Forget for a moment the argument about the qualities of hydrilla and think instead about the mysteries of the aquatic vegetation.
There are years it can reduce access on a reservoir by a third or more, and then the next year it is gone only to show back up in full force a year or two later.
“I am sure there is a complex mix of environmental factors, but the short answer is we don’t have an answer. We do know it happens without treatment,” said Craig Bonds, Texas Parks and Wildlife Department regional fisheries biologist.
This is one of those years that the plant hasn’t made a nuisance of itself on a lowered lake Tyler, but is flourishing on Lake Fork.
“We know fluctuating water levels impact it, but we don’t know how. Sometimes lower water levels make it grow more and sometimes it will make it go away,” Bonds said.
He said there are examples where a lake will come up and then drop, and while the lake is down hydrilla will expand into areas it hasn’t been in several years.
“It will go like gangbusters for three or four years, and then it goes away,” Bonds said. “It is only speculation, but it might use up the nutrients available and then dies back.”
Lake Tyler is a good example of how finicky the plant can be. It exploded during the drought in 2006-07, but hasn’t this time around. Lake Tyler East hasn’t been sprayed since 2011.
There is no doubt that fishermen like hydrilla, but that view can often be considered by default because it might be the only vegetation on a lake and there is nothing to compare it to.
Bonds said TPWD biologists understand that sentiment and actually agree, up to a point.
“It is hard to paint a broad stroke across (the state) about how we feel,” Bonds said. “It is an evasive, non-native plant so we can’t spread it, but our perspective on how we treat it is not the same from lake to lake, but on a single lake basis. We can’t deny the fact that in the absence of native plants, in moderate communities it does provide decent habitat for sunfish and bass.”
The biological criteria for whether hydrilla is beneficial or not depends on how much of a lake if covers. Up to 30 percent is an accepted level. At 30 and up biologists have found it can limit predator fishes’ ability to catch prey fish, resulting in an unhealthy population. When the plant covers 60 percent or more of a lake’s surface that can lead to summer fish kills because of a lack of oxygen.
The real problem with hydrilla is normally on lakes like Lake Tyler where there are multiple user groups on the water. Skiers, lake-front homeowners, swimmers and pleasure boaters see nothing good in the floating vegetation that found its way into the U.S. in the 1960s as an aquarium plant.
That situation has put TPWD in an awkward position at some lakes where the managing authority opts to treat the vegetation with chemicals or grass carp against the fishermen’s wishes. Although it doesn’t actually treat the vegetation, TPWD is required to approve all treatments and has little recourse to impact a request other than to suggest options.
On other lakes without the user conflicts where spraying permits are not requested, little is done other than watching the plant come and go from year to year.
“We really have to take it on a lake by lake basis,” Bonds said. “On Toledo Bend, Fork and Amistad, lakes without conflicts, we survey it each year and don’t recommend treatment. We just monitor it.”
While Texas has learned to live with hydrilla, giant salvinia is a greater concern. The floating fern exists on 19 eastern Texas lakes, but has been found and removed from nine others. Chances are it won’t be removed on those where it has become established.
“We are much more concerned about the spread of giant salvinia,” Bonds said. “Under any situation it does not cover any fish habitat.”
The South American plant is believed to have gotten establish in Texas in the Houston area. It was probably brought in as a plant for backyard ponds.
What scares biologists is that giant salvinia can double in size weekly, making it impossible for spraying crews to keep up with in large infestations.
Bonds said Caddo and the northern reaches of Toledo Bend are two of the worst spots for salvinia. It is so bad at TB that some ramps are closed because boaters can’t get through it.
TPWD continues to do a public service campaign to tell boaters they are the ones that will spread the plant. Bonds said most have gotten the message, especially with the threat of a $500 fine hanging over them, but there are some who don’t care.
“The problem is there is a part of the boating public that is apathetic. They are knowingly transporting it from lake to lake, but for whatever reason they didn’t clean their boat,” Bonds said, adding citations have been written.
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