Reproductive biology of the Caribbean sharpnose shark, Rhizoprionodon porosus, from northern Brazil

Abstract

Two hundred and seventy three Caribbean sharpnose sharks,Rhizoprionodon porosus, were collected from catches of vessels fishing with gill-nets off the coast of northern Brazil between April 1996 and July 1997. The total sex ratio post partum was significantly biased towards females (1:1.57), but significantly more immature males than immature females were sampled (1.45:1), indicating sexual segregation. Females and males were categorized into reproductive stages according to changes in their reproductive tract. Size at sexual maturity for females was estimated to be ˜65 cm total length (TL), and males matured at between ˜65 and 70 cm TL. Gravid females had 1 to 8 embryos that approached a size at parturition of between ˜33 and 37 cm TL. The sex ratio of embryos was significantly biased towards females (1:1.79). Positive linear relationships were detected between TL of mature females and ovarian and uterine fecundities. Concurrent ovulation and gestation cycles and a clear relationship between embryonic development and maturation of the ovary showed that females are ready to copulate immediately after parturition. Reproduction occurs annually ,and although a peak in copulation was detected between late winter and early summer, many females appear capable of mating at any time throughout the year.