Relative Weight (Wr) Status and Current Use in Fisheries Assessment and Management

Condition assessment is commonly practiced by fisheries personnel as one tool for evaluating fish populations and communities. Several noninvasive condition measures are available for use, including Fulton's condition factor (K), relative condition factor (Kn), and relative weight (Wr). The use of Wr as a condition measure has increased within several peer-reviewed journals. In 1995 to 1996, survey responses from agency personnel in 48 states indicated that 22 states used Wr as a standard technique, 18 states identified Wr use as occasional, whereas only eight states indicated no Wr use. The regression-line-percentile technique is recommended for developing standard weight (Ws) equations. There are currently Ws equations available for 52 species and three purposeful hybrids. Length-related trends in condition need to be evaluated prior to calculating a population mean Wr. Relative weight target ranges should be adjusted to meet specific management objectives. Relative weight values are influenced by seasonal dynamics. The uses of Wr may go beyond just a measure of fish “plumpness.” Relative weight can serve as a surrogate for estimating fish body composition, as a measure of fish health, and to assess prey abundance, fish stockings, and management actions.

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