ZEBRA MUSSEL DISTRIBUTION UPDATE

JULY 1996

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 National Biological Service in Wisconsin, zebra mussel densities continue to increase at lock and dams on the upper Mississippi River. Densities at the uppermost dams remain relatively low. Densities range from 1/m² at Lock and Dam 1 in St. Paul, Minnesota, to 11,432/m² at Lock and Dam 13 in Fulton, Illinois. Most of the Lock and Dams had densities greater than 1,000/m². The researchers say these numbers are up from last year. A successful recruitment during the summer of 1995 in the Illinois River had all but disappeared by the fall of 1995. Biologists at the Illinois Natural History Survey believe that only under flood events is the water in the Illinois River suitable for zebra mussel recruitment and survival. They reported that several recruitment events since 1993 corresponded with elevated water levels.

LOWER MISSISSIPPI:

Researchers at Louisiana State University, along with power companies, collected information on veliger densities in the lower Mississippi River this past winter. Densities range from no veligers at one of the upriver plants, to about 12/liter at a site in New Orleans. A total of seven plants along the Mississippi River reported finding veligers in January 1996. It has been suggested that the warm summer temperatures in the river are too high for successful reproduction and long-term survival. Recruitment probably comes from reproduction upriver or reintroduction by barges.

ARKANSAS-WHITE-RED:

Biologists with the Arkansas Game and Fish Commission confirmed the presence of zebra mussels again this year in the Arkansas River which continues to provide fertile waters for zebra mussel reproduction. Densities of zebra mussels are still increasing throughout the river in Arkansas and have now been found in the White River as far up as Clarendon, Arkansas.

OHIO:

Zebra mussels continue to spread in the upper reaches of the Ohio River drainage. In July 1995, several m ussels were reported from Chautauqua Lake in southwestern New York by the New York Dept. of Environmental Conservation. The Corps of Engineers continue to find mussels at previously uninfested facilities such as Maxwell Lock and Dam on the Monongahela River in southwestern Pennsylvania. In June of this year, several mussels were collected at Lock 4 on the Monongahela River. This was not surprising due to the presence of zebra mussels previously reported above and below Lock 4. Mid-way down the Ohio River drainage is the Kentucky River where the Kentucky River Authority reported finding zebra mussels in Pools 1 through 6 during August 1995. Additionally, a large monitoring effort began in 1995 to study the effects zebra mussels may have on native mussels in the Ohio River. Monitoring took place at native mussel beds where densities of zebra mussels ranged from about 4/m² at an upriver site to 3,540/m² at a downriver site. The Corps of Engineers reported low recruitment in the lower Ohio River late in 1995. Still, no zebra mussels have been found in the Cumberland River upriver from Nashville while densities in the lower portion of the river are slightly higher this year.

MID-ATLANTIC:

Monitoring by the Vermont Dept. of Environmental Conservation showed that adult zebra mussels densities in Lake Champlain were equal to or slightly higher than last year. However, veliger densities increased dramatically in northern parts of the lake and were found for the first time in the northeast arm. South of Lake Champlain, in the Hudson River, a strong 1992 year class of zebra mussels still dominates according to biologists at the Institute for Ecological Studies in New York. Biomass of these zebra mussels, however, is at its lowest since 1992. Biologists expect trends in biomass to be cyclical and predict an increase this year or the next.

GREAT LAKES:

In the Great Lakes region, zebra mussels have expanded their range to many small interior lakes of several states. Zebra mussel veliger or adult observations have now been reported from a total of 79 lakes in the 8 states bordering the Great Lakes. The number of Michigan lakes with zebra mussels occurrences increased from 29 to 41 lakes over the past 12 months. When zebra mussels first appeared on the scene, they were not expected to colonize the soft substrate which makes up much of the bottom of the Great Lakes. Researchers have since discovered zebra mussels colonize and persist on these soft substrates as well as submerged vegetation.

TENNESSEE:

According to Tennessee Valley Authority biologists, zebra mussel densities are up slightly from last year in the Tennessee River. Reproduction is still evident at all power plants and biologists believe that the population has yet to peak in the Tennessee River.

CALIFORNIA:

The California Department of Water Resources reported two more zebra mussel fouled boats entering into the state this year. This brings the total to eight boats since 1993. The first of these two boats was stopped at the Truckee Inspection Station in February. It was determined that the boat had come from Lake Michigan and that the zebra mussels found on the boat were dead. The second boat was stopped at the Yermo Inspection Station in April. It also had come from Lake Michigan but with a small number of live zebra mussels still attached to the propeller shaft. The boat was cleaned with a high pressure washer before allowing to proceed.

For further information:

Currently, a World Wide Web server http://nas.er.usgs.gov with this document and other zebra mussel information is available to anyone with access to Internet. The web server provides real-time, spatial and logical queries of our data sets. This is by no means all the information on confirmed zebra mussel sightings but we 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