J. Great Lakes Res. 24(4):845-858 Internat. Assoc. Great Lakes Res., 1998 Changes in the Biodiversity of Freshwater Mussels in the Canadian Waters of the Lower Great Lakes Drainage Basin Over the Past 140 Years Janice L. Metcalfe-Smith1*, Shawn K. Staton2, Gerald L. Mackie3, and Nancy M. Lane4 1 Aquatic Ecosystem Protection Branch National Water Research Institute, P.O. Box 5050, 867 Lakeshore Road Burlington, Ontario L7R 4A6 2R.R. #1, Rosedene Road St. Ann's, Ontario LOR 1Y0 3Department of Zoology, University of Guelph Guelph, Ontario N1G 2W1 42099 Grand Ravine Drive Oakville, Ontario L6H 6B4 Abstract. Severe declines in the diversity and abundance of freshwater mussels have been documented over the past century in the United States. Although similar trends might be expected in Canada, mussels have received little attention to date. The Committee On the Status of Endangered Wildlife In Canada (COSEWIC) expanded its mandate in 1994 to include invertebrates, thus providing the impetus for assessing the health of Canada's fresh- water mussel fauna. The purpose of this study was to determine if there have been changes over time in the richness and composition of freshwater mussel communities in the lower Great Lakes drainage basin, which historically supported the most diverse and unique mussel fauna in Canada. Over 4,100 occurrence records for 40 species of mussels collected from approximately 1,500 sites between 1860 and 1996 were compiled and examined together for the first time. Comparisons of historical and recent data revealed a pattern of species losses and changing community composition throughout the basin, particularly in the species-rich Lake Erie and Lake St. Clair drainages. River systems that once supported numerous species characteristic of a wide variety of habitats are now dominated by fewer siltation- and pollu- tion-tolerant species of the Subfamily Anodontinae. A detailed examination of the data for the Grand, Thames, and Moira rivers confirmed that the same trends are occurring in widely- separated systems throughout the basin. The results of this study provide compelling eviden- ce that the steady decline in freshwater mussel diversity that has been documented for the United States is also occurring in Canada. INDEX WORDS: Freshwater mussels, Unionidae, biodiversity, Great Lakes, historical. *Corresponding author. Email: [email protected] Introduction Freshwater mussels are among the most endangered groups of animals in North America (Biggins et al. 1995). The decline of mussels was apparent by the turn of this century, and there is evidence that the process is accelerating at an alarming rate (Neves 1997). The con- struction of dams and creation of impoundments during the first part of the century destroyed riverine habitat for indigenous species and led to their genetic isolation. Water pollution and the relentless destruction of riparian buffer zones adjacent to watercourses are also im- plicated in the collapse of the mussel fauna. The introduction of the zebra mussel (Dreissena polymorpha) to the Great Lakes in the late 1980s (Hebert et al. 1989), and its eventual spre- ad to the major river systems of 19 states and two provinces (U.S. Geological Survey 1997) has led to catastrophic declines of native mussels in infested areas. Freshwater mussels have been protected under endangered species legislation in the United States since 1973 (Neves 1997). However, it wasn't until 1994 that the Committee On the Status of Endangered Wildlife In Canada (COSEWIC) expanded its mandate to include invertebrates. The Mollusc Working Group of the Lepidoptera and Mollusca Subcommittee of COSEWIC was formed in 1995 to develop a national list of Canadian mollusc species at risk and prepare status reports on them. Although Canada does not have federal endangered species legislation at this time, the provinces of Ontario, New Brunswick, Quebec and Manitoba have standalone Endangered Species Acts (Aniskowicz 1997) that protect endan- gered flora and fauna from willful destruction. The Committee On the Status of Species At Risk in Ontario (COSSARO) recently began to list aquatic species, including freshwater mu- ssels. The Natural Heritage Information Centre (NHIC), an affiliate of The Nature Conser- vancy, was formed in 1993 to compile, maintain, and provide data on rare, threatened, and endangered species and spaces in Ontario (NHIC 1994). The NHIC currently ranks 50% of Ontario's native mussel species as either very rare, extremely rare, or known only from histo- rical records. Now that the plight of mussels has been officially recognized by these organi- zations, it is timely to conduct a detailed assessment of the health of Canada's freshwater mussel fauna. The purpose of this study was to determine if