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Carp to be released to control hydrilla in Lee Hall and Diascund reservoirs

In an effort to encourage a healthy aquatic habitat, which fosters a healthy water supply, Newport News Waterworks will be releasing sterile grass carp into the Diascund and Lee Hall reservoirs on Monday, March 25.

Media Contact
2013 Mar 21

In an effort to encourage a healthy aquatic habitat, which fosters a healthy water supply, Newport News Waterworks will be releasing sterile grass carp into the Diascund and Lee Hall reservoirs on Monday, March 25. The carp are known plant eaters, and are expected to help control the invasive hydrilla plant, which is causing environmental concerns in Diascund Reservoir, while the Lee Hall Reservoir release will be part of a pilot project. The time of the release is not confirmed as yet.

Hydrilla verticillata, also known as waterweed, is a submerged freshwater plant that is native to Europe, Africa and Asia. It is thought to have been introduced to the United States by the Florida aquarium trade in the 1960’s and since that time, has spread throughout much of the southeast and Mid-Atlantic regions of the U.S. Hydrilla grows rapidly and forms dense mats that can crowd out native aquatic plants, harm fish populations and impede boat traffic. Once established, hydrilla can be very difficult to control.

In the Diascund Reservoir, patches of hydrilla were first noted by landowners and Waterworks staff in 2007. It has quickly spread and as of late summer 2011, dense hydrilla growth could be found in many areas of the reservoir.

As the hydrilla has grown, so have the number of complaints received from adjacent landowners, boaters and fishermen. Landowners complain that they cannot access the reservoir for recreational purposes during the warmer months of the year, and some believe that their property values may be affected. Boaters complain that the hydrilla mats make navigation in the reservoirs difficult and cause large portions of the reservoirs to be inaccessible for fishing, especially in shallower water. Hydrilla plants caught in the props of their electric trolling motors need to be frequently removed to prevent the batteries from overheating.

The Virginia Department of Game and Inland Fisheries (VDGIF) biologists who monitor the fish population in Diascund Reservoir are beginning to notice some unwelcomed changes due to the hydrilla growth. The dense mats provide places for small prey fish (blue gills, other sunfish) to hide from the larger predator fish (largemouth bass, etc.). When this happens the reservoir can become over-populated with prey fish and the over-population results in stunted, less healthy fish. Since the bluegill like to feed on largemouth bass eggs and young, an over-abundance of blue gill can lead to a decrease in the number of largemouth bass in the reservoir. In their 2012 electrofishing survey of Diascund Reservoir, the VDGIF noticed a significant increase in the number of small bluegill present.

Once hydrilla has become established, it is nearly impossible to remove it completely or permanently. Without some type of control, hydrilla could spread throughout most of reservoir. While there are numerous control options available, what seems to work best in other reservoirs around the state is the introduction of a hydrilla-eating fish called the white amur carp or grass carp.

These fish are native to eastern China and Siberia and are one of the largest members of the minnow family. They were first brought to the U.S. in the 1960’s to study their ability to help control unwanted aquatic plants. The carp were found to be effective plant eaters but there was concern that introducing a breeding population of non-native fish to U.S. lakes and rivers could cause problems. In the 1980’s however, biologists discovered a way to alter the carp eggs that would result in adult fish that were sterile and therefore unable to reproduce. Since then the carp have been stocked in lakes and ponds across the country to aid in controlling nuisance aquatic plants.

Waterworks will stock 1,000 of the sterile grass carp in Diascund Reservoir. One hundred will be released into the Lee Hall Reservoir, which has much less hydrilla than Diascund, as a pilot program. The carp, hatched and raised at a fish farm in Arkansas, will be 10 to 12 inches in size in order to prevent them from being quickly eaten by other fish. The U.S. Fish and Wildlife Service will test the fish to ensure they are sterile before they are brought into the state. Smith Minnow Farm in Victoria, Virginia, will deliver the fish to Newport News.

According to Andrew Rich, Waterworks’ Watershed Property Administrator, “Our goal is to keep the amount of hydrilla in the reservoir to an acceptable level, not to completely eradicate it. With the assistance of the Virginia Department of Game and Inland Fisheries, we will be monitoring the fish and their effect on the hydrilla for the next few years to find out if 1,000 fish are going to provide the level of control needed.”

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