Michigan Department of Natural Resources
Research and Development Report No. 220
Institute for Fisheries Research Report No. 1773, 1970
Estimation of Total Mercury in Lake St. Clair Walleyes
James B. Reynolds
Great Lakes Fishery Laboratory
U. S. Fish and Wildlife Service
Percy W. Laarman
Institute for Fisheries Research
Michigan Department of Natural Resources
Introduction.-Mercury contamination of biological systems has recently joined the fast-growing list of environmental problems of public concern. In March 1970, commercial fishing was banned in Ontario waters of Lake St. Clair because mercury residues in walleyes, Stizostedion vitreum vitreum (Mitchill), and certain other species exceeded the 0.5 ppm government “action level.” Also, sport fishing was limited to a catch-and-release basis in both Ontario and Michigan waters of the lake. Subsequent actions by the governments have curtailed mercury discharges into Lake St. Clair, but a substantial period may be required for natural degradative processes to reduce contamination of fish to a tolerable (i.e., less than 0.5 ppm) level.
Efforts to detect any significant reduction of mercury residues in Lake St. Clair fishes will require the systematic collection of samples at regular intervals. Since mercury analyses are expensive and often time-consuming, it is desirable to limit the samples to the minimum number required to detect real changes in residue levels. We examine here the question of sample size required for analyses of mercury in walleyes.