ASPECTS OF THE LIFE HISTORY OF THE SAN FELIPE GAMBUSIA, GAMBUSIA CLARKHUBBSI: HABITAT UTILIZATION PATTERNS

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1 ASPECTS OF THE LIFE HISTORY OF THE SAN FELIPE GAMBUSIA, GAMBUSIA CLARKHUBBSI: HABITAT UTILIZATION PATTERNS Aspectos de la historia de vida del Gambusino de San Felipe, Gambusia clarkhubbsi: Patrones de utilización del hábitat. ROBERT J. EDWARDS* AND GARY P. GARRETT Department of Biology, University of Texas-Pan American, Edinburg, TX 78541(RJE) HOH Fisheries Science Center, Texas Parks and Wildlife Department, Ingram, TX (GPG). *Correspondent: ABSTRACT--We investigated the habitat use of the San Felipe gambusia (Gambusia clarkhubbsi) and the sympatric Tex-Mex gambusia (G. speciosa) using seines and minnow traps in their natural habitats in San Felipe Creek, Val Verde County, Texas. Seines were used in two contrasting mesohabitat types and minnow traps were used in various habitats in a smaller area to test the habitat utilization of Gambusia in areas of moderate versus low flow environments as well as habitats with or without dense vegetation. We also conducted a series of experiments using artificial streams that mirrored these environment types. While there appeared to be a consistent trend of obtaining G. clarkhubbsi in sparsely vegetated habitats next to sources of swiftly flowing water and G. speciosa inhabiting sparsely vegetated, backwater areas in the winter and spring, G. clarkhubbsi was found in greater abundance than G. speciosa in dense vegetation regardless of flow regime. It also appeared that the young of the introduced armored catfish, armadillo del rio, Hypostomus sp., moved into the sparsely vegetated, flowing water areas in the summer, displacing G. clarkhubbsi from those habitats. The artificial stream experiments provided results similar to the minnow traps with respect to dense versus sparse vegetation utilization among the two species, but the artificial stream experiments were not consistent with the seining or minnow trap utilization patterns found with respect to flow, suggesting that other factors may also be involved in the habitat segregation of these species. Key words: Gambusia clarkhubbsi, San Felipe Creek, Texas, habitat use, ecological segregation, invasive species RESUMEN Se investigaron los entornos del guayacón de San Felipe (Gambusia clarkhubbsi) y guayacón de Nuevo León (G. speciosa) mediante el uso de chinchorros y de trampas o nasas de carpita en sus entornos naturales en el arroyo San Felipe, condado de Val Verde, Tejas. La tendencia del G. clarkhubbsi fue constante en los entornos de poca vegetación y agua corriente. La misma tendencia se observó con G. speciosa en entornos de poca vegetación como también en áreas de remanso en invierno y primavera. Se observó que los jóvenes del siluro armado, Hypostomus sp., introducidos a entornos de poca vegetación y agua corriente desplazaron los G. clarkhubbsi de sus entornos durante la época de verano. Trampas de carpita fueron utilizadas en varios entornos para probar la presencia del Gambusia y contrastar áreas de ambiente moderado, ambientes de bajo flujo de agua y entornos con o sin vegetación densa. También se condujo una serie de experimentos usando corrientes artificiales. Estos proporcionaron resultados similares tales como el uso de trampas de carpita en vegetación densa en contraste con vegetación escasa entre las dos especies. Los resultados sugieren que otros factores pudiesen también influir en la segregación del entorno de estas especies. Palabras clave: Gambusia clarkhubbsi, Río San Felipe, Texas, uso de habitat, segregación ecológica, especies invasivas. INTRODUCTION The San Felipe gambusia (Gambusia clarkhubbsi) was described in 2003 from specimens obtained from San Felipe Creek, Val Verde Co., within the city limits of Del Rio, Texas (Garrett and Edwards, 2003). The species was described as a member of the G. nobilis species group which includes a number of spring-adapted Gambusia in central and west Texas and New Mexico (Rauchenberger, 1989) and is most closely related to Gambusia krumholtzi found several hundred kilometers downstream in an isolated Rio Grande drainage in Mexico (Minckley, 1963). Although numerous collections of fishes had been taken in San Felipe Creek and other streams in the nearby area, the new species was only first collected in late 1997 (Girard, 1859; Peden, 1973; Garrett et al., 1992; Garrett and Edwards, 2003) and has only been found in a limited area below the main springs. Little is known concerning the life history of this new species, yet its limited range and relative rarity led to its being petitioned to become a federally Endangered species in

