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- Skates and rays diversity, exploration and conservation - case-study of the thornback ray, Raja clavataPublication . Serra-Pereira, Bárbara; Gordo, Leonel Serrano, 1957-; Figueiredo, Ivone, 1960-Skates have been increasingly exploited in recent decades despite their recognized vulnerability to fishing (due to their life-history traits), and regardless of a lack of basic knowledge about their biology. The present thesis contributed to a great advance in the knowledge about skates in Portuguese waters, with special attention to the most abundant and commercially important species, the thornback ray Raja clavata. The main aims of the present thesis were to study: (i) skate fishery; (ii) skate biodiversity; and (iii) biological traits of the thornback ray. Skates are mainly caught by the artisanal fishery, and a fishing segment targeting skates was identified. They are landed in three mix species categories, and this incorrect identification has misleading a fluctuation in fish abundance of nine skate species. The blonde ray was the most abundant in landings, followed by the thornback ray and the undulate ray. Species were easily discriminated using the mitochondrial gene cytochrome c oxidase subunit I. The thornback ray was the species with the highest intraspecific genetic variability. Size conversion factors were obtained for six skate species, and proved to be helpful to discriminate between them. The thornback ray, blonde ray, spotted ray and cuckoo ray have generalized diets, feeding mainly on benthic prey, and changing their preferred prey items during their ontogenetic development. Dermal denticles were considered more accurate than vertebrae to assess age and growth of thornback ray. This species has a slow growth rate (k = 0.117 year–1), large maximum size (L∞ = 1280 mm), late maturation (L50, F= 784 mm, around 8 years of age; L50, M= 676 mm, around 6 years of age) and low fecundity (140 eggs per female per year). Great advances on the knowledge of the reproduction of this species were achieved, namely on the definition of reproductive phases and the development of the different reproductive structures. In conclusion, this thesis was pioneering in several fields of study, namely in the utilization of the COI gene to discriminate between NE Atlantic skate species, in the use of dermal denticles for ageing thornback ray and in describing the development of the oviducal gland of a skate species. In the future, it will be essential to extend the findings achieved in this thesis to the remaining species occurring in Portuguese waters, filling the gap of information about these fish for the southern region of the NE Atlantic, and to contribute to their accurate assessment.