Reproductive biology of the thornback ray Raja clavata (Chondrichthyes: Rajidae) from the coast of Languedoc (Southern France, Northern Mediterranean)

The thornback ray, Raja clavata L., 1758 had a wide Atlanto-Mediterranean distribution. However at present captures of the species showed a constant decline, especially off the coast of Languedoc (southern France, northern Mediterranean) where rare specimens were caught throughout the year. The smallest male and female adults were 420 mm and 540 mm disc width (DW), respectively and weighed 2130 g and 4950 g, respectively. The largest male and the largest female were 5 10 mm and 690 mm DW, respectively and weighed 4500 g and 5980 g, respectively. There was a significant relationship of total mass versus DW between males and females. The diameter of the largest yolky oocytes ranged from 24 to 27 mm (mean = 25.9 +/- 0.9) and weighed from 3.2 to 3.7 g (mean = 3.5 +/- 0.2). Vitellogenic activity occurred practically all year round, a bit less in April and August. Production of egg cases was observed throughout the year, except in April and August. Egg cases had between 122 and 127 mm (mean: 124.1 mm +/- 1.3) in length with horns; and between 61 and 66 mm (mean: 63.6 mm +/- 1.4) in length without horns, their width were between 50 and 56 mm (mean: 52.9 mm +/- 1.5) and they weighed between 19.5 and 22.5 g (mean: 20.9 g +/- 1.4). Fecundity remained difficult to assess, an estimation based on production of egg cases and/or number of yellow yolky oocytes during year counted in adult females, enable to consider it between 108 and 262.