The utility of the caged fish method in the Canadian metal mining Environmental Effects Monitoring program

Environmental Effects Monitoring (EEM) for Canadian metal mines has been mandatory since 2004. The program regulates metal mines to describe the environmental effects of effluent discharges on fish, fish habitat, and the usability of fisheries resources in receiving aquatic habitats. Issues have arisen regarding methods for conducting fish population surveys, the means through which effects on fish are to be monitored. The currently accepted approach to fish surveys in the EEM program is limited by an inability to document fish residency and exposure to metal contaminants. Caged fish studies have been proposed as an alternative. Caging fish in specific reference and exposure locations eliminates fish residency and exposure uncertainties. Experiments showed that caging does significantly affect small-bodied fish. Weight and length declined in all studies, but growth in length and reproductive development were evident in caged fish. Diet changes caused by caging are a factor limiting the utility of the method. Malnutrition (juvenile caged fish) and starvation (adult caged fish) likely resulted from the caging treatment, but stress did not appear to be a significant factor in these studies. Future experiments to characterize the nature of cage-induced diet changes must be implemented before an evaluation of the method's utility in the Canadian metal mining EEM program is feasible. (Abstract shortened by UMI.)...