. The margins of the scale pockets are outlined in black and the dorsal fin has a subbasal row of spots. Females have a prominent black area on the abdomen that surrounds the anus and anal fin (Hubbs & Springer 1957). Drawing by Robert G. Howells. Distribution: Gambusia nobilis was described by Baird & Girard (1853) from Leon and Comanche springs, Pecos County, Texas. Leon Springs was later designated the type locality (Hubbs & Springer 1957). The species is endemic to the Pecos River basin in southeastern New Mexico and western Texas. At present, the species is restricted to four main areas, two in New Mexico and two in Texas. Abundance: Where suitable habitats exist, Pecos gambusia populations can be dense, ranging from 27 000 to 900 000 individuals in the isolated environments in which they occur (Bednarz 1979, U.S. Fish and Wildlife Service 1983). Habitat and ecology: Pecos gambusia usually inhabit stenothermal springs, runs, spring-influenced marshes (ciénegas), and irrigation canals carrying spring waters (Echelle & Echelle 1980). One or two other Gambusia may also be found in association with G. nobilis but these segregate by habitat (Hubbs et al. 1995). Pecos gambusia feed relatively non-selectively, consuming a diversity of food types (Hubbs et al. 1978). Reproduction: Gambusia nobilis produce live young. Bednarz (1979) reported an average of 38 embryos in the Blue Spring females and Hubbs (1996) found that newborns from Texas populations ranged between 35 and 50 mg with interbrood intervals of 52 days. Hybrids between G. nobilis and G. affinis or introduced G. geiseri are occasionally found, especially in habitats where one of the species is rare (Hubbs & Springer 1957). Threats: Pecos gambusia face severe threats from spring flow declines and habitat modifications throughout their range and from competition with G. geiseri. Conservation action: A recovery plan for G. nobilis has been developed (U.S. Fish and Wildlife Service 1983). Efforts have been made to improve habitat in the Balmorhea area including constructing a small refugium canal and an artificial ciénega in Balmorhea State Park, and a 110-m refugium canal at Phantom Spring. A renovation of the Diamond-Y Draw in 1998 removed G. geiseri from that system. Conservation recommendation: The recommendations in the Pecos gambusia recovery plan should be implemented and additional efforts need to be directed to the recently failing Phantom Spring system.

New Species of Gambusia (Cyprinodontiformes: Poeciliidae) from Del Rio, Texas

Abstract Gambusia clarkhubbsi (San Felipe Gambusia) is described from San Felipe Creek, a spring-fed Rio Grande tributary in Del Rio, Texas. The new species is distinguished from other members of the Gambusia nobilis species group by a combination of morphometric and pigmentation characters. It appears to prefer thermally consistent spring flows and is apparently most common in edge habitats adjacent to flowing waters.

Threatened Fishes of the World: Cyprinodon elegans Baird & Girard, 1853 (Cyprinodontidae)

Common name: Leon Springs pupfish. Conservation status: Endangered by the U.S. Fish & Wildlife Service 1980. Identification: Caudal fin bar of moderate width; lateral bars of females typically not continuous, broken ventrolaterally; males typically lack vertical bars (Echelle & Miller 1974). Drawings by Robert G. Howells. Distribution: The type locality, Leon Springs, no longer exists due to impounding and groundwater pumping (Hubbs 1980). In 1965, Cyprinodon bovinus was rediscovered in Diamond Y Spring (Minckley et al. 1991), and the species was subsequently found in a small segment (8–10 km) of Diamond Y Draw, a flood tributary of the Pecos River approximately 15 km downstream from Leon Springs (Echelle & Miller 1974). Abundance: Extirpated from Leon Springs as early as 1938 (Hubbs 1980) and presumed extinct (Hubbs 1957). Population size in Diamond Y Draw is estimated to be less than 10 000 adults (Echelle personal communication). Habitat and ecology: Groundwater pumping reduced the flow of Leon Springs from 0.57 m3 s−1 to 0 by 1962 (Echelle & Miller 1974). Today the primary water source is Diamond Y Spring. Individuals live about 20–23 months and have a generalized diet of algae and invertebrates (Kennedy 1977). Reproduction: Sexual maturity at approximately 30 mm SL (Kennedy 1977). Spawning occurs almost year around, but peaks in July (Kennedy 1977). Peak spawning temperature is 24–29◦C (Kennedy 1977). Mate preference experiments showed C. bovinus females choose randomly between conspecific males and males of C. variegatus (Garrett 1980). Threats: Cyprinodon bovinus is at risk of introgressive hybridization with C. variegatus, which was first found at Diamond Y Draw in 1974, likely due to bait transport (Hubbs 1980). Within one year an extensive hybrid swarm existed throughout the lower segment of the creek (Kennedy 1977). There is also evidence of an additional introduction of C. variegatus in the late 1980s or early 1990s (Echelle & Echelle 1997). Additional threats include habitat alteration and pollution. Conservation action: Hybrid eradication efforts (rotenone and selective seining) took place in 1976 and 1978 and reduced genetic contamination (Hubbs et al. 1978). An electrophoretic survey detected no evidence of introgression in 1982 (Echelle et al. 1987). Genetic introgression was detected once again in 1993 and 1994, when an mtDNA and allozyme survey indicated genetic introgression in both the upper (15%) and the lower (6–7%) watercourse (Echelle & Echelle 1997). In 1998 the upper watercourse was renovated with antimycin. In 2000 the lower watercourse was renovated by intensive seining. After renovation, C. bovinus from a genetically pure captive stock at Dexter National Fish Hatchery were released into each location. Both renovation methods succeeded in reducing frequencies of non-native alleles. Most of the habitat is now owned by The Nature Conservancy of Texas, who bought the 608 ha, Diamond Y Spring Preserve in 1990. Conservation recommendation: Continued monitoring of population and genetic structure is warranted. Further releases of pupfish from Dexter National Fish Hatchery would help to insure a natural genetic structure in nature.