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Species at Risk: The Northern Riffleshell

True or false? Freshwater mussels are among the most endangered species in North America.


As Canadians, we’re lucky to have such a large share of the world’s freshwater resources. When you consider the endangered status of freshwater mussels in Ontario, it’s scary to know that these mussels are actually indicators of overall ecosystem health. What does this say about the state of freshwater in Canada?

The northern riffleshell, a type of freshwater mussel, is listed as endangered under the federal Species at Risk Act. Its Canadian distribution is limited to the silt-free, highly oxygenated riffle habitat in Ontario’s Sydenham and Ausable Rivers. These two populations alone are critical to the global survival of the species, as they’re two of only four remaining populations in North America that show signs of recruitment.

The northern riffleshell, like most freshwater mussels, is experiencing population declines because of the presence of zebra mussels and deteriorating water quality. Zebra mussels are an invasive species that attach to the shells of mussels like the northern riffleshell and deprive them of basic resources by interfering with feeding, respiration, and burrowing. Since the introduction of zebra mussels into the Great Lakes in the late 1980s, they’ve devastated the native mussel communities in Ontario, including the northern riffleshell, which has lost over 95% of its historical range over the past century. Even worse than that: any loss of habitat by the invasion of zebra mussels is considered permanent.

Although zebra mussels have not yet reached the Sydenham and Ausable Rivers, poor water quality due to agricultural activities is also a threat to the northern riffleshell. The drainage of sediments and pollution into waterways from agricultural lands can clog the gills of the mussels, inhibiting their ability to feed and obtain oxygen.

However, hope has not been lost for this small mussel. Northern riffleshells were presumed extirpated from Canada until populations in the Sydenham and Ausable Rivers were found in 1997 and 1998. The rediscovery of these populations underlines the importance of recovery actions for species at risk in Canada. With the help of the federal Species at Risk Act, further commitments to research, monitoring, and stewardship activities have been included in the Recovery Strategy (2006) for the northern riffleshell. The best part? Any efforts to improve the conditions for this species will also help many other aquatic species as well!

Want to help ensure a healthy home for threatened species like the northern riffleshell mussel? Sign on now to support a strong federal Species at Risk Act! Help us send the message that a strong SARA is important to all Canadians.

Photo: Ausable Bayfield Conservation