Assessing age-0 year-class strength of fast-growing largemouth bass in a tropical reservoir

Age-0 largemouth bass Micropterus salmoides were collected every 3 weeks from 1992 to 1994, every 6 weeks from 1995 to 1998, and about every 15 weeks from 1999 to 2000 by means of a handheld electrofisher in Lucchetti Reservoir, Puerto Rico. An extended hatching period (January to June) and a high (0.63-1.50-mm/d) juvenile daily growth rate required high sampling effort because age-0 largemouth bass recruited to the sampling gear between February and September. To assess whether the handheld electrofisher catch per unit effort (CPUE; fish/h) of age-0 largemouth bass was a reliable estimator of relative year-class abundance, we regressed the age-1 largemouth bass CPUE obtained with a conventional boat electrofisher between 1994 and 2001 on the CPUE of age-0 (< 150-mm) fish from the previous years. Simple linear regression analyses indicated that as much as 90% (P < 0.01; N = 7) of the variation in age-1 CPUE could be explained by age-0 mean CPUE. Early variation of year-class abundance of largemouth bass can be detected efficiently with the handheld electrofisher, thereby allowing early evaluation of management options.