The Effects of Micro-Scale Spawning Phenology On Recruitment of Bluegill

Abstract – Bluegill Lepomis macrochirus commonly exhibit fractional spawning (i.e., multiple peak spawning events each year), but the role of timing and the duration of spawning events on recruitment to the adult life stage is not well understood despite the importance of timing at earlier life stages. Our objective was to identify the importance of bluegill spawning phenology on adult recruitment. Larval bluegills (< 13 mm total length) were collected from Pelican Lake, NE using larval trawls for seven consecutive years (2004-2010).  A subsample of larval bluegill was aged from each sampling date to estimate hatch date.  Spawning phenology metrics measured each year included peak hatch date, hatch duration, beginning hatch date, and a truncated hatch duration that minimized the influence of only a few individuals that hatched at the beginning and completion of the spawning season each year. Spawning metrics were then related to relative abundances (i.e., CPUE) of different life stages, including fall age-0 juveniles, spring age-1 in April, and late spring age-2 in June. Our results indicated that hatch duration, beginning hatch date, and truncated hatch duration were not related to any life stage examined. However, peak hatch date was related to age-2 CPUE, and strong year classes were evident when peak hatch occurred after July 1. Bluegill spawning phenology appears to play some role in adult recruitment.  Future research is needed to understand the specific mechanisms that are most responsible for these patterns and to determine whether these factors are ubiquitous across systems.