Science Advisory Report  2010/065

Science advice from the risk assessment of New Zealand mud snail (Potamopyrgus antipodarum) in Canada

Summary

• The non-indigenous New Zealand mud snail (Potamopyrgus antipodarum) was discovered in British Columbia in 2006 but had been reported from Lake Ontario in 1991.
• A number of life history traits enable New Zealand mud snail to be very effective invaders including: high fecundity; asexual reproduction; low susceptibility to predators; and tolerance to a wide range of environmental conditions.
• Many vectors and pathways associated with the introduction and spread of these small snails have been identified but there is high uncertainty associated with the importance of each. Most introduction pathways are human-mediated so outreach efforts should be directed here to minimize further introduction/spread.
• Ecological niche modeling and water chemistry inferred from bedrock geology suggest the probability of establishment (survival and reproduction) is very high for a substantial portion of Canadian fresh and brackish waters (exception being the Arctic) despite the potential for models of this type to underestimate the potential distribution of an organism.
• The probability of arrival was generally high to very high with the exception of the Arctic and Atlantic coastal waters where it was deemed this probability was low. However, the probability of a widespread New Zealand mud snail invasion generally was low to moderate with the exception of the Gulf of Mexico drainage (high) and the Great Lakes/St. Lawrence (very high: snail already in much of this unit).
• Potential impacts of New Zealand mud snail were derived from the limited literature and expert opinion and are expected to vary with the density of established populations. Generally biological impacts of a widespread invasion were considered very low/low with the exception of freshwater biodiversity where the impact was deemed higher (moderate).
• the overall risk posed to Canadian aquatic ecosystems by New Zealand mud snail was determined to be low to moderate but with very high uncertainty.
• To reduce the uncertainty associated with this risk assessment, additional research on the biology of Canadian populations of New Zealand mud snail is required, especially to better characterize impacts on our ecosystems.
• Although the overall risk was deemed relatively low based on a widespread New Zealand mud snail invasion in each of the assessed units, it is likely the risk at smaller spatial scales (not considered in the risk assessment) could be substantially higher.

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat Pacific National Advisory meeting of March 24-25, 2010 on the Biological risk assessment of New Zealand mudsnail in Canada (Centre of Expertise for Aquatic Risk Assessment – CEARA). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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