TX: 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 http://www.texasinvasives.org/ 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
http://www.tpwd.state.tx.us/newsmedia/releases/?req=20120126b.

 

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