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Eastern Pondmussel

Status: Endangered

Last examined by COSEWIC:April 2007


The Eastern Pondmussel is a medium-sized freshwater mussel with an elongated-oval-shaped and laterally compressed shell. The outside of the shell varies in colour from yellowish-black or greenish-black in juveniles and dark brown or black in adults. Narrow green rays, mostly at the posterior end of the shell, are often visible in juveniles and light-coloured adults. The average length of the adult shell is 70 mm.

The Eastern Pondmussel is a long-term brooder. Adults spawn in late summer and females brood the young from egg to larval stage in their gills over the winter months. In spring the mature larvae are released into the water and when they encounter a suitable fish host will attach themselves onto the gills of the fish. The larvae then are encased in the gills and proceed to undergo a period of development into juveniles. Juveniles eventually drop off the fish host and grow to adulthood in habitats that are sheltered, with slow-moving water, and fine sand and mud bottom. Adults and juveniles have similar diets which consist of organic debris, algae and bacteria gathered from the water column and/or sediments.

Where are they found?

In the delta area of Lake St. Clair and in a small tributary of the Upper St. Lawrence, Lyn Creek, near the outlet of Lake Ontario.

How many mussels are there?

In Lake St. Clair, studies indicate that the Eastern Pondmussel is widely distributed throughout the delta but in small numbers. The population is estimated to be 22,000 – 44,000 individuals. There is no population estimate for those mussels occurring in Lyn Creek.

Threats to the population

The introduction and spread of non-native mussels particularly the zebra mussel is the most significant threat to the existence of the Eastern Pondmussel in Lake St. Clair. Any changes to water levels in the lake as a result of climate change, for example, could negatively impact the species. Threats to the population of Lyn Creek have not been assessed.

COSEWIC Reason for Designation:

This was one of the most common species of freshwater mussel in the lower Great Lakes prior to the invasion of the zebra mussel (Dreissena polymorpha) in the late 1980s. Zebra mussels attach to the shells of native freshwater mussels in the hundreds or even thousands, causing the native mussels to suffocate and die from lack of food. Over 90% of historical records for the species are in waters that are now infested with zebra mussels and therefore uninhabitable. The species has declined dramatically and now occurs as two small, widely separated populations, one in the delta area of Lake St. Clair and one in a tributary of the upper St. Lawrence River. There is evidence that declines may be continuing at one location. Although zebra mussels appear to be declining in some areas, their impacts on this species may be irreversible if insufficient breeding adults have survived. Climate change is likely to cause a drop in water levels in the delta and further reduce the amount of habitat available to the mussel. Recent surveys in Lake St. Clair, which were conducted as a collaborative effort between Environment Canada and the Walpole Island First Nation, resulted in the identification of a significant refuge for this species within First Nation territory. The refuge is being managed by the First Nation for the protection of this and other aquatic Species at Risk with which it co-occurs.

What will happen if this mussel is added to the SARA List?

A recovery strategy must be prepared within one year of the Eastern Pondmussel being added to the SARA List.