DEEP-WATER POPULATION-STRUCTURE AND REPRODUCTIVE STATE OF QUAGGA MUSSELS (DREISSENA-BUGENSIS) IN LAKE-ERIE

Quagga mussel (Dreissena bugensis) population structure and reproducti ve status were assessed at deepwater (37 and 55 m) sites in eastern La ke Erie during July 1996. Mussels occupied similar to 70% of soft subs trates at 37-m sites and between 63 and 90% at 55-m sites. Shell lengt h and dry mass frequency distributions were similar at both sites, alt hough recruits less than or equal to 5 mm comprised a larger proportio n of the population at the deeper site. The population surveyed here a llocated disproportionately less mass to shell and more to soft tissue s relative to zebra mussels (Dreissena polymorpha) from shallow-water sites in eastern Lake Erie and from Lake St. Clair. The population at 55 m was slightly skewed toward male mussels (58%). Female mussels tha t were examined for reproductive state contained mature oocytes (80%) or had spent gonads (20%). Because water temperature at the site was o nly 4.8 degrees C, this survey provides the first evidence of gonadal development and spawning by quagga mussels at low temperature. These f indings contrast with most reports of spawning by congeneric zebra mus sels at temperatures greater than or equal to 12 degrees C but are con sistent with distributions of the species in different basins of the l ake.