2 2005. It is the purpose of this study to better document various ecological factors affecting the abundance of the species. We investigated aspects of the habitats that are used by the San Felipe gambusia and compared these to habitats used by the sympatric Tex-Mex gambusia, Gambusia speciosa. We also used a series of large artificial streams located in central Texas to test how well these can model the abundance patterns found in nature with respect to flow and vegetation requirements of the two sympatric species. San Felipe Springs were originally the fourth largest spring system in Texas (Brune, 1981), but it is now the third largest since the larger Goodenough Springs, located to the west, was inundated by Amistad Reservoir in This reservoir has created greater head pressure on the springs located to the immediate east, including San Felipe Springs. San Felipe Creek flows through a city of nearly 40,000 residents, beginning at a series of small springs several km north of the city and augmented by the main springs at the north end of the city. These are used as the source of the city s water supply, and the spring-run downstream flows through a golf course, a series of city parks and residential areas. There is an approximately 2.5 m high dam located below one of the city parks (Lion s Park) which impounds water for approximately 1 km upstream. Some of the creek has been diverted into an old irrigation canal network (Acequia Madre canal) below the headsprings. The city s waste treatment effluent enters the creek downstream from the most populated urban area and the creek then flows an additional several kilometers to its confluence with the Rio Grande. San Felipe Creek is also the habitat of 3 federal or state listed Threatened species: proserpine shiner, Cyprinella proserpina; Devils River minnow, Dionda diaboli and Rio Grande darter, Etheostoma grahami. MATERIALS AND METHODS In order to determine the influence of water flow on habitat use of the two species of Gambusia, we sampled using a 5-m seine above and below the dam at Lion s Park on 26 June 2002, 30 December 2002, 21 and 22 July 2003, 17 July 2004, 25 March 2005, 13 July 2005, and 27 December The area sampled above the dam was in a constructed concrete backwater used as a children s swimming area in the Lion s Park. The water depth was uniformly 0.5 m in depth and the sides were composed of rock ledges and steps, the lowermost were covered by a depth of approximately 0.1 m of water. Below the dam we sampled along the western wall of the dam in a quiet-water area surrounded by a riffle area on the downstream side and water rushing over the dam on the upstream side. The substrate in this area was generally devoid of vegetation and consisted of a limestone shelf. In each area, fishes were collected for a period of

3 approximately 15 minutes and all specimens, except the state or federally listed species, were preserved, taken to the laboratory and counted. In all cases, listed species were counted and returned unharmed to the creek. A second series of experiments were carried out to detect the combined influence of vegetation with varying flows. We used minnow traps in the afternoon of 13 July 2005 and in the morning of 14 July 2005, and in the afternoon of 27 December 2005 and in the morning of 28 December 2005 in the children s swimming area in Lion s park and in the immediate upstream area of the impounded creek, in an area with stone-constructed stream-bank walls with a sinuous appearance. This physical attribute provided a number of areas with higher and lesser flows and some habitats were heavily vegetated while others were relatively devoid of vegetation. Traps were baited with Gravy Train brand dry dog food and placed in a variety of habitats for a period of 2 hours. Fishes were then preserved, taken to the laboratory and counted. Four experimental artificial streams with alternating riffles and pools were also used to test the habitat preferences of G. clarkhubbsi and G. speciosa. These systems were located at the HOH Fisheries Science Center and each artificial stream consisted of six pools (1,136-liter round tank, 183 cm diameter and 90 cm tall) and five riffles (183 x 47 x 38 cm troughs). Two different vegetation regimes (none or dense) and two flow regimes (slow or fast) were used in the four units. Vegetation was removed from two of the artificial streams using Reward brand herbicide (2 oz. per system) on 1 October 2004 and these systems also were treated with an algicide 10 days later. Flows were varied in the 4 units by using 1 pump creating flow of approximately 14,400 L/hr in 2 of the units simulating low flows and using 2 pumps, with approximately twice the flow, in each of the other 2 units to simulate high flows. On 20 October 2004, 25 G. clarkhubbsi and 25 G. speciosa were added to each of the four artificial streams and all Gambusia were identified to species and counted on 9 November RESULTS A total of 2,384 Gambusia was captured by seining in the flowing water area below the dam and 1,581 Gambusia were taken in the backwater children s swimming area (Fig. 1). In the winter and spring samples taken at the station with flowing water, the relative abundance of G. clarkhubbsi approximately 60% of all Gambusia captured and G. speciosa accounted for approximately 40% (Fig. 1a). Although there was a significant difference between the two Gambusia in the winter (X 2 = 33.8, 1 df, P < 0.001), both winter and spring samples showed greater numbers of G. clarkhubbsi than G. speciosa in these environments. However, in our

