Relations between Stock and Environmental Variables, and an Index of Abundance, for Juvenile Alewives and Blueback Herring

Abstract

Abstract The maximum of a series of catch-per-unit-effort (CPUE) estimates was postulated to be less biased as a juvenile abundance index (JAI) by the seasonal downstream migration of juvenile anadromous alewives Alosa pseudoharengus and blueback herring A. aestivalis than a timeaveraged or summed CPUE. The JAI for blueback herring was adjusted for outlier CPUE values occurring in response to high nighttime illumination (moon phase moderated by cloud cover). The JAI was not significantly related to spawning stock abundance, population fecundity, or year-class size even though spawning stock size was correlated with year-class size and future adult returns and juvenile densities were estimated with relatively good precision (±7–15% error). Dischargeinduced bias in the JAI masked intermediate-stage stock-recruitment relations. The validity and usefulness of an index of abundance for juvenile Alosa spp., as obtained by push-net survey methods, are doubtful. Small sample sizes and high variability of biologic...