Estimation of natural mortality in two demersal squat lobster species off Chile

Abstract

AbstractNatural mortality (M) is a key parameter for understanding population dynamics, especially in relation to harvested populations. Direct observations ofMin crustaceans are scarce, due to the moulting process. Indirect methods to estimateMwith easier-to-obtain life history attributes are therefore used routinely. Given their theoretical background, we reviewed the applicability of these methods for crustaceans. We applied the selected methods to two crustacean species harvested in Chilean waters: the yellow squat lobster (Cervimunida johni) and red squat lobster (Pleuroncodes monodon). Uncertainty of eachMestimate was incorporated in the life history parameters that input into the indirect method (trait-error) and parameters defining the indirect method (coefficient-trait-error). Methods based on the relationship between total mortality and maximum age, or with different ages and based on life history theory were the most appropriate for crustaceans since they apply across taxa.Mestimates showed high variability between species, sexes and areas. Estimations ofMforC. johnivaried from 0.13 to 0.28 (year−1) for males and 0.17 to 0.51 (year−1) for females. ForP. monodonvalues for the north varied from 0.26 to 0.37 (year−1) for males and 0.24 to 0.45 (year−1) for females. In the south, values ofMwere higher for both males (0.43–0.68 year−1) and females (0.41–1.06 year−1). High variability in theMestimates was associated with the method and number of parameters, their uncertainty, theoretical background and probability distribution.Mestimates are not comparable, raising the need to propagate the uncertainty ofMinto the stock assessment of Chilean squat lobsters.