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Using grass carpAs the temperatures begin to warm, it seems that pond owners have become concerned about aquatic vegetation and fish. As mentioned in an article written by Mike Porter from the Noble Foundation, aquatic vegetation problems may not always be a problem. For most ponds it is very desirable to have some aquatic vegetation present in your pond. Aquatic vegetation helps maintain clearer water, provides a habitat for fish, and minimizes bank erosion. Most ponds in our area are used for sport fishing and livestock and therefore function best with moderate amounts of aquatic vegetation. But too much of a good thing can be a problem. When it comes time to control aquatic vegetation, it can be challenging at times but there are methods that do work effectively. The most important thing to remember when you begin to control aquatic vegetation is proper identification of the plant you are wanting to control. Controlling aquatic vegetation with grass carp is one of the options available to pond owners with aquatic plant problems. In many situations, the use of grass carp is an economical, long lasting, and effective option. However, grass carp are not appropriate for every pond with abundant aquatic plants. Whether grass carp should be stocked in a pond or not, depends on the goals for the pond, the plant species causing problems, and the probability of grass carp escaping the pond. Grass carp should not be stocked in a pond where attracting ducks is an important goal for the pond. Most ducks, especially surface-feeding (dabbling) ducks such as mallards, eat aquatic plants and are attracted to ponds with aquatic plants. Grass carp prefer many of the plant species that attract ducks. Grass carp generally should not be stocked into a pond or wetland where maintaining a natural ecosystem is an important goal. Aquatic plants are a natural component of shallow ponds and wetlands. Grass carp are not native--they are introduced from eastern Asia. Aquatic plants are important components of habitat for many native animals. When clear water is an important goal of North Central Texas ponds, grass carp probably should not be stocked. Ponds with aquatic plants generally have clearer water than ponds without aquatic plants. Aquatic plants stabilize a pond's bottom and banks, which help prevent the pond from becoming muddy when wind or animals stir the water. Aquatic plants help flocculate suspended soil particles, maintaining clearer water by settling soil particles to the bottom or onto plants. Grass carp recycle the nutrients trapped in aquatic plants back into the water. When grass carp are stocked at rates high enough to control aquatic plants, the recycled nutrients often stimulate a phytoplankton bloom that generally reduces water clarity. In a pond where largemouth bass-bream sport fishing is an important goal, it is desirable for aquatic plants to dominate 5-25 percent of the pond. Grass carp are probably not a good choice for a bass-bream sport fishing pond where plants cover less than 25 percent of the pond. Grass carp maintain control for a long period of time. Plant control can be maintained for up to 20 years. Grass carp should be at least 8 inches long when stocked to avoid predation. Grass carp are usually stocked at rates ranging from 5 to 10 per acre. The 10 per acre stocking rate generally removes all submersed aquatic plants and most immersed aquatic plants within two years. A pond manager in these situations generally prefers no submersed or immersed aquatic plants. Stocked at appropriate rates, grass carp control most species of submersed aquatic plants and many species of immersed aquatic plants. Grass carp sometimes control large coarse stemmed aquatic plants such as cattail, bulrush, and American lotus, but in other situations they do not. Some immersed plants, such as water willow, are rarely or never controlled by grass carp. Grass carp should never be stocked into a pond where there is a substantial risk of escape. Grass carp live in rivers in their natural environment so they actively search for moving water. They can escape through an unprotected spillway with as little as 3 inches of water flow. Grass carp can not reproduce in ponds but they can reproduce in some rivers. Grass carp can damage or destroy native wildlife and fish habitats by removing aquatic plants and indirectly causing increased water. For this reason, it is against the law to release grass carp into public waters in Texas. If grass carp escape, the investment in aquatic vegetation control washes downstream with the grass carp. Grass carp should be stocked only in a pond with properly designed fish barriers on the spillways or in a pond with no overflow. If water will flow through both an overflow pipe and an emergency spillway, both need barriers. Once you have determined that releasing grass carp would be an option, you must apply for a permit. Applications can be obtained by calling the Dept. of Wildlife. Often, types of aquatic vegetation include mechanical removal and chemical control. This can also be very effective but more expensive than utilizing grass carp. Some situations may warrant the use of chemical control in order to decrease the time it takes to control the weeds. Date: 7/5/07
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