Fish mortality
Estimating natural mortality (M) is one of the most difficult and critical elements of a stock assessment (Hewitt et al. 2007).There are two basic approaches used to estimate natural mortality: tagging studies and growth parameters.Tagging studies are used in the Brownie Model, where multiyear tagging studies are used to estimate natural mortality based on recaptures: The Paulys Model (using growth parameters) is an indirect way of estimating natural mortality.Pauly’s original method was based on the correlation of M with von Bertalanffy growth parameters (K and L∞) and temperature (Gunderson 2002): In the Hoenigs method, M was inversely correlated with longevity across a wide variety of taxa (Hewitt and Hoenig 2005): Fishing mortality (F) can be estimated by dividing the catch by the mean stock size.Knowing these rates can help managers to set harvest limits to (MSY) maximum sustainable yield or (OSY) optimum sustainable yield to give the maximum benefit to the stakeholders of the resource.