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TPWD News,, 512-389-8030

Feb. 28, 2005

TPWD Voices Concern About Spread of Giant Salvinia

AUSTIN, Texas — The expansion of one of the world’s most noxious aquatic weeds — giant salvinia — on Toledo Bend and possible spread to Sam Rayburn represents a serious threat to two of the state’s largest reservoirs, according to Texas Parks and Wildlife Department fisheries biologists.

Biologists fear the plant will take over shallow coves where largemouth bass spawn and could therefore seriously impact the fishery. Giant salvinia forms thick floating mats that block sunlight and prevent the production of microscopic organisms vital to healthy fish populations. With good growing conditions, the plant can produce nearly 100 tons of biomass per acre, and once the floating mass dies and sinks, the decomposing material can use up all the oxygen in the water.

“One of our biggest problems is giant salvinia is transported easily,” said Howard Elder, a TPWD aquatic vegetation biologist. “The proximity and accessibility of these two reservoirs makes transportation a very real threat.”

That’s why department officials are urging boaters to take precautions to minimize unintentional spread of this noxious plant. Boaters should flush livewells and clean boats and trailers thoroughly after each trip to Toledo Bend to avoid carrying giant salvinia fragments.

“We are concerned that some anglers and boaters use both Toledo Bend and Sam Rayburn and trailer boats from one lake to the other,” Elder added. “If you do not remove giant salvinia from your boat or trailer before you leave the lake, you can be charged with possessing and transporting harmful exotic plants. These charges carry penalties of fines and/or jail time.”

First discovered in Texas in 1998, giant salvinia was probably sold for use in water gardens by nurseries that had no idea its importation or possession is prohibited by both the U.S. Department of Agriculture and TPWD. “One good flood empties out somebody’s backyard and infests the whole watershed,” said Elder. “Giant salvinia is easily transported over land to new locations by boat trailers, propellers and the intakes of personal watercraft. Considering the proximity and popularity of Toledo Bend and Sam Rayburn, its introduction to Sam Rayburn must be considered inevitable unless extreme measures are taken.”

TPWD and the Sabine River Authority have been battling the invasion with herbicides, but the rains of 2004 kept Toledo Bend Reservoir full and allowed the plant to spread into shallow, stump-filled areas where spraying boats can’t go. “In 2004, it overwhelmed us. We were able to treat only 228 acres,” Elder said. “Our goal is to keep it contained in Toledo Bend and keep it from reaching Sam Rayburn.”

This floating fern, a native of South America, can double in size weekly and if left unchecked can cover large areas in a relatively short time. In 2003, giant salvinia covered 124 acres on Toledo Bend; in 2004, it spread over 3,070 acres despite ongoing herbicide treatments by both Texas and Louisiana. Sam Rayburn Reservoir may be the next target.

“The mild winter allowed the spread to continue, and we can expect an increased expansion this year, which will warrant increased treatment,” Elder said. “We have ongoing chemical treatments on Toledo Bend; the problem is because the lake is so large we cannot get to it before it spreads.”

TPWD has begun large-scale introductions of a bio-control agent, the salvinia weevil Cyrtobagous salviniae, which feeds on the plants and may have long-term potential. It takes the weevils about two years to establish, and the department has deployed more than 300,000 statewide thus far.

“We are optimistic establishment will occur by spring of 2005, and will continue introductions through summer of 2005. The success of the salvinia weevil has been documented in several countries. I hope they do as well in Texas,” Elder said.

SL 2005-02-28

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