Presenter: Howard Elder

Commission Agenda Item No. 10
Briefing
Exotic Aquatic Vegetation on Toledo Bend Reservoir
January 2005

I. Executive Summary: Two of the State's foremost fisheries, Toledo Bend and Sam Rayburn Reservoir, are currently under severe threat from the expansion of giant salvinia (Salvinia molesta), an extremely invasive aquatic fern from South America. Giant salvinia is currently on the "Harmful or Potentially Harmful Exotic Fish, Shellfish, and Aquatic Plants" list. Once established, the floating exotic can form dense mats that eliminate all other aquatic vegetation in the area, eliminating even phytoplankton and zooplankton which are vital to fish populations. Giant salvinia can exhibit phenomenal growth rates and is easily spread overland to new locations by boat trailers, propellers, and the intakes of personal watercraft. Mild winter temperatures and high water levels in the spring and summer of 2004 have resulted in the expansion of giant salvinia throughout Toledo Bend Reservoir. Its introduction to Sam Rayburn Reservoir must be considered inevitable, considering the proximity of the two reservoirs.

II. Discussion: First discovered on Toledo Bend Reservoir in 1998, isolated infestations of giant salvinia were held in check for two years by aggressive herbicide treatments conducted by TPWD and the Louisiana Department of Wildlife and Fisheries. An extended drawdown of the reservoir by the Sabine River Authority in 2000 helped to further suppress expansion of giant salvinia, stranding many plants on dry land. More recent control efforts have focused on continued herbicide treatments and the large-scale introduction of a bio-control agent in the form of the giant salvinia weevil (Cyrtobagous salviniae). Although it may take as long as two years for reproducing populations of weevils to establish, it is hoped results of these on-going introductions may be apparent as soon as spring 2005.

III. Recommendation: Staff recommends the Texas Parks and Wildlife Commission adopt the following motion:

The Texas Parks and Wildlife Commission adopts amendments to §59.10, §§69.5, 69.8, §§69.19-69.21, §§69.24-69.27, §69.71, §69.77, §69.301 and §69.303. The Texas Parks and Wildlife Commission also adopts the completed rule review of Chapters 59 and 69.


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