Caddo Lake’s Giant Salvinia problems are a warning for other lakes

Published 2:57 pm Sunday, July 3, 2016

CADDO LAKE – It doesn’t take long on the water to recognize two things about Caddo Lake. This has got to be the signature site in East Texas. Nothing, not even the Big Thicket, can compare to the beauty and unique character of this lake.

Known for its cypress trees, Spanish moss, odd characters, and at times odd sites along with good fishing, the lake is a gem.

The second thing that has to be noticed, is that sadly and by pure accident, giant salvinia has in some ways created an environmental disaster on the lake that at times cuts off access to portions of the lake. Maybe more importantly, it will most likely never be eliminated.

The slow-rolling shaded waters on the Texas side of the border lake with Louisiana are an ideal nursery for the South American invasive vegetation to grow. And even with a multi-pronged attempt to eliminate it, the best Texas Parks and Wildlife Department and its counterparts in Louisiana can hope to do is contain it because the same habitat it grows so well makes efforts to eradicate it near impossible.

Giant salvinia is a South American plant that most likely found its way into North America as a plant for backyard ponds or fish tanks. Like so many other things of this type that eventually becomes a problem it was dumped into public waterways.

The plant first was first found on a lake in South Carolina in 1996. Two years later it had made its way into Texas. Today it is found in 12 states, mostly in the warmer climates, including Hawaii.

“Caddo Lake has had giant salvinia since 2006. That was the first time it was introduced at a boat ramp on the Louisiana side, and then in 2007 we had a separate introduction on the Texas side of the lake,” said Tim Bister, Texas Parks and Wildlife Department Fisheries district biologist from Marshall.

At its worst on Caddo it has socked in more than 6,000 acres of the Texas side at a time, creating a mat of vegetation that can only be maneuvered by use of an airport. Following the drought of 2011 TPWD biologists estimated coverage was down to 600 acres, but for a plant that can double in mass every five to 10 days, it did not take long for coverage to spread.

Giant salvinia is one of a number of invasive species the TPWD is dealing with in the state. Salvinia is a major concern because it can completely block boating traffic and making areas of lakes unfishable.

It is currently found on 13 Texas lakes. It had been located on seven others, but was quickly treated and eradicated. There are two, Lake Fork and Falcon Reservoir, where it was discovered within the past year and biologists are hoping it was completely eradicated, but only time will tell.

“Giant salvinia really has no benefit to the environment, to fishing. It forms thick mats when it grows real thick. Sunlight can’t penetrate through it and it results in low oxygen in the water. Fish can’t use the water, native plants can’t grow underneath it, so it doesn’t do any good at all to have it here at the lake,” Bister noted.

Last week crews were attacking the salvinia on Caddo on two fronts. Spray crews contracted by the state were spraying chemicals in one area while the department’s Aquatic Habitat Enhancement team were releasing two boatloads of salvinia weevils.

“When you have an invasive species like giant salvinia it actually takes several approaches to manage it the best we can. We use herbicide applications and we are growing giant salvinia weevils which are native to Brazil. They actually feed on the plant and they lay eggs on the plant and the larva that hatch are going to eat the plants from the inside out. Our hope is that they are going to help control them,” Bister explained.

After limping along for years with a budget woefully short for taking on salvinia, zebra mussels, silver carp, lionfish and a host of other invasive aquatic species, the Texas Legislature kicked the current biennium funding up $1.1 million to $6.6 million. That has allowed for more spraying at lakes like Toledo Bend, Sam Rayburn, Texana, B.A. Steinhagen, Conroe, Sheldon, Livingston and others. In all about 3,000 acres of salvinia may be sprayed on Caddo this growing season.

The extra funding also is allowing the department to ramp up the weevil project, which has proven to be extremely successful in lakes in South Texas where winter cold is not an issue, and as far north as Steinhagen.

“The only thing they eat is giant salvinia and that is it,” said Shawn Malone, a TPWD Fisheries technician involved in the release. “It is just another tool in the tool box for us to use.

“They are not going to eat themselves out of house and home, but are just another way to help us control it.”

Malone said the weevils can get about 90 percent control in an area over time if there are enough of them. Studies have shown it takes about 700,000 of the miniscule weevils per acre to have an impact. And it can take a three-year timeframe. Therein lies the problem.

TPWD currently has two weevil nurseries operating and hopes to start a third at Caddo Lake. They are raised on giant salvinia and dumped into the lake where thick mats exist. The adults only live weeks, but their offspring and future generations continue the attack by expanding their range, moving from plant to plant and mat to mat.

At Caddo, creating a large enough population to have a sizeable impact has been difficult because the weevils cannot survive the cold winters at the lake like they can as little as 75 miles south at Steinhagen.

“Wintertime will knock back the weevils. It will hurt the giant salvinia, but it will come back faster than the weevils can, so then it takes off and outgrows what the weevils can take care of.

“Then by the fall the weevil numbers are ramping back up, and then we go back into winter and it knocks them back down,” Malone said.

At Caddo, boaters may see small amounts of salvinia floating in boat lanes down the lake or in massive mats under trees and in still backwaters. Those treating it often find themselves working the same area time and again as the wind switches directions and pushes mats back and forth, or pieces of the fern that were not killed expand.

“Coming back, it can (be depressing),” Malone said of working the same areas repetitively. “Especially if you think you have got it under control and are ahead of it and come back a month later and it doesn’t even look like you have been there.”

Fortunately enough of the lake remains open, so tourists can enjoy the beauty of Caddo Lake. Fishing has also not declined. But there are property owners who have not been able to move their boats in quite some time, and without a constant effort more of the lake could be socked in.

And even then, without even more tools chances are salvinia will be around forever.

“Caddo Lake is a complex place with all the cypress trees and all the cypress breaks. There is a lot of places for giant salvinia to grow that we can’t get to with herbicide spray equipment. That is one of the reasons salvinia weevils may be able to get to some of these places and help control it. There are so many areas where it can’t be controlled so there is always going to be giant salvinia at the lake,” Bister said.

And for that reason fishermen and boaters need to do their due diligence to make sure they are not trailering it from one lake to another.

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