Science Advisory Report 2010/082

Science Advice from a Risk Assessment of Largemouth Bass (Micropterus salmoides) in British Columbia

Summary

• Largemouth Bass is a voracious piscivore known to cause changes in ecosystem structure in lakes into which it has been introduced. It is responsible for local extinctions of small prey fishes and declines in minnow species’ richness.
• It is occurs in both lake and river habitats and some individuals are found to move long distances, while others are territorial which may limit their spread.
• Largemouth Bass is native to eastern North America and likely first invaded British Columbia from authorized introductions in Washington State in the late 1800s. Whether Largemouth Bass qualifies as an invasive species in British Columbia that warrants new management strategies depends on the extent of negative impact posed to the invaded ecosystems.
• A risk assessment was conducted to estimate the threat posed to British Columbia’s salmonid populations and aquatic ecosystems by the introduction of Largemouth Bass. The risk assessment addressed the likelihood of introduction (arrival, survival, establishment and spread) as well as the ecological consequences to the native biodiversity and ecosystem functioning, should Largemouth Bass become established. The risk assessment also assessed the threat posed by these species as vectors for diseases and parasites.
• The likelihood of survival, reproduction and spread was considered very high with very low uncertainty on Vancouver Island and the lower mainland, it was considered high with low uncertainty in the upper Fraser, Thompson and Columbia regions and was considered low with moderate uncertainty in the Arctic, central coast and north coast regions.
• The overall risk was assessed to be very high with low uncertainty in small waterbodies and moderate with moderate uncertainty in large waterbodies. The risk of genetic consequence is considered very low with low uncertainty.
• The ecological impacts caused by introduction of parasites and diseases were determined to be low with high uncertainty.
• Largemouth Bass has specific habitat requirements that may limit establishment and spread.

This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of March 4-6, 2008 on Risk assessment of spiny-rayed fishes (six species).  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

Complete document (PDF, 246 KB)

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