A tagging experiment as validation study on age and growth of Raja clavata (Linnaeus, 1758) in the South Adriatic Sea

Semi-direct validation studies represent the most commonly applied methodology for elasmobranch and an useful tool for understanding the yearly deposition pattern of bands laid down on their hard structure. This study evaluated the age and growth of the thornback ray, Raja clavata (Linnaeus, 1758) in the South Adriatic Sea and for the first time attempted an age validation through a tagging experiment. Eighty-three thornback specimens were tagged and released, of which two were recaptured with oxytetracycline marks clearly visible. Further 291 vertebral centra were sampled and used for age estimation purposes. The oldest female was estimated to be 12 years old (total length, TL, 89 cm), while the oldest male was aged 8 years (79.9 cm of TL). The band deposition after oxytetracycline injection and growth during the freedom period (about 1 year) were consistent with the applied age estimation method and the obtained growth results. Thus, the analysis of the vertebral centra of the two recaptured specimens confirmed the hypothesis of a single annulus deposition per year.