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Clear Creek Gambusia Scientific Name: Gambusia Heterochir Federal Status: Endangered, 3/11/67 • State Status: Endangered

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Clear Creek Gambusia Scientific Name: Gambusia Heterochir Federal Status: Endangered, 3/11/67 • State Status: Endangered Clear Creek Gambusia Scientific Name: Gambusia heterochir Federal Status: Endangered, 3/11/67 • State Status: Endangered Description greater temperature fluctuations. tolerant of variable water tempera- The Clear Creek gambusia is a small, This habitat is less suitable for the tures. These eurythermal (wide tem- stocky fish, about 1.2 to 1.3 inches in spring-dwelling Clear Creek gambu- perature tolerance) organisms soon length, with a metallic sheen. Scat- sia, and more suitable for the western overwhelmed the springrun animals tered dark markings on some scales mosquitofish (Gambusia affinis), a that were not isolated upstream from form distinctive crescent-shaped pat- major competitor. the first dam (Dam 1). terns. Unlike some other Gambusia Since the only habitat for the species, this fish has no speckling on Life History Clear Creek gambusia exists upstream the tail or yellow pigment on the dor- The Clear Creek gambusia is vivipa- from Dam 1, this dam is vital for pro- sal or anal fins. Females have a pro- rous (bears living young). Once fer- tecting an environment isolated from nounced anal spot, especially when tilized, females can store sperm for invasion by the western mosquitofish. pregnant, and males have a deep several months, and they may pro- In 1979, Dam 1 was in serious disre- notch at the top of the pectoral fin. duce several broods of young from pair due to age, the effects of tunnel- Like other live-bearers, the male’s March through September. Factors ing by nutria (a large introduced anal fin is modified into a tube-like such as day length, temperature, and rodent), and the expansion of root structure called a gonopodium for food availability have been shown to systems of trees. Hybridization transferring sperm to the female. influence reproductive success. between the Clear Creek gambusia The Clear Creek gambusia is and western mosquitofish had closely associated with coontail occurred in the vicinity of the dam. (Ceratophyllum sp.), an aquatic plant, This hybridization problem was the and an endemic amphipod (small crustacean), Hyalella texana. The plant supports the amphipod, which in turn serves as a primary food source for the fish. Other fishes inhabiting the Clear Creek Gambusia upper pool include the roundnose © TPWD Glen Mills minnow (Dionda episcopa) and the greenthroat darter (Etheostoma lep- Habitat idum). These small fishes The Clear Creek gambusia is restricted do not compete with the to the springfed headwaters of Clear Clear Creek gambusia Creek, a tributary of the San Saba because of different food River in Menard County in central preferences and feeding locations. Texas. This fish was first discovered Maintenance of submerged aquatic in February, 1953. Upper Clear plants, which provide protective cover Creek consists of a series of lime- from predators such as bass and sun- stone springs (Wilkinson Springs) fish, is important for both the Clear originating from the Edwards Trinity Creek gambusia and its prey. Aquifer. Prior to 1890, a low, result of mosquitofish juvenile earthen-concrete dam was built about females moving to the upper pool 80 yards downstream from the head- Threats and Reasons through damaged portions of the springs. In the 1930s, three addi- for Decline dam. If allowed to continue, tional dams were built downstream Originally, Clear Creek was a clear hybridization and competition from from the original dam, ponding water springrun that flowed freely for the western mosquitofish may have to the base of each dam. Extensive about 3 miles to its confluence with eliminated the Clear Creek gambusia. collecting of fish in 1956 and 1957 the San Saba River. Most or all of the In the summer of 1979, Dam 1 was showed that the Clear Creek gambu- creek was probably inhabited by rebuilt, securing the upper pool habi- sia was restricted to the springfed springrun species such as the Clear tat for the Clear Creek gambusia. uppermost pool. This area, about Creek gambusia and associated plants In 1985, researchers found an 2.5 acres in size, provides