Stages When Year-class Strengths are Established for Walleye and White Bass

Determining the life-history stage when year-class strength is established is critical for effective management of sportfish populations.  Recruitment is often considered to be the most influential factor governing fish populations and is inherently less consistent in systems with high intra- and interannual variability, such as irrigation reservoirs.  We collected walleye and white bass from irrigation reservoirs and used Spearman rank correlation of relative-abundance indices at three life-history stages to determine when year-class strength was established.  Early juvenile walleye abundance was correlated to late juvenile walleye abundance, and larval white bass abundance was correlated to early juvenile white bass abundance; no other correlations existed.  We conclude that year-class strength for walleye in these systems was established by the early juvenile stage, and that year-class strength for white bass in these systems was not established by the early juvenile stage.  Thus, managers could increase the effectiveness of walleye stockings by introducing fish after the early juvenile stage rather than before.