Boaters key to slowing invasive species
Last Tuesday, during National Invasive Species Awareness Week, a crew from Texas Parks and Wildlife Department’s aquatic habitat enhancement team spent the day on Lake Athens trying — successfully, they hope — to prevent the 1,500-acre reservoir and its thriving fishery from becoming the 22nd public reservoir in the state to suffer an infestation of giant salvinia.
If the unknown boater who loosed on Lake Athens the non-native aquatic plant that can cover a water body and smother the life from it had followed some of the basic tenets of responsible boating — or followed Texas law — the reservoir almost certainly would have been spared this latest threat.
Texas boaters hold the key to preventing or at least slowing the spread of some of the invasive aquatic species that threaten the state’s inland waters and the fisheries that depend upon them. Their boats and trailers serve as the primary method transporting many of these invasives to new sites.
“Just some simple actions — cleaning, draining, drying your boat and trailer — can make a big difference,” said John Findeisen, who leads the Brookelandbased TPWD aquatic habitat enhancement team that battles invasive vegetation in the waters of eastern Texas. “It can help prevent spread of invasives from already-affected lakes to new ones.” War knows no end
Texas lakes need that help. The state has seen a disturbing flurry of discoveries of new infestations by two of the most virulent aquatic invasives — giant salvinia and zebra mussels — over the last year. Seven lakes have been affected, with four new infestations discovered or confirmed in the last month.
Over the last year, six lakes — Murvaul, Fork, Palestine, Martin Creek, Nacogdoches and Athens — have been added to the list of reservoirs documented to be infested with giant salvinia. Discovery of the plant on Nacogdoches and Athens came during February.
Along with the nearly two dozen public reservoirs, dozens of private lakes and ponds have been found to be holding the floating plant native to South America. That spread has occurred over just 20 years; salvinia was first documented in Texas in 1998, when the plant, sold in the aquarium trade, was found in a small pond on the grounds of a Houston school.
Since then, the plant, free in an environment lacking natural controls present in its native range, has manifested its ability to reproduce and grow at an astounding rate. The floating plant can grow to carpet waterways, preventing sunlight from reaching native aquatic vegetation, stopping photosynthesis and stripping water of the dissolved oxygen crucial to fish and other aquatic life.
Like water hyacinth, another hugely problematic aquatic invasive plant with which it sometimes is found in concert, salvinia can create huge, dense mats that boats find almost impenetrable. These mats can cover thousands of acres. A mix of hyacinth and salvinia has covered almost half of 25,000-acre Caddo Lake. Last summer, a 5,000-acre patch of salvinia floated on Toledo Bend Reservoir, Findeisen said.
Once established, the aquatic invasive plants are almost impossible to eradicate. Efforts to control the plants using herbicides and biological controls such as weevils that eat only the target plant have limited success. And they are hideously expensive. The Texas Legislature this past year appropriated $6.3 million to TPWD to combat aquatic invasive species during the 2018-19 biennium. River and water authorities as well as the federal government also annually spend millions in the effort. Hope for Lake Athens
If discovered when infestations are small enough and in a confined area, salvinia sometimes can be removed or killed before it spreads. That is what Findeisen hopes the agency has been able to accomplish at Lake Athens.
The plants — less than an acre’s worth — were discovered around a boat ramp. Such locations commonly are the site where initial infestations are found, indicating the plants arrived on a boat or, more likely, a boat trailer. When boaters retrieve their vessels from infested lakes, plants or pieces of plants can cling to boats, motors or trailers; most often, plants will be caught between the boat’s hull and the trailer bunks.
When that boat is next launched, the plants float free.
All it takes is just a couple of plants or, in the case of salvinia, which spreads by simple vegetative reproduction, pieces of plants to start a new infestation.
Fast action that included placing floating booms around the Lake Athens site, careful application of herbicide and manual removal of plants may have been able to prevent salvinia from establishing itself on Lake Athens, Findeisen said.
“We hope we got it early enough,” he said.
There is no such hope of eradication or even modest control for Texas waters infested with zebra mussels. And the list of Texas lakes and river basins holding these small mollusks, native to Eurasia, has steadily grown since first found in Texas waters at Lake Texoma in 2009.
Since then, the mussels have spread from that single site on the Red River to 14 water bodies and four more river basins — Trinity, Brazos, Guadalupe and Colorado.
How did they get there? They were transported to new areas as adults that had attached to the hulls or outside of engines of recreational boats or as microscopic larvae — veligers — hiding in bilge, live wells or other water-holding areas of boats.
And when they get there, bad things happen to the lakes’ fishery and beyond.
A single zebra mussel produces about 1 million eggs a year. The population quickly grows to billions, with the mollusks covering any exposed hard surface. The resulting damage to water management transportation infrastructure such as pipes, pumps, intake screens and other machinery costs billions of dollars nationwide and hundreds of millions in Texas.
Fisheries and the rest of the aquatic ecosystem are at risk, too. Through sheer numbers, the mussels outcompete beneficial native clams and mollusks. They also change a lake’s water chemistry, stripping suspended minerals from the water as material for their shells. The mussels feed on microscopic plankton — the base of the food chain that supports forage species such as threadfin shad.
Once a lake is colonized, there is no way to eradicate or even attempt to manage the mollusks.
Last year, a half-dozen Texas lakes were added to the list of those documented with zebra mussels, with the invasives showing up for the first time in the Guadalupe River basin (Canyon Lake) and the Colorado River basin (lakes Travis and Austin).
Last month, TPWD’s aggressive statewide sampling program documented a reproducing population of zebra mussels in Lake Austin. The Lower Colorado River Authority found mussel larvae in samples from Lady Bird Lake just downstream from Lake Travis. 14 lakes on infested list
Fourteen lakes in five river basins are officially listed as “infested” with zebra mussels. Another five are listed as “positive” for the invasives, meaning zebra mussels have been detected on multiple samplings and another three are listed as “suspect.”
“When zebra mussels were found in the Colorado River Basin, we knew it was likely that larvae would disperse and invade downstream water bodies,” said Monica McGarrity, TPWD aquatic invasive species team leader. “But downstream dispersal doesn’t spread zebra mussels to new river basins — boats do — and boats can spread them downstream more quickly.
“Texans can protect other river basins and prevent zebra mussels from spreading more quickly to other reservoirs by being extremely diligent about cleaning, draining and drying their boats and other gear every time they visit any lake or river,” McGarrity said in the agency’s announcement of the latest discoveries.
That diligence is the responsible thing for boat owners to do. It’s also the law.
Texas law requires boat owners to remove and properly dispose of salvinia, water hyacinth and any other invasive aquatic vegetation from their boat or trailer; transporting the prohibited vegetation is punishable by a fine of as much as $500.
Transporting zebra mussels, dead or alive, also is prohibited. And boaters are required to drain all water from their boat, livewells, bilge and other onboard receptacles before leaving or approaching a body of freshwater to prevent zebra mussel adults or microscopic larvae from being transferred to non-infected waters. The drain/dry requirement applies to all boats of all sizes and propulsion used on public water. Violation of the drain/ dry regulation carries a fine of as much as $500.
“It doesn’t take that long to comply with the clean, drain, dry rules,” Findeisen said. “And it’s the best defense we have right now.”