Direct age determination by growth band counts of three commercially important crustacean species in Chile

Abstract

Management of commercially important crustacean stocks has been hindered by the inability to directly determine individual age. A lack of comprehensive age information leads to poor understanding of life history schedules, difficulty in estimation of parameters necessary for modeling population dynamics, and uncertainty in the determination of appropriate harvest levels. This study applied a novel direct age determination method based on band counts to three Chilean crustacean species: red squat lobster (Pleuroncodes monodon), yellow squat lobster (Curvimunida johni), and nylon shrimp (Heterocarpus reedi) for the first time. The growth bands were observed and counted in the endocuticle layer in thin longitudinal sections of the meso-cardiac ossicles of the gastric mills in the two squat lobster species and in the eyestalks of the nylon shrimp. Comparison of growth band counts with independent estimates of age strongly suggests that the bands form annually, thus providing a direct and accurate method of age determination in all of the species examined. Sex-specific growth curves were produced and demonstrated that the females grow at a slower rate than the males in the three species. Size and age-at-sexual maturity were also estimated. Application of this technique to known-age individuals will be necessary to validate band counts as indicators of chronological age.