Comparison of the Beverton-Holt and Ehrhardt-Ault mortality estimators: a simulation approach and implications for tropical fisheries

Many length based methodologies are appealing due to their potential application in data-poor situations.  In this study we evaluate two length based mortality estimators for potential biases through a simulation model.  A hypothetical population of fish ages was generated from the exponential distribution, with a known instantaneous total mortality rate, Von Bertalanffy growth parameters and different levels of variability.  The primary goal is to compare the performances of the methods of Beverton-Holt versus Ehrhardt-Ault in estimating total mortality values with varying sample sizes and when the ages for truncation are not known perfectly.  Other simulated scenarios included varying values of total mortality rates and specification of growth parameters, with the aim of assessing the utility of these methods and their biases given a spectrum of life history strategies. Preliminary results showed that both methods have a greater potential for bias for long-lived species which generally have lower mortality rates.