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TPWD News,, 512-389-8030

Jan. 30, 2012

Zebra Mussel Test Results on North Texas Lakes Reported

Boaters urged to continue to Clean, Drain and Dry boats moved between lakes

ATHENS—Despite recent test results showing zebra mussel DNA to be present in several North Texas reservoirs, Texas Parks and Wildlife Department (TPWD) and U.S. Fish and Wildlife Service (USFWS) officials remain hopeful that the invasive aquatic species is still confined to Lake Texoma.

Dr. Robert McMahon, Professor Emeritus of Biology at the University of Texas at Arlington, has been monitoring 14 North Texas reservoirs for the presence of zebra mussels using three techniques. One technique looks for zebra mussel DNA in the water, another uses a microscope to look for zebra mussel larvae (veligers) in the water, and the third uses a submerged monitor to look for newly settled juvenile mussels.

Lakes involved in the study include Eagle Mountain, Lewisville, Lavon, Ray Hubbard, Ray Roberts, Arrowhead, Bridgeport, Tawakoni, Caddo, Wright Patman, Fork, Lake O’ the Pines, Caddo and Texoma.

Of those lakes, only Lake Texoma is known to be infested with zebra mussels.

Despite rigorous and repeated sampling in North Texas, Dr. McMahon has detected no zebra mussels of any life stage in any Texas lake other than Lake Texoma. Nevertheless, the most recent tests, carried out in October 2011, showed low levels of zebra mussel DNA in six lakes: Eagle Mountain, Lewisville, Ray Roberts, Arrowhead, Bridgeport and Caddo.

“Lakes Lavon, Ray Hubbard, Tawakoni and Wright Patman had no detected zebra mussel DNA in the samples,” said McMahon. “Lavon and Ray Hubbard tested positive for zebra mussel DNA in the spring of 2011, so the absence of any veliger DNA in the fall samples suggests that mussels have not become established in those lakes. Lakes Fork, Lake O’ the Pines and Bob Sandlin were not examined for mussel DNA in the fall of 2011, because they were considered inhospitable to zebra mussels based on high summer temperatures and low calcium levels.”

The presence of zebra mussel DNA in the water is not an indication that zebra mussels have become established in a lake or that they will become established. “There are cases in the western U.S. where positive DNA results indicated the presence of zebra mussels, but those results could never be confirmed,” said Brian Van Zee, TPWD Inland Fisheries regional director. “In fact, Lakes Ray Hubbard and Lavon tested positive in the spring of 2011 for zebra mussel DNA, but the presence of zebra mussels could not be confirmed by microscopy or settlement samplers. The spring 2011 samples were taken right around the time that contaminated boats were found on both lakes, so that may be why they tested positive. Both boats were removed and decontaminated, and subsequent monitoring on these two lakes, by three different entities, has not confirmed the presence of zebra mussels.”

McMahon noted that he was surprised by the positive result for Caddo Lake. “I consider the lake’s calcium levels to be too low and the summer water temperatures too high to support zebra mussels,” he said.

Microscopic examination of water samples from the 14 lakes in both June and October 2011 showed zebra mussel veligers present only in Lake Texoma. “During June juvenile mussels were found on settlement monitors only in Lake Texoma, while no juvenile zebra mussels were found on settlement monitors in any of the 14 lakes in October, including Texoma,” McMahon added.

McMahon suspects that boats being transported from Lake Texoma to other lakes are the source of the DNA found in the six lakes. “The data suggest that mussels and/or mussel larvae are being carried into these lakes by recreational boaters but are not becoming established as a sustainably reproducing mussel population,” he said. “This is a sign that mussels are being introduced to Texas lakes, and if such introductions continue, some of these lakes may eventually become infested with zebra mussels.”

“TPWD will continue monitoring these lakes for the presence of zebra mussels and doing everything it can to encourage boaters and anglers to Clean, Drain and Dry their boats for at least a week before moving them to another lake,” Van Zee said. “We encourage boaters and anglers to visit to learn more about how they can help protect the waters they enjoy.”

Concern over the possible transport of zebra mussels between bodies of water prompted TPWD to propose new regulations governing movement of boats or fish between lakes in North Texas. Details on the proposed regulations can be found at


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