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Big Bend's Namesake Fish Saved from Extinction
by Meagan Racey
Photo Credit: USFWS
The Boquillas Crossing Spring went dry in 1954.
As the water disappeared, so too did the various fish and wildlife species that depended on it. One of just two existing populations of the Big Bend gambusia (Gambusia gaigei) was lost when the spring went dry.
The remaining population of this tiny, silver fish persisted in another spring in Texas' Big Bend National Park—in the Rio Grande Village in extreme southwestern Texas. This spring was soon diverted for a fishing pool, however, where non-native green sunfish (Lepomis cyanellus) preyed on the minnow-like gambusia, and survivors faced insurmountable competition from the western mosquitofish (Gambusia affinis).
Between the two populations, just three fish survived. These individuals were removed from the wild and safeguarded at the University of Texas at Austin. All surviving Big Bend gambusias have descended from these three fish.
With a precariously low population, the gambusia's chances for survival were grim and extinction seemed inevitable. The species was listed as federally endangered under the Endangered Species Preservation Act in 1967—the first piece of comprehensive endangered species legislation. It was among the first species to gain federal protection.
This small fish has fought for its survival.
Today, the species can only be found in two small, man-made ponds within the Big Bend National Park—the smallest geographic range of any known vertebrate. To survive, these fish need a clear, shallow home fed by warm springs teaming with insects like mosquito larvae for food. Though Big Bend gambusia thrived for centuries in this habitat along the Rio Grande, its existence is now threatened by waning spring flows, fluctuating water temperatures, and competition with other fish.
Photo Credit: USFWS
A diverse team of partners is working to ensuring the species' future, including biologists from the U.S. Fish and Wildlife Service's Austin Ecological Services Field Office and its Southwestern Native Aquatic Resources and Recovery Center (formerly Dexter National Fish Hatchery and Technology Center), the National Park Service, the University of Texas at Austin, the University of Texas-Pan American, and the Texas Parks and Wildlife Department.
The UT-Austin's research aquarium has raised thousands of offspring from the three survivors and provided them to Big Bend National Park, where staff carefully maintains the manmade ponds in the Rio Grande Village.
With such a small range, the species is extremely vulnerable to random events like flooding and disease outbreak—catastrophic events that could eliminate the species. The team has managed to save the Big Bend gambusia a number of times from various narrow escapes, including cold-water spells and predation by non-native fish. In 2008, the team rescued hundreds of gambusia during extremely high river flows from the flooding originating from the Rio Conchos in Mexico. Biologists transported close to 700 fish to the Southwestern Native Aquatic Resources and Recovery Center, where they were safe from the varying water levels and temperatures.
A captive stock remains at the Southwestern Native Aquatic Resources and Recovery Center to help ensure future gambusia generations. As the recovery team plans ahead for the Big Bend gambusia, it has concerns for the long-term viability of a population built off of just three fish. However, results from the pond and hatchery stocks show enough genetic diversity to give biologists hope for the species.
Why the large effort for such a tiny fish? The conservation team's response is one full of pride for being part of a nation where the weakest and the voiceless get the opportunity to persevere.
Meagan Racey, a public affairs specialist in the Service's Northeast Regional Office, can be reached at firstname.lastname@example.org or 413-253-8558.
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