Science Advisory Report  2009/003

Potential Impact of Smallmouth Bass Introductions on Atlantic Salmon: A Risk Assessment

Summary

• Smallmouth bass is not an endemic species in the Maritime provinces but they are presently known from 188 lakes/rivers of Nova Scotia and 69 lakes and 34 rivers in New Brunswick.
• Smallmouth bass are found in eight lakes in the Gulf Region and the latest introduction was confirmed in 2008 in Miramichi Lake, the first record from the Miramichi River.
• When smallmouth bass are introduced into a water body, they prey heavily on smaller fish, can out-compete other fish species, and can become a dominant component of the food web.
• There is a high likelihood of widespread establishment of smallmouth bass in the Southwest Miramichi River and in the Gulf Region rivers in general.
• Watersheds with a sequence of lakes within the main stems of rivers or in close proximity to main stems would provide a better environment for broad watershed establishment of smallmouth bass and negative interactions would be enhanced.
• The overall risk to the aquatic ecosystem is considered to be high in the lake environment; smallmouth bass is expected to become a dominant component of the food web and to cause significant reductions in existing biota. The uncertainty is low.
• The overall risk is considered to be moderate in the riverine environment; a measurable decrease in abundance of native populations is likely to occur in most locations due to the establishment of smallmouth bass. The uncertainty is high.
• Riverine habitat is used preferentially by Atlantic salmon. Although the overall risk to salmon is considered moderate in the riverine environment, none of the consequences of smallmouth bass introductions will be positive for Atlantic salmon.
• The highest probability of controlling or eradicating non-native species is through the use of multiple approaches. The likelihood of success of controlling and/or eradicating the target species is reduced when control and eradication actions are delayed.

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