A Method for Correcting the Relative Weight (Wr) Index for Seasonal Patterns in Relative Condition (Kn) with Length as Applied to Walleye in Wisconsin

Abstract

AbstractWe determined whether the relative weight (Wr) model for walleye Sander vitreus was representative of populations in Wisconsin and if relative weight varied with length seasonally. We then developed standard condition (Kn) models that correct for seasonal variation in body condition. We compiled data from 54,657 walleyes sampled during 640 surveys of 202 lakes in 30 Wisconsin counties. Weight–length relationships and mean relative weight varied more widely for Wisconsin populations than for North American populations overall. Weight–length relationships and mean relative weight varied significantly among seasons, with the highest slope (lowest intercept) and mean relative weight in spring, lowest slope (highest intercept) and mean relative weight in early summer, and intermediate slopes (and intercepts) and mean relative weights in late summer and autumn. Mean relative weight increased with length in spring, decreased with length in early summer, and did not change with length in late summer, autumn, or over all seasons combined. For samples collected in spring or early summer, we found that relative weight did not accurately index body condition or estimate trends in body condition with length. We propose a new index, adjusted relative weight (the product of Wr and a seasonal Kn model, Wr · Kn) that adjusts relative weight for life‐history‐based seasonal trends in body condition with length.