Saving Canada's Endangered Mussels

Freshwater mussels are among the most endangered organisms in North America. Over the past century, researchers in the United States have reported severe declines in mussel diversity and abundance, but little was known about their status in Canada until recently. Now, a clear picture of what is happening to mussels in the lower Great Lakes drainage basin is beginning to emerge, and work is in progress to protect them.

North America has the greatest diversity of freshwater mussels in the world, with nearly 300 species. These invertebrates are particularly vulnerable to the effects of human activities because of a unique feature of their life cycle. Once their young have reached the larval stage, female mussels expel them into the water where they must attach to the gills or fins of a host fish to complete their development. This puts mussels at risk not only from environmental disturbances that affect them directly, such as habitat destruction, sedimentation and pollution, but also from those that affect their host fish.

The introduction of the zebra mussel to the Great Lakes in recent years has led to catastrophic consequences in an area that once boasted the most diverse and unique mussel fauna in Canada. Zebra mussels attach to the shells of native mussels, thereby interfering with their feeding, respiration, and burrowing. Populations of native mussels in Lake St. Clair, western Lake Erie, and the upper St. Lawrence River have been devastated.

Identifying and measuring mussels on the shores of the Thames River in southwestern Ontario.

In 1994, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) included invertebrates in its mandate for the first time, with molluscs one of the first two groups to be considered. This set the stage for researchers at Environment Canada's National Water Research Institute (NWRI) to launch a major effort to investigate the changes that have occurred in the composition of freshwater mussel communities in the lower Great Lakes drainage basin over the past century, and to identify species at risk.

Researchers gathered over 4 000 records taken between 1860 and 1996 on 40 species at 1 500 sites and entered them into a computerized database. The records came from a variety of sources, but primarily from six natural history museums in the Great Lakes area. Among the 200 investigators whose work was brought together for the first time were museum curators, graduate students, research scientists and 19th-century amateur naturalists.

When they analyzed the data, researchers discovered a pattern of species loss and changes in community composition throughout the basin, with displacement of many unique and ecologically fragile species by fewer pollution-tolerant species. The results of their work provided compelling evidence that the steady decline in mussel diversity already documented in the United States was also happening in Canada.

Researchers embarked on a risk-factor analysis to identify the species most at risk and to prepare a list of candidate species to be considered by COSEWIC for national status designation. A series of field studies conducted in various rivers in the research area in 1997-98 showed that the situation might not be as grim as originally thought. In the Grand River, which runs through Kitchener to Lake Erie, mussel populations appear to have rebounded, perhaps due to improvements in water quality resulting from better sewage treatment. The Sydenham River, in the southwesternmost tip of Ontario, was discovered to have the most diverse and intact mussel community of any of the rivers investigated, and probably of any in Canada, and is a major refuge for many rare species.

In 1999, based on NWRI's status reports and recommendations, COSEWIC designated three mussel species as endangered. Now, with funding from several sources, work is in progress to develop recovery plans to protect and restore mussel communities in the Great Lakes basin. Once the disturbances threatening the health of mussel communities have been identified and resolved, species can be restored by stocking with lab-reared specimens, augmenting small populations with specimens from larger populations, and reintroducing mussels back into their restored historic habitat.

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