The Dock Line
Lake Conroe, Texas (936) 890-7234
Safe Summer Fun on Lake Conroe
By Mark Webb
Based on the results of our (TPWD’s) March/April hydrilla survey the result we’ve been waiting on has come and hydrilla is on its way out of Lake Conroe. The latest survey shows a total of 363 acres of hydrilla down from 2,052 acres of hydrilla in January of 2008. The reason for the rapid decrease is approximately 109,000 triploid grass carp feeding in Lake Conroe. The addition of 33,000 grass carp early this spring brought the number of grass carp per acre of hydrilla to 55 overwhelming hydrilla growth and beginning a crash in the hydrilla population. As of April the reduction in hydrilla had led to a staggering ratio of over 300 grass carp per acre of hydrilla. By the time this article goes to press the hydrilla in Lake Conroe is probably almost completely gone. So where do we go from here? Even though it looks like we’ve won the current battle against hydrilla the war of habitat management at Lake Conroe continues.
The Future of Hydrilla
The characteristics of hydrilla that made it a problem in Lake Conroe to begin with make it a continuing threat. In addition to being easily spread by fragments, hydrilla produces starchy tubers buried in the soil. These tubers don’t all sprout at once but rather come up over a period of years helping to insure the hydrilla’s survival. At Lake Conroe that means that the grass carp will have about 2,000 acres of sprouting tubers to feed on for two years or more. TPWD will continue hydrilla surveys on a regular basis and if the hydrilla begins to outgrow the ability of the grass carp to control it the stocking of additional fish will be recommended. Keep in mind that although there are a lot of grass carp in Lake Conroe today, the number will decrease by about 32% per year due to natural mortality.
Native Aquatic Vegetation
Native aquatic vegetation has been an important component of the Lake Conroe ecosystem for many years. Even though there are numerous species of native vegetation in Lake Conroe the plants fall into three main growth forms: emergent, floating, and submersed.
Native emergent vegetation including cattail, bulrush, and pickerelweed grows in two feet of water or less with most of the plant above water. These plants provide good habitat for fish spawning and provide a home for insects that young fish feed on. They’re also excellent at reducing shoreline erosion. Fortunately many emergent species are already well established in Lake Conroe and are usually resistant to grass carp herbivory because of their thick, tough stems.
Native floating vegetation consists primarily of fragrant and yellow water lilies and American lotus. These species are good at providing shade and cover for fish and the insects they feed on and stabilizing the bottom against wave action. Again, floating species are fairly resistant to grass carp except when the young shoots are emerging in the spring.
Native submersed plants including the pondweeds, wild celery, coontail, and water star grass are probably the most valuable as habitat for fish and other wildlife. Because they grow almost completely underwater they provide oxygen to the water column, they stabilize the bottom and prevent erosion, they filter and clear the water, they provide a home and food for aquatic insects that fish and other wildlife feed on, and they provide excellent cover for juvenile fish, but because they grow underwater and because they tend to have small stems (since the water supports most of their weight) they are the most vulnerable to grass carp and other herbivores. It’s these plants that we’re the most concerned with going forward and because of these concerns TPWD, SJRA, Seven Coves Bass Club and others are continuing to establish native submersed vegetation along the shallow shoreline of the upper end of Lake Conroe.
Other Exotic Vegetation
Even though hydrilla appears to be under control that doesn’t mean we don’t have exotic vegetation concerns at Lake Conroe. Giant salvinia, water hyacinth, and water lettuce are all three exotic floating species capable of very rapid expansion leading to economic, recreational, and ecological damage to the lake. Although grass carp are not effective at controlling these species, there are biological control insects that can be used in an integrated pest management approach to bring these plants under control and keep them that way. To that end the Seven Coves Bass Club has started a nursery for giant salvinia weevils to assist in the control of this plant while all of these species are being aggressively treated with herbicide by SJRA with assistance from TPWD.
Thanks!
Control of hydrilla and other exotic vegetation on Lake Conroe is at times a difficult and very expensive task. It could not be accomplished without the cooperative effort of homeowners, anglers, boaters, other recreational users, business owners and government entities. On behalf of TPWD we would like to express our deepest thanks for the support and cooperation of all the Lake Conroe users in making successful management of this fantastic resource possible! If you have questions you can contact us at mark.webb@ tpwd.state.tx.us or earl.chilton@tpwd.state.tx.us or by calling (979) 822-5067 or (512) 389-4652
Email: ozzy@docklinemagazine.com or susan@docklinemagazine.com
The Dock Line - PO Box 1203 Willis, Texas 77378