Development of a standard weight equation for juvenile steelhead trout and effects of temperature, turbidity, and steelhead trout biomass on relative weight

Standard weight equations were developed for juvenile steelhead using the regression line percentile and empirical methods. The equation developed using the empirical method better represented juvenile steelhead lengths and weights and was free of length bias. Standard weight was used to estimate average relative weights for juvenile steelhead trout populations in northern California streams. Population averages of relative weight, estimated by the empirical equation, were then modeled against turbidity, temperature, and juvenile steelhead trout density to determine if these variables had meaningful relationships with condition. Average relative weight measured in the fall was positively related to degree day accumulation during late winter and early spring. Turbidity and biomass metrics were not found to be significantly related to juvenile steelhead trout condition. Further research is needed to determine if relative weight accurately represents the effects of physiological, population and environmental variables on juvenile steelhead trout condition.