Relationships between Annual Variations in Reservoir Conditions and Age-0 Largemouth Bass Year-Class Strength

Abstract

Variable recruitment has been documented in populations of largemouth bass Micropterus salmoides throughout the species' range. Shoreline electrofishing was used from 1988 to 1998 to assess the magnitude of variations in year-class strength of largemouth bass at the time cohort mean lengths reached 50 mm in Jordan Lake, North Carolina. Concurrent measures of adult stock characteristics, dynamics of larval and juvenile shad Dorosoma spp., lake elevation dynamics, and seasonal air temperatures were used to test published findings concerning factors that influence largemouth bass year-class strength. Catch rates of juvenile largemouth bass varied fourfold from 1988 to 1995. No significant relationships were observed between largemouth bass year-class size and spawning stock size, shad dynamics, or variations in lake elevations. However, late-winter and early spring air temperatures explained a significant amount of the observed variation in catch rates of age-0 largemouth bass. Abundance of yearling largemouth bass in early spring also varied significantly among years and was significantly correlated with differences in age-0 abundance at 50 mm the previous year, suggesting that differences in abundance established early in the life history of largemouth bass play a significant role in recruitment variation. Although relative year-class strength varied predictably with prespawn air temperatures, long-term trends indicated a decline in relative year-class strength over the course of 11 years. Broadscale factors, such as temperature, may introduce variation about the expected mean year-class size of largemouth bass in Jordan Lake, which can be further modified by variations in local conditions.