Paleolimnological reconstructions of long-term changes in fisheries status in Sudbury area lakes

Long-term fisheries data are often lacking for small lakes. This is certainly true in Ontario's Sudbury region, where many lakes currently lack fish, presumably because of impacts from local mining and smelting operations. If rehabilitation of such lakes is being considered, it is prudent to have knowledge of their past fisheries status. We assessed the fisheries history of some lakes in the Sudbury region using the sedimentary remains of Chaoborus larvae. Among six recently fishless lakes, Bat Lake is a bog that apparently has never supported fish populations, and data were inconclusive for Ruth-Roy Lake. In Swan, Hannah, Middle, and Clearwater lakes, fish apparently disappeared during either the 1940s or 1950s when pH levels were declining and metal concentrations were increasing. Hannah and Middle lakes were limed in the mid-1970s, and pH levels have remained circumneutral. Fish have since recolonized both lakes. Crowley Lake currently supports fish; it apparently always supported fish, and no conclusion could be made as to whether its yellow perch (Perca flavescens) were introduced. Where total fish losses were indicated, the disappearances coincided with pH values less than or equal to 5.0 inferred from diatom and chrysophyte analyses, levels at which fish reproduction is usually unsuccessful or severely depressed.