ZEBRA MUSSEL DISTRIBUTION UPDATE

JULY 1997

The descriptions below give the range and represent the most significant new information of zebra mussel sightings in the major hydrologic units of the United States.

UPPER MISSISSIPPI:

According to researchers with the USGS in Wisconsin, zebra mussel densities continue to increase at Lock and Dams on the upper Mississippi River. Settlement occurred in July near La Crosse, Wisconsin and adult populations are said to be "very dense" there. Concern over native mussel populations is still warranted as many were covered with zebra mussels. In a major tributary of the Mississippi, several zebra mussels were found in the St. Croix River near its confluence with the Mississippi River late in the summer of 1996. Because of this, boaters are being encouraged not to take their boats from infested waters to the St. Croix because of the endangered populations of native mussels inhabiting the river. Despite this effort, approximately 40 juveniles were found last month on a plate sampler by the National Park Service above the site of the endangered mussel bed. In the Illinois River, the number of adults was low, but veliger numbers were up relative to last year.

LOWER MISSISSIPPI:

The U.S. Fish and Wildlife reported no new locations of zebra mussels this year. However, zebra mussels can still be found in the lower Mississippi River and also in the Atchafalaya River basin. The annual cycle of warm summer temperatures in the river appears to be too high for successful reproduction and long-term survival. Recruitment probably comes from reproduction upriver or reintroduction by barges.

ARKANSAS-WHITE-RED:

A record spawning event took place in Lake Dardanelle on the Arkansas River this Spring according to one biologist at Arkansas Tech University. In May, the settling rate of juveniles was 2.6 million/m². This translated to over 77, 000/m² adults in mid-July. By the end of July, populations at various sampling sites suffered large die-offs of 80-100% as water temperatures approached 32^oC. Impacts on the fisheries so far are minimal. Water clarity has increased giving way to the growth of rooted submergent macrophytes not normally present.

OHIO:

The U.S. Fish and Wildlife Service found a 10-30 fold increase late in 1996 over the previous year in the densities of zebra mussels in the Ohio River. Although they have not begun this Summer's monitoring, preliminary observations have not revealed any recruitment so far for 1997. In the upper Ohio Valley of Pennsylvania, the Corps of Engineers reported new locations for zebra mussels. The first occurrance in the Ohio River (Mile 13.3) was at Dashields Lock and Dam, just west of Pittsburgh. Several adults were collected from the lock chamber during a routine inspection in February of this year. Two months later, adults were collected from Lock 3 on the Monongahela River (Mile 23.8) near Elizabeth, Pennsylvania. Last summer, a small number of adults were collected from Lock 4 on the Monongahela River (Mile 41.5) near Monesson, Pennsylvania. In the lower Ohio Valley, no zebra mussels have been found in the Cumberland River above Nashville.

MID-ATLANTIC:

Monitoring by the Vermont Department of Environmental Conservation showed that in 1996, adult zebra mussels in Lake Champlain expanded their range and dramatically increased production. Peak veligers densities have increased each year since they were discovered in 1993 reaching nearly 100,000/m³ in the southern part of the lake and over 10,000/m³ in the northern portion where the most recent colonization has taken place. Zebra mussels can be found throughout the lake, even in the northeastern arm where they had not been previously reported. DEC also noted that many native mussels at one monitoring site were recently dead and had 100-200 zebra mussels attached. In western New York, zebra mussels were observed in Saratoga Lake and for the first time (veligers only) in Lake George in 1996. In the Hudson River, south of Lake Champlain, biologists at the Institute for Ecological Studies in New York found the 1996 year class to be largest yet just as they had predicted. Zebra mussels can be found anywhere in the freshwater portion of the river. Densities so far this year are around 40,000/m² in the Hudson River.

GREAT LAKES:

Lakes Erie and Ontario continue to be hit hard by zebra mussels. Layers several inches thick are coating the bottoms, even areas of soft substrate according to USGS biologists. Survival of the remaining native mussels are still a big concern in those lakes. In states adjacent to the Great Lakes, zebra mussels have continued to expand their range into many small lakes. As of this summer the number of lakes where zebra mussels have been reported in Michigan is 45, followed by Indiana and New York each with 15, Ohio has 8, and Wiscon sin has 7. Zebra mussel veliger or adult observations have been reported from a total of 90 lakes in the 8 states bordering the Great Lakes, up from 79 a year ago. In May of this year, a newspaper in Escanaba, Michigan reported a paper company having to remove 400 cubic yards of zebra mussels from its intake in Lake Michigan at a cost of 1.4 million dollars. Lake Superior still maintains low level populations.

TENNESSEE:

According to TVA biologists, zebra mussel densities are again up slightly from last year in the Tennessee River. Reproduction is still evident at all the power plants on the river. There also appears to be plenty of veligers at the upper end of the river. Settlement was not evident until July near Chickamauga Dam. Large mussels were observed at Watts Bar where the density had doubled from last year to 60/m². Densities in the lower portion of the river remain low at 7/m² at River Mile 100.5. However, last year the density was only 2.2/m² at that same site. Above Kentucky Dam at River Mile 23.4, the density was 45/m² this year. Biologists believe that the population has yet to reach its peak in the Tennessee River.

CALIFORNIA:

The California Department of Water Resources reported three more boats brought into the state since June of 1996 carried zebra mussels. Headed for saltwater destinations, all three boats came from the Great Lakes region and had been dry-docked long enough to kill the attached zebra mussels. The first of these three boats was stopped at the Hornbrook Inspection Station near the Oregon border in June of last year. The other two boats were stopped at the Truckee Inspection Station near the Nevada border in September and December of 1996. This brings the total to eleven boats since 1993.

For further information:

Currently, a World Wide Web server http://nas.er.usgs.gov is available to anyone with access to Internet. The web server provides real-time, spatial and logical queries of our nonindigenous aquatic species data sets. This is by no means all the information on confirmed zebra mussel sightings but feel we have received accurate information through a network of contacts to sufficiently represent the distribution. We welcome your input with information about new sightings.

For further information contact:

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U.S. Department of the Interior | U.S. Geological Survey URL: http://nas.er.usgs.gov Page Contact Information: Amy Benson - NAS Program Page Last Modified: June 20 2005