Angler's Harvest, Growth Rate and Population Estimate of the Largemouth Bass of Browns Lake, Wisconsin

Abstract

An apparent abundance of largemouth bass (Micropterus salmoides) below legal length in Browns Lake, Wisconsin, led to an experimental liberalization of angling regulations in which the minimum size limit was eliminated and the open season was lengthened. As a start towards the evaluation of these measures a study has been made of the angler's harvest and of the growth rate of the bass, and the size of the bass population has been estimated.

A partial creel census indicated that an angling pressure amounting to 75 hours per acre harvested a total of 2,671 largemouth bass in 30,091 hours. Sixty-two percent of the largemouth bass were over 10 inches long and 38 percent less than 10 inches, the former minimum legal size. The earlier opening of the season permitted capture of more large individuals.

The relationship between the anterior scale radius (inches × 44) and the total length (inches) of largemouth bass was described satisfactorily by the equation S = 0.1813 L^1.3613. Calculations of growth in length based on this relationship were made by a nomograph for 889 angler-caught and 881 seine-caught fish. Largemouth bass reached a size of 10 inches in 3 to 4 years. Age-groups IV and V dominated the catches.

The total population of largemouth bass was estimated by the mark and recapture technique to include 21,980 fish over 6 inches long. The validity of this estimate was confirmed independently by DeLury's method involving a time series of catch-effort statistics. The estimated population amounted to 55.5 individuals or 33.3 pounds per acre, a figure similar to most reported for other stocks. Angling mortality was estimated at 12 percent and total mortality at 24 percent.