Document Type



Virginia Institute of Marine Science

Publication Date



Data report (Virginia Institute of Marine Science); no. 63


Mean length-based methods to estimate instantaneous total mortality rates, Z, are important assessment tools for data-poor stocks. One commonly used method was developed by Beverton and Holt (1956). The behavior of this method, especially in relation to bias, has been fairly well characterized. Another method by Ehrhardt and Ault (1992) was proposed to "correct" the Beverton-Holt (BH) method for applications to length frequency distributions that are truncated at the upper end. The Ehrhardt-Ault (EA) method has zero bias at equilibrium when there is no variability in length at age but the reliability of the method has not been demonstrated under conditions of reasonable magnitude of growth variability. It is also unclear how one would determine the best input value for the upper length truncation parameter. This report presents additional simulation results to supplement the results in Then et al. (2015). The estimators, evaluation criteria, simulation procedures, and conditions simulated are given in Then et al. (2015).


This report presents additional simulation results to supplement the results in: Then, A. Y., J. M. Hoenig, and T. Gedamke. 2015. Comparison of two length-based estimators of total mortality: a simulation approach. Transactions of the American Fisheries Society. doi: 10.1080/00028487.2015.1077158.



Fish populations, Fishes--Mortality

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Creative Commons Attribution 3.0 License
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