Perhaps it is only fitting that in Texas, where everything is famously big, people battling an invasive aquatic plant should seek out an appropriately enormous solution: the grass carp, a plant-devouring fish that can reach 400 pounds. Said to be able to eat their weight in greenery every day, grass carp have been known to denude entire lakes of vegetation of every kind. Though they are strictly vegetarian, and do not eat other fish, they can destroy underwater flora that other fish species need.
So what? say many people who have had to live with the foreign plant, known as hydrilla, that is plaguing Texas.
A fast-growing tangle, hydrilla is clogging lakes and rivers, putting an end to days of boating and swimming, jamming water intakes and shutting down hydroelectric operations. In some places it has formed tangles so thick that it has been blamed in drownings.
When 1,600 grass carp were released into Lake Austin in February, homeowners and many water resource managers hailed the fish as the best hope for subduing hydrilla. But others fear the fish could become an even bigger environmental problem than the one that it was brought in to solve ˜ a situation that has become all too familiar to those releasing one foreign species to eradicate another.
If the fish destroy all the lake’s vegetation, critics say bass fishing and water quality will decline in this drinking-water reservoir and recreational lake formed by the damming of Texas’ Colorado River.
And if the fish escape from the lake, as many predict they will, they could make their way downriver to destroy sea grass beds in estuaries that are home to productive fisheries.
“The carp don’t just go away and die after they are done with the hydrilla,” said Dwayne Anderson, the Texas program director for Clean Water Action, an environmental group.“It’s another nonnative species with no predator, and it will be an eating machine, and it will be destructive.”
Ed Parten, president of a fishermen’s association created to fight the grass carp, described the fish as a scourge on the state’s tradition of bass fishing.“Wherever the carp has been used, the bass fishing has declined from fabulous to extremely poor,” he said, adding that fishing should be of wide interest because it brings the state billions of dollars each year.
But the fishermen have yet to sway homeowners around Lake Austin who miss the lakeside life they once enjoyed and who fear property values may fall as the plant clogs the waters. Also, many dismiss the economic importance of bass fishing.
“Maybe they bought a six pack of beer before they put the boat in,” said Shirley Coleman, who lives on the lake where the average home costs more than a million dollars. She is a member of Friends of Lake Austin, a group of lake users organized to eradicate the weed.“Hydrilla is wicked stuff,” she said.“While we’re sitting here arguing about it, hydrilla is taking over more and more of the lake.”
Hydrilla, originally native to Asia and Australia, is believed to have been introduced accidentally in Florida in the 1950’s, possibly when someone emptied a fish tank and set the aquarium plant free. Because hydrilla can resprout from the tiniest piece of a broken stem, the plant has traveled easily on motorboat propellers and boat trailers across the country to Arizona and California, costing many millions of dollars in eradication, control and water-system repairs. Hydrilla has shown up as far north as Washington State, and last year it turned up in Maine.
Hydrilla covered 23 acres of Lake Austin in 1999, but by last May it covered 300. Growing in long strands upward from its roots in the sediment and branching out profusely at the surface, the plant creates dense curtains and mats of vines, tangling boat propellers, tripping up wake boarders, snagging water-skiers and frightening off swimmers.
So far no method of control has satisfied everyone. There were vehement objections to the use of herbicides in this reservoir. Boats can mow and harvest hydrilla, a method preferred by fishermen and environmentalists, but many say the process is too expensive and inefficient.
Dams have been used to lower the level of water in the lake, exposing the hydrilla to killing cold in the winter. But the plants surge back in the spring. Managers have even explored using tiny enemies, like the hydrilla fly and a hydrilla beetle, though neither has proved terribly effective.
For many, the only answer is to buy grass carp that have been rendered safely sterile, and then release the hungry swimmers by the thousands, as is under way at Lake Austin.
“I work with foreign species problems so I have some qualms, but I’ve looked at this issue from all kinds of different angles,” said Dr. Tom Arsuffi, an aquatic ecologist at Southwest Texas State University, who recently completed a tracking study showing that even in a flood, small numbers of radio-tagged fish did not escape the dammed Lake Austin and swim downriver.“This is a long-term solution. With the right amount of fish, the grass carp can keep the hydrilla trimmed for 20 years.”
So far, the 1,600 grass carp released into Lake Austin have had no obvious effect. Texas Parks and Wildlife gave the city a permit to release as many as 6,400. Mary Gilroy, an environmental scientist with the city, said it would release the fish in increments as necessary.
But far from achieving a neat solution, scientists say Lake Austin’s ecological experiment has just begun.
For years, researchers have tried without success to find a method for determining how many grass carp are required for a given situation. Still shooting in the dark, managers can never be sure if they will get no effect, perfectly proportioned elimination or if the fish will eradicate every bit of greenery.
Critics also fear there is a danger that fertile fish could end up in the water. Companies that sell grass carp typically subject fertilized eggs to intense pressure, causing the egg to retain an extra set of chromosomes and rendering it sterile.
Dr. Earl Chilton, aquatic habitat enhancement program director at Texas Parks and Wildlife, said that every fish was tested once. Any fertile fish, that is, any fish carrying the normal number of chromosomes, are removed. A second small sample is tested later and if any fish are fertile, the entire batch is tossed out, Dr. Chilton said.
But despite safeguards, critics say it is still possible for a fertile fish to be released and establish a permanent population of these crafty creatures that are so difficult to catch, even in a net.
So far, all the heat around grass carp seems to center around Lake Austin. Yet it is in the Rio Grande, where another major release of grass carp was approved by the state last month, that hydrilla has arguably done its most awesome damage.
With the river already low because of a drought, hydrilla has clogged its channel, slowing water flow and encouraging quicker evaporation. As a result, the mighty Rio Grande, an international waterway and an international border, has turned into a drying dribble, just yards short of the ocean.
In fact, because the United States-Mexico border is in the river, the control of hydrilla is considerably more complex than in Lake Austin. Cutter boats must avoid crossing the border. Herbicides have been out of the question because scientists were unable to find an appropriate chemical approved for use in both countries.
Yet despite the fact that 23,000 grass carp will soon be released in the Rio Grande, Dr. Chilton said only two people showed up for a public meeting on the situation. He noted that the Mexican government was in favor of using the fish and that the Fish and Wildlife Service had sent written notice that it expected no bad effects from the carp.
Twenty years ago though, nearly 300,000 fertile grass carp were released in Lake Conroe, Tex.
“Lake Conroe went from being a world-class bass fishery to a big mudhole,” said Mr. Anderson, describing the lake as an unmitigated disaster, stripped of vegetation, foreign and native.
But not everyone agrees.
“It’s so strange,” said Ms. Coleman, who found the negative reaction quizzical.“The Lake Conroe people successfully conquered it. They say it’s beautiful.”