The reproductive biology of the sandbar shark, Carcharhinus plumbeus (Chondrichthyes: Carcharhinidae), from the Gulf of Gabès (southern Tunisia, central Mediterranean)

Abstract

The sandbar shark, Carcharhinus plumbeus, is commonly captured in the Gulf of Gabčs (southern Tunisia). Of 932 specimens collected from January 2001 to May 2004, the smallest mature male was 1545 mm total length and the largest male was 1935 mm. All males above 1600 mm were mature. Adult females ranged 1660-2815 mm, while all females above 1720 mm were mature. The pupping season occurred in spring and early summer, with parturition in July. Gestation was estimated at twelve months, with females appearing to reproduce in alternate years. The diameter of the largest yellow-yolked oocytes ranged 29-32 mm (mean 30.3±1.2) with the mass ranging 9.1-13.3 g (mean 11.9±1.3). Both uteri were compartmentalized into chambers and a single embryo developed in each chamber. Length and weight at birth, based on near-term embryos, were estimated at 450- 650 mm and 532-1458 g. The chemical balance of development, based on the mean dry masses of the largest yellow-yolked oocytes and near-term embryos, was 40.3, showing that C. plumbeus is a matrotrophic species. Ovarian fecundity was slightly higher than uterine fecundity. There was a positive relationship between uterine fecundity and total length of females. Litter sizes ranged 4-10 (mean 6.9±1.1). Embryos and free-swimming juvenile and adult females significantly outnumbered males.