Long-term Monitoring of Fish Communities in Acid Sensitive Lakes in Ontario

A monitoring program began in 1982 to establish baseline data from which to assess long-term effects of acid deposition on fish communities in 20 low alkalinity (0–2.6 mg/L) lakes in south-central Ontario. The study lakes were all clear (dissolved organic carbon < 4 mg/L and dilute conductivity > 35 μS/cm), but differed in size (11–607 ha) and fish community composition (2 to 18 species). Monitoring included assessment of fish species presence, abundance, age composition, growth, recruitment, and angler harvest. Field toxicity tests were used to test the direct toxicity of lake or runoff water to sensitive life stages of various indigenous fish species. A description of the sampling procedures and some current findings from this ongoing study are presented.