Abstract:

Wild yellow perch (Perca flavescens) were sampled from five lakes in each of two metal contamination gradients in Sudbury, ON (n = 1324) and Rouyn-Noranda, QC (n = 1125) in the spring and summer of 2002 and 2003, respectively, in order to examine growth patterns, longevity, and the single and combined influences of season, region, and position along each metal contamination gradient on fish condition. Growth patterns varied by contamination gradient; fish from Rouyn-Noranda began rapid growth at a young age, whereas fish from Sudbury lakes showed slow growth rates between ages 0-3, after which growth rates improved. Slopes of double-log plots of fish weight and lengths varied between the two study regions when all fish were considered together and when the analysis was restricted only to non-contaminated reference lakes. Fish from contaminated lakes grew faster and died younger than fish from reference lakes in both contamination gradients. Observed growth patterns are likely due to increased food consumption in metal-contaminated lakes, as a compensatory means of replacing lost electrolytes from chronic metal exposure. Fish from Sudbury had lower condition than those from Rouyn-Noranda, higher condition occurred in the summer than in the spring, and fish from contaminated lakes had lower condition than those from cleaner lakes. However, when condition was studied at the level of individual lakes within each contamination gradient, condition variability was too high to draw any meaningful conclusions. Tissue Zn accumulation appeared to correlate with fish condition. However, tissue Zn concentrations demonstrate strong temporal stability, and it is more likely that Zn covariates, such as Cd or Cu (both of which are much less temporally stable in fish tissues) actually influenced condition. These results suggest that long-term processes are more important than short-term processes for establishing growth patterns, longevity, and fish condition in metal-contaminated systems.

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