Error in Estimation of Feeding Rates from Changes in Mean Body Mass

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Abstract
Because of nonlinear relationships between body mass and many parameters in energetics models, rates of food intake calculated from change in mean body mass (a typical application of energetics models) do not necessarily equal true mean rates of food intake calculated from individual changes in body mass. Using both hypothetical data and actual field data for largemouth bass (Micropterus salmoides) marked with individually numbered tags, we show that discrepancies increase with variability in body mass but are negligible (< 3.5%) in all cases examined. Biased estimates of change in mean body mass, such as might result from size-selective mortality or sampling gear, can lead to substantial errors in energetics model estimates of mean food consumption rates. Use of growth data for individually marked fish in conjunction with an energetics model permits calculation of confidence intervals, statistical comparison of food consumption rates, and examination of relationships between foraging success and individual body mass.