First-Summer Survival of Largemouth Bass Cohorts: Is Early Spawning Really Best?

Abstract

Previous work has demonstrated that survival of largemouth bass Micropterus salmoides through the first year of life can be size dependent, favoring larger individuals. Because size, diet biomass, lipid accumulation, and ultimately overwinter survival of juveniles are typically positively related to age, early spawning is clearly advantageous. However, a true understanding of which largemouth bass cohorts contribute to the new year-class remains somewhat unclear because these conclusions have largely been based upon fish collected during summer rather than fish collected during spring. Conceivably, even earlier hatched cohorts of largemouth bass could have existed in many of these studies, and these fish may simply not have survived to the summer collection period. In order to assess this possibility, we quantified first-summer survival of largemouth bass cohorts collected during 1992 and 1993 in Auburn, Alabama, ponds (which were 2–5 ha each). Our results indicate that it is early-hatched cohorts that likely contribute to the new year-class. Although we found that early-hatched cohorts were lost between May and July, these losses were not attributable to age-dependent mortality; instead, sampling biases associated with avoidance of seines by older, larger young-of-year largemouth bass appear to have driven these shifts. In addition, because we found that size-dependent cannibalism during summer acted to remove smaller, later-hatched largemouth bass, early hatching may enhance survival during larval and early juvenile stages in southern systems (and not just during the winter period). Given this information, fishery managers may potentially be able to implement harvest regulations that are designed to protect large, early-spawning adults, thereby increasing the probability of producing a strong year-class by enhancing first-summer growth and, ultimately, recruitment to adult stages.