Conservation

Glass Eels Found in Texas for the First Time

Scientists document early life stage of eels, solve mystery of eel movements.

After a yearlong concentrated monitoring project, scientists documented a glass eel in Texas waters for the first time in January of this year.

Glass eels are a life stage of the American eel (Anguilla rostrata). This species spawns in the Sargasso Sea, in the North Atlantic Ocean, and their larvae drift on ocean currents to the Atlantic or Gulf of Mexico coasts. There, they transform into a tiny, transparent stage known as glass eels and swim into estuaries and up rivers, eventually maturing into juveniles known as elvers and then into yellow eels. These live for many years in fresh or saltwater before developing reproductive organs and returning to the Sargasso Sea to start the life cycle all over.

Until now, only yellow eels had been seen in Texas, and only two glass eels ever in the entire Gulf of Mexico — one in Mexico and one in Florida.
“We knew they had to be here, though,” says Texas Parks and Wildlife Department aquatic biologist Stephen Curtis.

To find them, TPWD funded a monitoring project in partnership with the University of Houston–Clear Lake’s Environmental Institute of Houston. A team hand-built eel ramps — small boxes with a ramp that eels can swim up and a bucket to collect them.

“Building a box is a lot harder than you would think,” says Jenny Oakly, project manager at the university. “It took a few months to test the design and a while to build them.” The team tested the design and deployment of the ramps in different settings and officially deployed them at 12 sites in late June and early July 2022 along the coast from the Louisiana border to Port Lavaca and in the Colorado River.

The first glass eel showed up in January 2023. From then through March, the ramps caught more glass eels. “The glass eels were getting larger and more pigmented, and then we were collecting elvers,” Curtis says. “We saw this transition through time as juvenile eels came into our bays and estuaries.”

Officially, the University of Houston monitored eight sites, TPWD three, and the Lower Colorado River Authority one on the Colorado River, but those involved stress it took a team effort. They visited every site every week until summer 2023.

The finding helps answer the question of when glass eels move into Texas waters and in what numbers, Curtis says. Now the scientists can move on to other questions.

“We hope to look at more sites and to monitor those annually to see what the catch looks like, the numbers, the timing of when they come into our waters and that sort of thing,” says Jillian Swinford, a project manager with the TPWD Coastal Fisheries Division. “We have a smaller window to work with now, and we know that the ramps work.”

Oakly says scientists can start figuring out what affects the timing of eel movements. “Putting out these ramps and checking them more frequently could answer bigger questions,” Oakly says. “Such as what makes them come into our waters when they do. For example, is it the moon or tides or freshwater inflow influences? This study really focused just on when and where they arrive, so we hope to have some follow-up studies.”

Eels play an important role in the marine ecosystem, and knowing where these fish are makes it possible to protect them, Curtis says. Finding glass eels in Texas was an important step and, for the scientists, a just reward for a year of hard work.