Shared from the 10/12/2021 San Antonio Express eEdition

Loss of a fish affirms fears about growth

Courtesy Texas Parks and Wildlife Department

The San Marcos gambusia was found only in a small section of the San Marcos River. The fish, about an inch in length, has been declared extinct after not having been seen for decades.

A tiny, rare fish found only in a small section of the San Marcos River has gone the way of the dodo.

The extinction of the San Marcos gambusia affirms the fears of scientists and environmentalists that mounting development and rapid population growth in Hays County threaten the survival of endangered species as well as the region’s water supply.

As it removed the river native from the endangered species list last month, the U.S. Fish and Wildlife Service said human activities contributed to the pollution and groundwater depletion that weakened the habitat and likely did the little fish in.

The San Marcos gambusia lived exclusively in the headwaters of the San Marcos River, according to the Texas Parks and Wildlife Department.

The fish, about 1 inch in length and with a dark stripe along the upper edges of its dorsal fin, hadn’t been spotted in the wild since 1982. The last captive one died in 1985.

Since then, extensive efforts by scientists and biologists to locate another San Marcos gambusia have proved futile.

Tim Bonner, a biology professor at Texas State University, has been studying all the fish in the San Marcos River for 25 years. He said the San Marcos gambusia’s genetics were never mapped fully because of a lack of technology at the time.

“It was first (discovered) in 1969, which is a relatively new discovery — most of our species in Texas were discovered back in the late 1800s,” he said. “So we’re talking a 13-year time period from when it was discovered” to when it disappeared in the wild.

“That’s just crazy to think about,” he said.

The San Marcos gambusia and 22 other species left the endangered species list this year because of extinction. Others include the ivory-billed woodpecker, a rare bird that lived in bottomland forests throughout the Southeast. The Little Mariana fruit bat was a small bat that lived primarily in Guam. And the Bach-man’s warbler was one of the smallest known warbler birds; it lived mostly in the Southeast during warm months and in Cuba during the cold.

The Fish and Wildlife Service pointed to loss of habitat and breeding grounds in many of the newly extinct species’ reports. Major maladies included lowered water tables, pollution, vegetation cutting, groundwater depletion, reduced spring flows and severe drought.

Also endangered

It’s human activity that most worries people like Dianne Wassenich, a river activist who led the San Marcos River Foundation for more than 30 years.

Several endangered species still call the river home, including fish such as the fountain darter, amphibians such as the Texas blind salamander and the San Marcos salamander, and native plants such as Texas wild rice. Wassenich said the growth of San Marcos and the surrounding region could seal the fate of those species like it did the San Marcos gambusia’s.

The extinct fish’s habitat took its share of punishment over the years.

Before the 1960s, people dredged the river with a backhoe to clear out the wild rice, Wassenich said.

“They got all the vegetation out. They wanted it to look like a concrete swimming pool,” she said. “That’s the habitat the fish lived in, so you can imagine how there have been a lot of changes over the thousands of years that fish may have lived there.”

The river even was rerouted to make room for Sewell Park, either during or before the 1960s, destabilizing the river dwellers’ home, Wassenich said.

“Water changes as you build around a spring and a recharge zone,” she said. “The character of the water changes so slightly — it could be a different acidity, temperature or some different component from road runoff.”

Fight for survival

Recent efforts such as the Edwards Aquifer Habitat Conservation Plan have made strides in attempting to conserve what little habitat the river’s endangered species have left.

Plan stakeholders have planted more wild rice in the San Marcos River, implemented programs that pay local farmers not to pump from the aquifer during periods of drought, and begun storing water in underground aquifer facilities to help keep it flowing when springs get low.

Additionally, places such as Texas State’s Meadows Center for Water and the Environment have several of the endangered species in captivity. That means they can be reintroduced to the river in case their numbers start to decline.

The human-based efforts, along with the natural high-velocity flow of the river, hearten scientists such as Bonner, the biology professor at Texas State.

Bonner said the flow of the river typically hovers between 150 and 170 cubic feet per second, which is strong for a river. The San Antonio River, by comparison, flows between 30 and 90 cubic feet per second.

The strong, spring-fed flow helps safeguard the river against the impact of overdevelopment.

“The flow allows it to resist a lot of changes and a lot of threats, like waste, pollution and fertilizer surface runoff,” Bonner said. “Once that stuff hits the San Marcos River, with this much velocity and flow, it wipes it out.”

But the river can’t protect itself against all effects of urbanization.

“If we dry up the springs, pump too much water out of the aquifer, then we no longer have the river acting like a river,” he said. “There are a lot of threats and a lot of ways we can still mess up the San Marcos River — and many of those threats are very real.”

Because of the San Marcos gambusia’s relatively short time in scientists’ logbooks, it’s hard to pinpoint what humans can do to spare other species its fate, Bonner said.

“I struggle to think about what the big lesson is,” he said.

For Wassenich, though, the lesson is simple: The endangered species that live in the San Marcos River need to be protected. Development along the river should be managed carefully to avoid mass disruptions in the region’s ecology.

“When you build on top of an aquifer recharge zone, as San Antonio has done,” she said, “you affect every living thing that depends on that aquifer and those springs.”

Annie Blanks writes for the Express-News through

Report for America, a national service program that places journalists in local newsrooms. annie.blanks

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