clear and animals. A series of dams, the increased number of Clear Creek gam- spring water of constant temperature first one built in the 1880s and the busia downstream from the recon- and low pH (slightly acidic), with others during the 1930s, were con- abundant aquatic vegetation. Below structed to provide irrigation to culti- structed dam. Soon after the dam the first dam, the habitat changes vated fields. The resulting changes in abruptly, with higher pH (more alka- habitat encouraged population line), different vegetation, and buildup of plants and animals more Clear Creek Gambusia 1 was rebuilt, rainwater killifish (Luca- avoid reduction in recharge to the nia parva) were found in Clear Creek aquifer. Limestone aquifers are vul- below the dam. This fish is not nerable to pollution and measures to native to the Edwards Plateau and prevent aquifer contamination are may have been released into Clear urged. Land managers can help by Creek by someone discarding leftover implementing sound range manage- bait. Rainwater killifish and western ment practices designed to protect mosquitofish, although not closely vegetative cover, improve range con- related, are very similar with respect dition, and prevent soil erosion and to food habits, habitat preferences, runoff. Good vegetation management and tendency to move seasonally to will help to ensure optimum aquifer areas of warmer water. Thus, rainwa- recharge and the continuous flow of ter killifish compete directly with Wilkinson Springs and others like it. western mosquitofish. Reduction in Since competition and/or Clear Creek spring the numbers of western mosquitofish hybridization with closely related or © Gary Garrett apparently allowed the Clear Creek introduced species is a major threat gambusia to survive in greater num- to endangered fishes, never release bers below the upper dam. fish into natural waters from which Finally, the continued existence they didn’t originate. Although an of the Clear Creek gambusia depends exception occurred in the case of the on continued flow of Wilkinson rainwater killifish at Clear Creek, Springs. Protection of the Edwards- beneficial impacts resulting from Trinity recharge zone is essential. introductions of exotic species are Any changes which reduce water flow the exception and not the rule. or deteriorate water quality in Finally, you can support the Spe- Wilkinson Springs could have disas- cial Nongame and Endangered Species trous consequences for the Clear Conservation Fund by purchasing a Creek gambusia. stamp, available at the Texas Parks and Wildlife Department (TPWD) Recovery Efforts headquarters in Austin or at most Continuous monitoring is ongoing to State Parks. Part of the proceeds detect factors that may affect the Clear from the sale of these items is used Biologists using a seine net to sample fish © Gary Garrett Creek gambusia population and deter- to conserve habitat and provide infor- mine the current genetic status of the mation concerning rare and endan- population. The owners of Wilkinson gered species. Springs have been instrumental in protecting the species’ habitat. Provid- For More Information ing information to landowners and the Contact general public concerning habitat Texas Parks and Wildlife DTexas requirements for rare and endangered Parks and Wildlife Department fishes is an important part of the Wildlife Diversity Branch recovery process. 4200 Smith School Road Austin, Texas 78744 How You Can Help (512) 912-7011 or (800) 792-1112 Area landowners can help by protect- or ing the groundwater of the Edwards- U.S. Fish and Wildlife Service Trinity Aquifer. Do what you can as Ecological Services Field Office an individual to conserve water and 10711 Burnet Road, Suite 200 prevent pollutants from entering the Austin, Texas 78758 aquifer. Care should be taken to (512) 490-0057 References Edwards, R.J., and C. Hubbs. 1985. Temporal changes in the Gambusia heterochir x G. affinis Hybrid Swarm Following Dam Reconstruction. USFWS, Albuquerque, New Mexico. 31 pp. U.S. Fish and Wildlife Service. 1980. Clear Creek Gambusia (Gambusia hete- rochir) Recovery Plan. USFWS, Albuquerque, New Mexico. 29 pp. 2 Clear Creek Gambusia Funds for the production of this leaflet were provided by the U.S. Fish and Wildlife Service, under Section 6 of the Endangered Species Act..
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