Recovery of Marked Fish following a Second Poisoning of the Population in Ford Lake, Michigan

In 1936, a 10.7‐acre lake in Otsego County, Michigan, was treated with rotenone to eliminate a population of stunted yellow perch. An attempt to recover the entire population yielded 4,817 stunted perch, 27 trout in poor condition, and four species of minnows. The weight of what was assumed to be the total population was 516 pounds or slightly more than 50 pounds per acre. In 1937, an experimental planting of Montana grayling was made which was not successful owing to unauthorized introduction of bluegills about the same time. In 1941, 5,000 fingerling brook trout were stocked, but proved unable to compete with the rapidly increasing bluegill population and disappeared 4 years later. In 1943, walleyes were introduced in the hope of reducing the bluegill population to a point where survivors could make satisfactory growth. In 1946, when rotenone reappeared on the civilian market, the lake was treated with poison again, and an attempt made to recover the entire population. The total weight of fish recovered was 1,293 pounds, or 111.5 pounds per acre, more than twice the poundage found in 1936; the difference perhaps can be explained by bluegills being closer to the primary food chain than yellow perch. Of greater interest were the findings on completeness of recovery. Four and 3 days, respectively, prior to poisoning, 246 bluegills and 210 brook trout were fin‐clipped and planted. Only 58.9 percent of the marked bluegills and 44.7 percent of the marked trout were recovered despite careful search. Considerable doubt is thereby cast on the prevalent practice of assuming practically complete recovery of fish populations following rotenone treatment, and figures on total fish production derived by this method.