The application of this should consider several features of shrimp populations related to biotic and abiotic components of natural mortality, reproductive strategies and any effects of accumulated mortality throughout shrimp life cycle. An accurate estimation of the natural mortality is a basic requirement (Gracia, 1995), and a bias in the estimation of this parameter has important consequences in fisheries management (Gracia, 1989b). In the case of postlarvae and juvenile stages the problem is more complicated as reliable estimations of natural mortality are scarce, so this parameter is considered to be high (without considering the effect of migration). According to Alvarez et al. (1987) juvenile migration in a given area can bias mortality by around 25%. When this bias is not considered, it could influence calculations on shrimp extraction and management strategies.