Fall abundance of age-0 largemouth bass is more important than size in determining age-1 year-class strength in Illinois

Because of physiological limitations associated with energy reserve depletion of smaller individuals, first winter survival of juvenile largemouth bass Micropterus salmoides has been proposed to be highly dependent on size at the end of the first growing season. The relationship between the mean size of prewinter age-0 largemouth bass and relative survival through the first winter was assessed in seven northern Illinois impoundments. In each of these impoundments from 1988 to 1991, age-0 largemouth bass were sampled using AC electrofishing techniques during early fall (late, September/early October), and then again in the following April. For each collection of age-0 largemouth bass we determined the catch-per-unit effort (CPUE), total length, and condition. Within a given year there was substantial variation among lakes in the mean size of age-0 largemouth bass, but limited variation among years for a given lake. The postwinter/prewinter relative abundance of largemouth bass was determined annually for each reservoir. The hypothesis that postwinter abundance of age-0 largemouth bass is strongly related to prewinter size was not supported by our data. Instead, in northern Illinois impoundments, it appears that postwinter abundance of largemouth bass is dictated by the abundance of age-0 fish at the end of the first growing season, regardless of size.