The adequacy of empirical estimates of natural mortality (M) for the Patagonian scallop Zygochlamys patagonica (King & Broderip, 1832) is assessed against a direct estimate based on catch-at-ago data obtained from fishery research surveys and auxiliary information on fishing effort exerted by the commercial fleet. Based mostly on growth parameter information resulting from the von Bertalanffy equation, we obtained empirical estimates of M based on formulas commonly used in fisheries assessment and quantified variation in their estimates though parametric bootstrapping. The modal values of direct estimates of M was 0.38/y, with a 95% confidence interval in the range 0.09–0.77/y. Estimates obtained with empirical models were close to direct estimates. In particular, a model developed for invertebrate species (Arce's model) was very close both in point values and variability. Our results suggest that for this species, the empirical estimates, which are easily obtainable and broadly used in many fisheries, can be reliably used when no other estimates are available. However, we contend that in other cases their use should be limited to species when the performances of empirical methods were compared with direct evaluations of M.
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Vol. 29 • No. 2