AUTHORS: Derek Ogle and Ian Winfield TITLE: Ruffe Weight-Length Relationships with a Proposed Standard Weight Equation
ABSTRACT: Ruffe Gymnocephalus cernuus length-weight data from 141 data sets were obtained from a variety of waters across Europe and the Laurentian Great Lakes for summarization and development of standard weight (Ws) equations. The mean slope of the length-weight relationship from all populations and all but the 95th percentile were not different from three, suggesting that ruffe growth is generally isometric. The Ws equations developed using the regression line percentile (RLP), linear empirical percentile (EmP), and Froese’s methods exhibited length-related biases. The quadratic EmP Ws equations for the 75th and 50th percentiles did not exhibit length-related biases and, thus, can be used to compute the relative weight of ruffe. The EmP 75th percentile Ws equation was log10(Ws75) = -2.5800 + 0.6210*log10(TL) + 0.6073*(log10(TL))2 and the 50th percentile Ws equation was log10(Ws50) = -3.3524 + 1.3969*log10(TL) + 0.4054*(log10(TL))2 when constrained to ruffe between 55 and 205 mm total length (TL). We propose that minimum TL for a five-cell length categorization system used to compute stock indices for ruffe be 55, 90, 120, 140, and 175 mm, respectively. These results provide a method for computing relative weight indices for typical (50th percentile) and above average (75th percentile) ruffe that will allow comparisons of body condition across time, among habitats, among bodies of water, and among length categories.
CITATION: Ogle, D.H. and I.J. Winfield. In press. Ruffe weight-length relationships with a proposed standard weight equation. North American Journal of Fisheries Management XX:XXX-XXX. Preprint PDF