4 summer samples, G. speciosa dominated, accounting for about 63% of the Gambusia captured and G. clarkhubbsi for approximately 37% (X 2 = 111.6, 1 df, P < 0.001). We noted a large increase of young introduced armored catfish (Hypostomus sp.) in the area we seined in the summer and these made up nearly 18% of all fishes captured. These catfish were observed in clusters of several to dozens of fish on the shelf where most Gambusia clarkhubbsi were taken in other seasons and are presumed to have been displaced by the larger, armored catfish. Twelve other fish species also were captured incidentally during our seining in the area below the dam including: central stoneroller, Campostoma anomalum; goldfish, Carassius auratus; proserpine shiner, Cyprinella proserpina; manantial roundnose minnow, Dionda argentosa; Devils River minnow, Dionda diaboli; Texas shiner, Notropis amabilis; Mexican tetra, Astyanax mexicanus; yellow bullhead, Ameiurus natalis; longear sunfish, Lepomis megalotis; Rio Grande darter, Etheostoma grahami; Rio Grande cichlid, Cichlasoma cyanoguttatum and blue tilapia, Oreochromis aureus. In the backwater habitat, the two species of Gambusia were nearly the only species present. Gambusia speciosa accounted for approximately 70% of all fishes taken in all collections, while G. clarkhubbsi accounted for approximately 25% of the fishes captured. The relative abundances of the two Gambusia appeared relatively consistent throughout the year (Fig. 1b) and the differences were significant (Winter/Spring X 2 = 67.1, 1 df, P < 0.001; Summer X 2 = 276.5, 1 df, P < 0.001). This habitat was much less diverse than the area sampled near flowing water, and only 4 other species were taken in low numbers in the backwater including, D. argentosa, N. amabilis, A. mexicanus and, O. aureus. The fishes captured in the minnow traps were allocated to 4 flow and vegetation categories to correspond to the same flow and vegetation regimes of the artificial stream experiments and trap data were pooled from all traps (Fig. 2a). A total of 3,093 Gambusia was captured in the traps; 1,570 G. clarkhubbsi and 1,523 G. speciosa. The only other fish that was captured in the traps was A. mexicanus. In the traps placed in dense vegetation, G. clarkhubbsi accounted for nearly 60% of the Gambusia captured. In traps placed in areas with observable, moderate flows but no vegetation, approximately equal numbers of both Gambusia species were found. However, traps set in non-vegetated, backwater areas, without apparent flows contained approximately 70% G. speciosa and only 30% G. clarkhubbsi. The number of G. clarkhubbsi in the 4 artificial streams grew from a total of 100 at the beginning of the experiment to 718 at the end of the year-long experimental period. During the same interval, the 4 experimental treatments of 100 total G. speciosa grew to a total of 954 (Fig 2b). Both species maintained roughly equal densities in all four of the vegetation and flow

5 regimes with the exception of the sparsely vegetated, high flow habitat where G. speciosa became approximately 2.5 times more abundant than G. clarkhubbsi. In comparison with the equivalent environmental conditions with the minnow traps, the artificial stream low flow with sparse vegetation treatment (X 2 = 5.3, 1 df, P < 0.02) and the high flow with sparse vegetation treatment (X 2 = 7.4, 1 df, P < 0.007) were significantly different with respect to the overall proportions of the two Gambusia species. DISCUSSION In the non-vegetated, backwater habitats, G. speciosa dominated the Gambusia relative abundance in both the seining and minnow trap collections by approximately the same percentage abundance. But, while the relative abundance of G. clarkhubbsi was greater than that of G. speciosa in all but the summer collections in the sparsely vegetated, flowing water habitat below the dam, the relative abundances of the 2 species of Gambusia were more equal in the minnow traps set in the impounded area of the creek. We attribute this to the lesser flows in the impounded region relative to the much swifter flows found below the dam. Thus, G. clarkhubbsi seems to dominate in sparsely vegetated habitats next to sources of swiftly flowing water and G. speciosa prefers sparsely vegetated, backwater areas in the winter and spring. Regardless of flow regime, G. clarkhubbsi was found in greater abundance than G. speciosa in dense vegetation. The habitat utilization of G. clarkhubbsi in the quiet waters near moving water habitats is nearly identical to that of the now extinct San Marcos gambusia, G. georgei, in the San Marcos River in central Texas (Hubbs and Peden, 1969; Edwards et al. 1980). The large numbers of G. clarkhubbsi found associated with dense vegetation was also similar to the results found by Hubbs et al. (1995) for the Endangered Pecos gambusia, G. nobilis, in the Balmorhea State Park refugium canal. The experimental units did not clearly track the data obtained from minnow traps in the creek in all given conditions. In order to isolate the effects of only flow or vegetation, we pooled the trapping and artificial stream data into the 2 flow regimes and the 2 vegetation regimes (Fig. 3). When these data were pooled, G. clarkhubbsi was more abundant than G. speciosa in the dense vegetation while G. speciosa was more abundant in the sparse vegetation. In the minnow traps set in higher flows, G. clarkhubbsi had a slight dominance, while G. speciosa had a slight dominance in traps set in low flows. In the artificial streams, these results were reversed. Gambusia clarkhubbsi had a slightly greater abundance in the low flow units while G. speciosa had a greatly increased abundance in the higher flow units. Since absolute flows varied within

