Estudio de edad y crecimiento de la raya hocicuda Dipturus chilensis (Guichenot,1848) en el Atlántico Sudoccidental (34º -55º LS y 52º -69º LW)
This paper deals with the age and growth parameters of the Southwest Atlantic beaked skate Dipturus chilensis, as well as with some reproductive features of the species. Samples of individuals inhabiting 34°-55°S and 52°- 69°W were analyzed. They were taken during surveys carried out by the National Institute for Fisheries Research and Development (INIDEP) research vessels, as well as by a landing sampling at Mar del Plata port. The fish age was determined by counting growth rings from thin sections of the vertebral centra of 414 fish ranging 24-110 cm (203 males) and 24-115 cm (211 females) total length. The vertebral sections were stained using cobalt hloride. Both average per cent error (APE=5.94) and precision (D=5.89) indexes suggested that the method used for estimating age in D. chilensis was precise enough. The marginal increment analysis (MIA) supported the hypothesis of an annual deposition of a pair of bands, which ended during the autumn months. The maximum ages observed in males and females were 21 and 25 years, respectively. After fitting the von Bertalanffy and the Gompertz growth models, the last one appeared to be the most appropriated to describe the growth of the species, whose parameters were estimated to be: L =114.32 cm; k=0.10 years-1; t0=4.95 years (males), and L = 149.05 cm; k=0.07 years1; t0=-8.11 years (females). The asymptotic length estimates of both males and females were closer to the observed values than those derived from the von Bertalanffy model. Growth differences between sexes were significant, the females reaching a larger size than males. On the basis of macroscopic examinations of the gonad development, age and length at 50% maturity were estimated to be 94.04 cm and 17.7 years (females) and 84.04 cm and 14.6 (males). These results indicate that D. chilensis is a long-living, slow growing and delayed maturating species, and therefore it is particularly vulnerable to suffer overexploitation if facing heavy fishing pressure.