Rosa, A. Age and growth of the thornback ray, Raja clavata (Linnaeus, 1758), in the Azores Archipelago.

Age and growth of the thornback ray, Raja clavata (Linnaeus, 1758), was studied by whole-view and interpretation of vertebral growth bands in 202 individuals. These vertebrae were obtained from 568 specimens captured by longline during ground fish survey cruises in the Azores Archipelago during the Springs of 1995, 1996, 1997 e 2001. A preliminary study was done, in order to compare 5 different techniques used for enhancing vertebral bands. It resulted in the selection of the cobalt nitrate technique (modified by Duarte, 1999). This technique proved to be the most simple and efficient in the enhancing of growth bands in the thornback ray, and it was used in the following study. The estimated ages ranged from 0 to 10 years. The von Bertalanffy growth curve was estimated for both sexes combined and the estimated parameters were Linf=161,87 cm, k =0,06 year-1 and t0=-3,03 year. The growth of thornback ray was back-calculated via two proportional methods: the Dahl-Lea and the Fraser-Lee methods. Length-frequency analysis with MULTIFAN was used to estimate growth parameters indirectly. For the validation of estimated ages, a comparison was made between the different methods, which showed some concordance between the curves resulting from the empirical method and MULTIFAN. A comparison was also made between the present study and those of other authors. The results obtained in this study were similar to those of Ryland & Ajayi (1984).