New observations on the reproductive biology of the pelagic stingray, Dasyatis violacea Bonaparte, 1832 (Chondrichthyes: Dasyatidae) from the Mediterranean Sea

Abstract

        Captures of the pelagic stingray, Dasyatis violacea, in three Mediterranean areas, Tunisian coast, Algerian coast and the southern coast of France allow to report about aspects of the reproductive biology of the species. Adult males and females were above 420 mm and 450 mm disk-width (DW), respectively, with the largest male and female being 580 mm DW and 5800 g, and 610 mm DW and 6000 g, respectively. Size at birth was 160-195 mm DW and 191-212 g. Females were not significantly heavier than males. The diameter of fully yolked oocytes ranged between 18-22 mm (mean 19.5±1.10 mm) and weighed 2.0-2.4 g (mean 2.1±0.12 g). Gestation lasted approximately four months. Two litters per year is a probable hypothesis but requires confirmation as embryonic diapause cannot be entirely excluded. A calculated chemical balance of development based on mean dry mass of fully yolked oocytes and of neonates is 47. This high value shows that D. violacea is a matrotrophic species. Ovarian fecundity, based on the number of ripe oocytes ready for ovulation, ranged from five to ten. Uterine fecundity, based on the number of eggs and/or embryos, ranged from two to seven. There was no relationship between size and either category of fecundity. Male and female embryos are equally distributed, but in the largest free-swimming specimens, females significantly outnumbered males.