Fish that lived only in San Marcos River now extinct
A tiny fish that lived only in the San Marcos River has now been officially declared extinct.
The U.S. Fish and Wildlife Service proposed removing the San Marcos gambusia from the endangered species list in 2021, saying all available data indicated it had been extinct in the wild for more than 35 years.
That rule was finalized Monday and takes effect in November. The fish species was listed as endangered in 1980, and the last time the gambusia was found in the wild was 1983.
The San Marcos gambusia grew up to about 1 inch long and had a prominent dark stripe along its dorsal fin, according to Texas Parks and Wildlife. It was one of the rarest species in the genus Gambusia, which live primarily in freshwater habitats and are found in North America, Central America and South America. The San Marcos gambusia ate small invertebrates, and unlike many other fish species, it gave birth to live young instead of laying eggs.
The San Marcos gambusia historically was found only in a small section of the river, between Rio Vista Dam and just downstream of Thompson’s Island, according to the U.S. Fish and Wildlife Service. The fish was listed as endangered due to its declining population and possibility of threats to its environment, including lower water levels, pollution and cutting of vegetation. Groundwater depletion, reduced spring flows, contamination, habitat impacts from severe drought and “cumulative effects of human activities” were all identified as threats to the species in 1978.
Reduced water flow from springs and “water pollution from the growth of nearby cities” were major threats to the species, as well as introduction of non-native species, according to Texas Parks and Wildlife.
Efforts to find the fish since 1983 were all unsuccessful, the U.S. Fish and Wildlife Service said, and none have been found since, despite “intensive searches.” Attempts at captive breeding were also unsuccessful, the agency said, in part because they couldn’t be found to be brought into captivity. The last captive female San Marcos gambusia died in 1985.
“All available information and field survey data support a determination that the San Marcos gambusia has been extinct in the wild for more than 35 years,” the rule says.
Other species removed from the endangered list this week for the same reason include several types of birds and mussels.
The San Marcos River is still home to seven species of endangered animals and plants: the Comal Springs dryopid beetle, Peck’s cave amphipod, fountain darter, San Marcos salamander, Comal Springs riffle bittle, Texas blind salamander and Texas wild rice, a type of underwater grass.