Search

The thornback ray Raja clavata is one of the most abundant bycatch species of trawl fishing in the waters of the Gulf of Gabes, but little is known about its life history in this area. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. The age of individuals was estimated by counting growth bands on central vertebral sections. Marginal increment and edge analysis supported the hypothesis of annual deposition of growth bands, with the opaque band formed during autumn. The parameters estimated from von Bertalanffy and Gompertz growth functions showed differences between sexes. The oldest thornback ray female was aged 15 years (104 cm TL), whereas the oldest male was 12 years (89 cm TL). Variations in the gonadosomatic and hepatosomatic indices of both sexes and the presence of vitellogenic activity in mature females during the year indicated that the species cannot be considered to be a continuous spawner. Males were found to mature between 55 and 75 cm TL, whereas females matured between 72.4 and 85 cm TL. The TL at which 50% of the population reached maturity was 67.44 and 81.42 cm for males and females, respectively. Males and female thornback rays mature, respectively, at approximately 5.3 and 7 years old.

The feeding ecology of the thornback ray, Raja clavata, was studied based on the analysis of the stomach contents of specimens caught in the south-eastern Black Sea, Turkey, between May 2003 and January 2004. A total of 198 thornback rays were analysed to describe food habits and investigate the effect of sex, size and season on diet. Thornback rays fed mainly on teleost fish (especially red mullet, Mullus barbatus ponticus) and mud shrimp (Upogebia pusilla). Other prey included harbour crab, whiting, shrimp larvae and others. No differences were observed between dietary composition of males and females, but significant differences were found between size classes and seasons.