Chest-deep in the Cibolo Creek, aquatic biologist Zoe Nichols tried to electrocute a fish.
“This is a backpack electrofisher,” she explained, pointing at a ghostbuster-esque box. “Basically it just gently stuns the fish so we can catch them.”
“It kind of draws them out from cover or from whatever habitat we’re seeking them from,” said Chris Vaughn, senior aquatic biologist for the San Antonio River Authority. “Today, we are just doing a quick survey. We’re specifically looking for flathead catfish and longnose gar or spotted gar.”
The researchers catch, count and release those species. Flathead catfish, longnose gar and spotted gar are known as “host fish” for freshwater mussels, which researchers are trying to return to the upper San Antonio River. To get the mussels back, they have to figure out if there are enough host fish.
“These baby mussels clamp on to the fish gills,” Nichols said. “They infest the fish, and then it goes through this parasitic life cycle where they stay on the fish and they transform. It takes about a couple weeks. And then once the fish can either swim upstream or downstream, the mussels will drop off, and then they kind of repeat that life cycle. So that’s why it’s really important that we get these fish because the mussels can’t reproduce without it.”
Mussel beds enhance underwater habitats, making it easier for other aquatic species to thrive.
Freshwater mussels still inhabit the lower reaches of the San Antonio River, but habitat degradation and declining water quality and quantity have forced them to all but disappear from the upper portion of the river.
“Throughout the last decade, we’ve really just kind of messed up the upper San Antonio River to the point where freshwater mussels just couldn’t hang on,” Vaughn said. “And we want them back because they provide so many ecosystem services that we don’t currently have. They’re a niche that we’d like to fill. It’s a much more intact system if we can have this full repertoire of native species.”
There’s one problem: on this cold morning, the backpack electrofisher malfunctioned. Without the ability to attract and gently stun fish, the researchers struggled to get the count started. But, Vaughn said, other outings have been more successful, and researchers are optimistic about the prospects of a freshwater mussel comeback in the upper San Antonio River.