Distribution and reproductive biology of the spinner shark, Carcharhinus brevipinna (Muller and Henle, 1841) (Chondrichthyes : Carcharhinidae)

The spinner shark, Carcharhinus brevipinna, is a Lessepsian immigrant formerly common in the Gulf of Gabes (southeastern Tunisia, central Mediterranean). It migrated northward into the Gulf of Tunis as a consequence of competition pressure from its sympatric species, the sandbar shark, C. plumbeus. Adult males and females reach over 1720 mm and 1960 turn total length (TL), respectively. The largest known male and female are 2630 mm and 2750 mm TL, respectively. There is no significant relationship of mass versus TL between males and females. C. brevipinna is a placental viviparous elasmobranch. Adult females have a single functional ovary and two functional uteri, in which encapsulated eggs and embryos are equally distributed. Mating occurs in spring or early summer; parturition, in August. Gestation lasts 13-14 months or longer, and there is a seasonal reproductive cycle. Vitellogenesis proceeds in parallel with gestation. Diameter of the largest yellow-yolked oocytes ranges from 31 to 36 mm (33.3 mm +/- 1.4); and weight from 9.1 to 9.9 g (9.5 g +/- 1.6). The placenta is definitively established after the embryos reach 185 min TL. Both uteri are compartmentalized in chambers, and a single embryo develops in each chamber. Size at birth and mass at birth, based on fully developed fetuses and the smallest free-swimming specimens (neonates) are 610-690 mm TL and 1060-1850 g, respectively. A chemical balance of development based on mean dry masses of the largest yellow-yolked oocytes and the fully developed embryos is 65.8. This is the highest value ever computed in a viviparous elasmobranch, indicating that C brevipinna is a matrotrophic species. Ovarian fecundity is higher than uterine fecundity. There is no significant relationship between the two categories of fecundity and female TL. Litter size ranges from 6 to 10. The sex ratio of embryos is 1:1. Male neonates are significantly more numerous than female, in contrast with juveniles and adults. The relative abundance of pregnant females and neonates suggests that the Tunisian coasts could be considered a nursery area for the spinner shark.