Three methods for estimating production forgone were compared by assessing the effects of power plant entrainment and impingement on gizzard shadDorosoma cepedianumin western Lake Erie. The three approaches evaluated were (1) the Rago (1984) method, which is a direct method based on exponential mortality and growth, (2) a continuous-time direct method based on exponential mortality and the von Bertalanffy growth equation, and (3) an indirect method, based on exponential mortality and the von Bertalanffy growth equation, in which production forgone was calculated as the difference between population production with and without an environmental disturbance. The indirect method gives a measure of the relative effect of the power plant-induced mortality and production, but requires estimation of recruitment, which is difficult to estimate. An initial estimate of production forgone by the direct approach of Rago (1984), which does not require an estimate of recruitment, can be used to estimate recruitment for the indirect estimate of production forgone; together, the direct and indirect approaches give a more complete assessment of production forgone. A sensitivity analysis showed production forgone was sensitive to changes in mortality rates of larvae, young of the year, and juveniles and to change in the asymptotic weight of adults.
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