there have been changes over time in the diver- sity and/or composition of freshwater mussel communities in the Canadian waters of the lower Great Lakes drainage basin. This area was chosen for study for two reasons. First, the region historically supported the most diverse and unique mussel fauna in Canada, with 40 of the 53 Canadian species occurring here. The Sydenham River, for example, is considered to be "... the richest system for Unionidae in Canada and one of the richest small river systems in North America" (Clarke 1992). Secondly, zebra mussels have virtually eliminated native mussels from Lake St. Clair (Nalepa et al. 1996), western Lake Erie (Schloesser and Nalepa 1994), and the upper St. Lawrence River (Ricciardi et al. 1996), leaving the rivers and stre- ams of the drainage basin as the last refuge for many species. This study relied upon historical occurrence records for mussel species, which were gathered over a 140-year period by nearly 200 different investigators, as its information base. As might be expected, the data were very inconsistent with respect to sampling method, samp- ling effort, and spatial and temporal coverage. In most cases, only the presence of a species was recorded; i.e., measures of abundance were rare. Furthermore, no details (other than sampling location) were available for a large portion of the earliest records. Historical data of this nature are extremely valuable, as they provide insights that are not obtainable any other way. However, they must be considered qualitative and cannot be subjected to statistical testing. In their overview of the use of historical information to direct aquatic habitat management in the Great Lakes, Steedman et al. (1996) cautioned that historical information is typically of low resolution, and should be used to "... specify only qualitative genera- lizations about past ecosystem states and processes." In the present study, generalizations are derived concerning the past and present health of the mussel fauna of the lower Great Lakes drainage basin from the available historical and recent data. Materials and Methods Study Area The study area consisted of the Canadian waters of the lower Great Lakes (Lake St. Clair, Lake Erie, and Lake Ontario), their connecting rivers, and all watersheds draining into the la- kes within the boundaries of the Province of Ontario (Fig. 1). The Lower Great Lakes Unionid Database All available historical and recent data on the occurrences of mussel species throughout the study area were compiled into a computerized GIS-linked database. Data sources included the primary literature, natural history museums, federal, provincial, and municipal govern- ment agencies (and some American agencies), conservation authorities, Remedial Action Plans for the Great Lakes Areas of Concern, university theses, and environmental consulting firms. Mussel collections held by six natural history museums in the Great Lakes region (Canadian Museum of Nature, Ohio State University Museum of Biological Diversity, Royal Ontario Museum, University of Michigan Museum of Zoology, Rochester Museum and Sci- ence Center, and Buffalo Museum of Science) were the primary sources of information, ac- counting for over two-thirds of the data acquired. The database was created using Microsoft® Access (Version 7.0), and linked by means of Spansmap® (Version 1.4) to 1:250,000 digital base maps of southwestern Ontario that were provided by the Geomatics Office of Environment Canada, Burlington, Ontario. The databa- se presently consists of over 4,100 unionid records obtained from approximately 1,500 sites between 1860 and 1996; a record is defined here as the occurrence of a given species at a given location on a given date. The database variables include data source, name of collector, collection date, name of waterway, description of sampling location, geographical coordina- tes, species, condition of specimens at time of collection (living or dead), and number of species collected from a given site. As very few of the data from any source had been geo- referenced, coordinates (latitude and longitude) were assigned to collection sites based on descriptions of site locations. Taxonomy was standardized to the nomenclature most recently adopted by the Freshwater Mussels Subcommittee of the American Fisheries Society Endan- gered Species Committee (Williams et al. 1993). Limitations of the Data As noted earlier, historical data such as these contain many inconsistencies. For example, the sampling methods used and effort expended by amateurs picking up a few shells for their collections, museum curators conducting extensive surveys, and Ph.D. students sampling intensively for their thesis research are sure to differ but were seldom documented. Further-