First Veligers Found in Lake Michigan Water Intakes

From July 26, 1991 (update #9)

Zebra mussel veligers were found in Lake Michigan water intakes for the first time in late June and early July -- proof that the mollusk is actively reproducing in the lake. Veligers were first found on June 27 in a water intake sample collected in southern Lake Michigan at the Northern Indiana Public Service Company (NIPSCO) Bailly Generating Station in Gary, Ind., according to Ellen Marsden, assistant scientist with the Illinois Natural History Survey. The sample contained a relatively low density of 22.7 veligers per gallon (6 per L). Even lower densities (about four per gallon, less than one per liter) were found on the same day in samples from LTV Steel and another NIPSCO plant at Hammond, Ind. These veliger densities are much lower than densities currently found in Lakes Erie and Ontario. Samples taken from some of the same locations on July 11 showed similar concentrations of veligers, although the Bailly Station was not resampled due to a plant shutdown. Veligers at even lower densities (0.3 per gallon/0.09 per L) were found by Jory Jonas, assistant coordinator for the Wisconsin Zebra Mussel Watch, in plankton water samples taken July 8 by Muskegon, Mich., water filtration plant personnel. In another sample taken July 14, Jonas found veligers at densities of 0.2 per gallon (0.05 per L) in samples from the same locagion. On July 9, personnel at the B.C. Cobb power plant on Muskegon Lake found an estimated 420 recently settle zebra mussels per square foot (5,382 per square meter) on concrete blocks they had placed in the water to detect zebra mussels. Settled zebra mussels were also found July 16 on substrate samplers placed in Muskegon Lake by Michigan Sea Grant Extension Agent Charles Pistis. The fiberglass plates that Pistis had placed in the water to detect zebra mussels were found to contain 27 mussels ranging in size from 0.098 to 0.157 inches (2.5-4 mm).

ID: 19910726-2.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.