Science Advisory Report  2012/082

Science advice from the risk assessment of three dreissenid mussels (Dreissena polymorpha, Dreissena rostriformis bugensis, and Mytilopsis leucophaeata) in Canadian freshwater ecosystems

Summary

• Zebra Mussel (Dreissena polymorpha) and Quagga Mussel (Dreissena rostriformis bugensis) pose a high risk to most regions of western Canada (Prairie region and BC) and the Laurentian Great Lakes. The assessment did not include the Maritime, Newfoundland/Labrador or Arctic regions of Canada.
• Risk of Dark Falsemussel (Mytilopsis leucophaeata) for freshwater ecosystems in Canada has been assessed as low. However, assessment of risk for brackish/estuarine systems is beyond the scope of this document and should be captured in a separate risk assessment.
• The probability of survival (habitat suitability) was determined primarily based on calcium concentrations which indicated that most watersheds in the prairies and Laurentian Great Lakes regions were highly suitable for survival and establishment of Zebra Mussel and Quagga Mussel.
• The probability of survival (habitat suitability) for Quebec and central/northwest Ontario (on the Canadian Shield) was determined to be low, as habitat is not suitable for Zebra Mussel or Quagga Mussel based on very low calcium levels.
• Probability of arrival was assessed using a Human Footprint Index and proximity to invaded habitats.
• This risk assessment was conducted at the spatial scale of Canadian sub-drainages and not for individual waterbodies. Thus, risk may differ at smaller spatial scales where conditions could be more (or less) favourable. Other considerations could include cottage traffic to some watersheds and differences between large lakes and large river systems within sub-drainages.
• Impacts of Zebra Mussel and Quagga Mussel establishment have been shown to have significant, irreversible ecological impacts to freshwater ecosystems. Though not included in this assessment, ecological impacts also have socioeconomic implications and have been well documented in Canada and elsewhere.
• Human-mediated dispersal, specifically recreational boating activities including overland transport of boat trailers and water-based equipment, are important vectors contributing to the spread of Zebra Mussel and Quagga Mussel in Canadian freshwaters.
• Natural dispersal downstream in major river systems can occur rapidly over large distances.
• Due to the well documented impacts associated with Zebra Mussel and Quagga Mussel invasions, the uncertainty of this risk assessment is very low. Uncertainties exist in data limitation associated with human-mediated dispersal of dreissenid mussels in Canada.
• An effort should be made to consolidate geo-referenced water quality data at the national level, which would improve future risk assessments.

This Science Advisory Report is from the March 27-28, 2012 National risk assessment of Zebra Mussel, Quagga Mussel and Dark Falsemussel.  Additional publications from this meeting will be posted on the Fisheries and Oceans Canada Science Advisory Schedule as they become available.

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