6 the pools and riffle artificial stream microhabitats and in San Felipe Creek, it may be that flow and vegetation are only a subset of a larger number of factors influencing the habitat utilization of the two sympatric Gambusia, especially G. clarkhubbsi. Our lack of statistically significant, demonstrable differences in our artificial stream results point out the need for additional studies on this rare and unique species. We thank D. Edwards, T. Edwards, M. Edwards, and L. Garrett for their help in the field collections and the Texas Parks and Wildlife Department s HOH Fisheries Science Center staff for their assistance in the artificial stream experiments conducted at the HOH Fisheries Science Center. LITERATURE CITED BRUNE, G Springs of Texas. Vol. I. Branch-Smith, Inc., Fort Worth, Texas. 566 pp. EDWARDS, R. J., E. MARSH AND C. HUBBS The status of the San Marcos gambusia, Gambusia georgei. Endangered Species Report No. 9, U.S. Fish and Wildlife Service, Albuquerque, New Mexico, 34 pp. GARRETT, G. P. AND R. J. EDWARDS New species of Gambusia (Cyprinodontiformes: Poeciliidae) from Del Rio, Texas. Copeia 2003: GARRETT, G. P., R. J. EDWARDS AND A. H. PRICE Distribution and status of the Devils River Minnow, Dionda diaboli. Southwestern Naturalist 37: GIRARD, C Ichthyology of the boundary. U.S. and Mexican Boundary Survey, 3:1-85, pls HUBBS, C., A. E. ECHELLE AND G. DEVINE Habitat partitioning by two congeners (Gambusia geiseri and Gambusia nobilis) at Balmorhea State Park, Texas. Texas Journal of Science 47: HUBBS, C. AND A. E. PEDEN Gambusia georgei sp. nov. from San Marcos, Texas. Copeia 1969: MINCKLEY, W. L A new poeciliid fish (genus Gambusia) from the Rio Grande drainage of Coahuila, Mexico. Southwestern Naturalist 8: PEDEN, A. E Virtual extinction of Gambusia amistadensis n. sp., a poeciliid fish from Texas. Copeia 1973: RAUCHENBERGER, M Systematics and biogeography of the genus Gambusia (Cyprinodontiformes: Poecilidae). American Museum Novitates 2951:1-74.

7 Figure 1. Comparison of habitat utilizations of San Felipe gambusia (G. clarkhubbsi) and Tex-Mex gambusia (G. speciosa) in contrasting flow environments obtained by seining. Shown are the relative abundances of the two gambusia in (a) a sparsely vegetated habitat next to flowing water and (b) a sparsely vegetated habitat in a backwater habitat without discernible flow. Also shown in the moving water habitat is the relative abundance to all fishes captured of the introduced armored catfish, Hypostomus sp.

8 Figure 2. Comparison of habitat utilizations of San Felipe gambusia (G. clarkhubbsi) and Tex-Mex gambusia (G. speciosa) in each of the contrasting flow and vegetation regimes taken by minnow traps in San Felipe Creek and in artificial stream experiments used to simulate these environments. Shown are (a) the relative abundances of each gambusia in the minnow traps and (b) the relative abundances of each gambusia at the end of the artificial stream experiment.

9 Figure 3. Comparison of habitat utilizations of San Felipe gambusia (G. clarkhubbsi) and Tex-Mex gambusia (G. speciosa) in high or low flow or in dense or sparse vegetation regimes taken by minnow traps in San Felipe Creek and in artificial stream experiments used to simulate these environments. Shown are (a) the relative abundances of each gambusia in the minnow traps and (b) the relative abundances of each gambusia at the end of the artificial stream experiment. Data have been pooled from the individual traps and treatments to isolate the differences of only flow and vegetation.