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Robert Hansen is a field biologist studying and
monitoring aquatic life at Barton Springs. He works for the City of
Austin's Drainage Utility Department, which is the agency in charge of
stormwater drainage. That agency also tracks how water gets channeled
back into the creeks, ponds and rivers in Austin.
A school of Mexican Tetras in Barton Springs.
This is one of three kinds of sunfish that live in Barton Springs.
On a rainy day in March, Robert Hansen suiting up for a dive and survey of the pool. The lone lifeguard on duty sits high in his chair, inscrutable, under a large square umbrella. Two people swim and a handful of people are standing around the side of the pool. A woman asks him about his scuba gear. They start talking about fish that live in the pool. She says, "I guess I've never seen any bass. I've seen the catfish..."
"We've got two species of bass and three species of sunfish," Hansen says with diligent precision.
"Really?" she says. She sounds surprised.
Hansen nods toward two cormorants near the diving board. "They're very opportunistic. They keep diving to the bottom, feeding on crayfish, and schools of [Mexican] tetras. There's plenty of food for them here in Barton Springs." What's life look like at 16 feet deep? "The school of tetras, which has several thousand fish in it, would just divide in half as a cormorant would swim through it and head to the bottom. And then they'd come right back together after the cormorant had passed through the school."
In the deeper parts of this underwater jungle we see large patches of Sagittaria, also called arrowhead grass for its leaf-shape. Sagittaria is common in lower Barton Creek and the part of the Colorado River Austinites know as Town Lake. "These patches started from 5 to 10 plants," Hansen says. About 10 percent of the pool floor is now covered--that's 9000 square feet. According to Hansen, these plants keeps the sediment in the pool down and balance excess nutrients in the water. "It provides wonderful habitat for the fish, for the crayfish. Several times I've been scuba diving over this patch where I could see a 2 or 3-foot catfish just laying down there. Fish and turtles are really attracted to it."
The Barton Springs Pool community includes 3 kinds of turtles, and 12 to 15 kinds of fish. Most of these animals spend their time eating, foraging, hiding and trying not to be eaten. Minnow-like Mexican tetras feed on insect larvae, snails and aquatic worms on the water's surface, they also love to eat organic material stirred up from the pool's sediment. Since tetras are small (about as long as two paperclips), they school together for safety. This makes it hard for cormorants, sunfish and bass to single one fish out. Sunfish and bass will eat almost anything smaller they are. Deeper down, on the pool floor, channel catfish lie in limestone cracks and casually browse for insects and snails in the vegetation. Catfish, which are most active at night, have no real enemies in the pool. Barton Springs' underwater parade also includes orange throat- and green throat darters, gray redhorses that look like carp (they are not), green sunfish, and long-ear sunfish (they have flaps on the sides of their heads which look like "ears"). Of the red-breasted sunfish, Hansen says "they're beautiful during mating season."
With all this eating and hiding, do fish sleep? "They rest," Hansen says. How? They find vegetation and cover, and kind of hover there. Right. Until something larger, hungry and nocturnal, like the freshwater eels, show up.
Then there are those animals that live in and out of the water: mallards and blue heron, turtles like the Texas cooter, the red-eared slider, and the occasional snapping turtle, which will eat anything--even ducks. Cormorants, those diving brown wonders that "fly" underwater, prey on salamanders and worms, and the crayfish that live in the grasses. Crayfish are filter feeders and eat organic debris and detritus that fall to the pool. This makes crayfish "detritivores." Also located near this end of the food chain are the salamanders, who eat animals that look like tiny shrimp, pillbugs, mayflies, and snails.
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