Computation of confidence intervals for the size‐frequency (Hynes) method of estimating secondary production1

An estimator of variance is described for production values calculated by the size‐frequency (Hynes) method. The number of sampling dates is identified as having an important influence on the variance estimate. A geometric mean is proposed to estimate the average weight of individuals when lost between size classes. In an example calculation, Ephemerella dorothea (Ephemeroptera) from North Branch Creek, Minnesota, had an annual production value of 8.5 g·m−2 wet and an approximate 95% confidence interval of 7.0–10.0. Similar calculations for Baetis sp. (Ephemeroptera) from the same river yielded an annual production value of 4.7 g·m−2 wet with a confidence interval of 3.6–5.8. Significant differences in annual production thus exist between these mayflies.