Estimation of Fish Populations in Michigan Lakes

Abstract

Fish population estimates, using trap nets in the Petersen mark-and-recapture procedure, were made during 1948, 1949, and 1950 on Sugarloaf Lake in Washtenaw County and during 1950 on Fife Lake in Grand Traverse County, Michigan. The nets were of two sizes: 3-foot and 6-foot. The lake acreages are 180 and 575, respectively. The important fish species were bluegill, pumpkinseed sunfish, yellow perch, largemouth bass, smallmouth bass, black crappie, northern pike, yellow and brown bullheads, and warmouth. The study was limited to fish over 6 inches in length. In four separate netting periods, 17,887 fish (approximately half bluegills) were marked by fin clipping and released, and 2,991 of these (17 percent) were recaptured. Distinctive markings were used for fish from two halves of each lake, and recaptures were tabulated accordingly. Marked fish, liberated at a common release station near the center of the lake, showed a tendency to return to the same half of the lake where marked; but the amount of this “homing” was not sufficient to invalidate the population estimations. Distinctive marking for two groups of stations, separated systematically according to even and odd numbers in series, gave returns which showed no marked tendency for fish to return to their home trap-net site. The three separate estimations of populations of legal-size fish in Sugarloaf Lake, computed by the Schumacher and Eschmeyer formula, gave 17,648 fish for the fall estimate of 1948, a total of 15,531 fish for the spring estimate in 1949, and 22,178 fish in the spring of 1950. These totals, correlated with the numbers of trap-net stations on which the estimates were based (30, 20, and 40, respectively) suggest, by extrapolation, that the true population figure is something less than 30 thousand. The average computed total for the 3 years was 18,452 fish, or 102 fish and 43.1 pounds per acre. Estimations by the Schnabel formula gave totals which were generally a little higher than by the Schumacher and Eschmeyer formula. For Fife Lake the estimated total population was 99,056 fish or 172 fish of 62.3 pounds per acre. In both lakes the bluegill made up over half of the totals. Records of marked and unmarked fish in anglersˈ creels immediately following the trap netting provided another basis for estimating the fish populations in Sugarloaf Lake in 1949 and 1950. Such estimates were about double the estimates based on trap-net recaptures. The reason for the difference was not determined.