Resumen del producto

Natural mortality estimates constitute one of the most challenging problems in fisheries science. Most methods are empirical and involve estimation based on exploited ages. Tagging experiments or consumption data can also yield such estimates. However, these approaches can be expensive or complex to apply continually. In this paper, we propose an approach to estimate natural mortality-at-length based on data from unexploited stocks (virgin stocks or stocks during closed seasons). The approach is based on a transition matrix in which growth probabilities are based on the von Bertalanffy equation and elements of the survival matrix are given by e-^M?t. The input data required are vectors of length-frequency distributions representing the stock abundance at different times. The solution is found by applying a least squares algorithm The approach is illustrated by applying the method to data on the Venus clam Chione californiensis during the closed season (approximately eight months). Natural mortality-at-length tends to decrease with length. This tendency was observed every month, but its parameters (intercept and slope) showed a seasonal pattern. Natural mortality-at-length and at-time is explained in terms of the dynamics of the life cycle. Density-dependent effects are also indicated.

Palabras clave: Natural mortality-at-length; projection matrix; Venus clam; Chione californiensis

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