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Big Bend gambusia

The Big Bend gambusia (Gambusia gaigei) historically occurred in the outflow of warm water springs in what is now Big Bend National Park. Boquilla Spring and Spring 4 (Graham Ranch Springs) were definitely occupied; Spring 1 may have been as well [2]. The Boquilla Spring population was extirpated when flows ceased in 1954. Flows were later restored, but contamination with western mosquito fish (Gambusia affinis) continues to make Boquilla Spring uninhabitable. The Spring 4 population crashed between 1954 and 1956, as was extirpated by 1960 due to contamination by western mosquito fish and the diversion of flows to provide drinking water and a fishing pool for the Rio Grande Village Campground in 1954. Predation by the introduced green sunfish may have been a factor as well. Today the species occurs in three intensely managed, artificial spring areas within Big Bend National Park and in two captive populations (Dexter National Fish Hatchery and University of Texas at Austin).

During an unsuccessful 1956 effort to eradicate western mosquito fish from Spring 4, Big Bend gambusia were relocated to other waters within Big Bend National park and to the University of Texas [2]. The park relocations failed, but the three University of Texas fish (two males and one female) survived. In 1957 they were returned to an artificial refugia specifically constructed for them within the park. The population thrived until 1960 when it was contaminated with western mosquito fish. At that time, 15 fish were relocated to the University of Texas, and 20 were relocated to a newly constructed refugia near the Rio Grande Village Campground. The new refugium was supplied by water from Spring 1. In 1968, the refugium was found to be contaminated with green sunfish [5]. The population of 250 fish was removed, the refugia drained and restored, and about 100 fish were reintroduced [5]. In the winter of 1975, nearly all fish in the refugia died (probably due to excessively cold water). The population was augmented the following year with fish from the University of Texas. A drainage ditch was created in 1976 to better regulate water temperatures. In 1978, the species was introduced into the ditch where it continues to thrive today. The third existing population was created by the 1984 reintroduction of fish to the Spring 4 outflow and stenothermal spring waters 50 meters to the southwest [3]. These populations have thrived, reaching approximately 50,000 fish in 2005 [6].

Though Big Bend gambusia conservation effort date back to the 1950s, the Park's chief biologist credits the Endangered Species Act with prompting the successful, systematic efforts to conserve the species habitat [5]. Continuing threats include water contamination, sedimentation from flooding, reduction in spring flows and introduction of western mosquito fish and green sunfish via floods or humans. In 2005, Big Bend National Park proposed to eliminate some campsites from the Rio Grande Village Campground and to cease diversion of Spring 4 water to the campground [4].

The University of Texas at Austin has maintained a captive population since 1956. The Dexter National Fish Hatchery population was established in 1974. It initially suffered from cold water die-offs, but has since been stabilized by temperature regulation efforts [2]. The 2005 population was about 50,000 fish [6].

[1] USFWS. 2005. Big Bend gambusia (Gambusia gaigei). U.S. Fish and Wildlife Service website (http://ecos.fws.gov/docs/life_histories/E004.html) accessed September 5, 2005.
[2] USFWS. 1984. Big Bend gambusia (Gambusia gaigei) Recovery Plan. U.S Fish and Wildlife Service, Albuquerque, NM.
[3] Hubbs, C.L., G. Hoddenbach and C.M. Fleming. 1986. An enigmatic population of Gambusia gaigei. Southwestern Naturalist 31:121-123.
[4] Big Bend National Park. 2005. General Management Plan for Big Bend National Park, Brewster County Texas. U.S National Park Service.
[5] Wauer, R. 1997. For All Seasons, A Big Bend Journal. Austin (University of Texas Press).
[6] Clark Hubbs. 2005. Personal communication with Clark Hubbs, Professor emeritus, School of Environmental Science, University of Texas, September 7, 2005.

Banner photo © Phillip Colla