Re-Examination of Four Empirical Estimators of Natural Mortality Rates for Fish– Do They Stand the Test of New Data?

Despite widespread and persistent application of various empirical estimators of natural mortality rate, a comprehensive evaluation of their predictive ability is still lacking. Hence, are all these estimators equally good? Also, with improved ageing techniques and updated estimates of mortality and growth, we might ask how robust are empirical estimators that were constructed based on age and growth studies that are at least 30 years old? We focus on four estimators: Pauly’s (1980) method based on von Bertalanffy growth parameters (K, L_∞) and mean water temperature, Hoenig’s (1983) method based on maximum age, Alverson and Carney’s (1975) method based on K and maximum age, and Jensen’s (1996) method based on K. We searched the literature and obtained direct estimates of natural mortality rates with matching sets of life history parameters for close to 200 fish stocks. We address the following: 1) do the coefficients in these estimators change much when the models are refitted to the new data, 2) which estimator best reproduces the mortality estimates? Preliminary results suggest the estimators are generally robust but that Hoenig’s estimator has higher predictive ability than Pauly’s, which works better than the Jensen and Alverson-Carney estimators.