Reproduction and embryonic development of the blue stingray,Dasyatis chrysonota, in southern African waters

Abstract

Dasyatis chrysonotais perhaps the most common of the 14 whiptail stingray (Chondrichthyes: Dasyatidae) species known to frequent the temperate coastal waters of southern Africa and like other stingrays they possess life history characteristics that make them vulnerable to over-exploitation. First and 50% maturity (Dw50) were determined for 153 males and 204 females from the Eastern Cape Province of South Africa. Disc width (Dw) for first andDw50maturity was estimated at 392 mm and 395 mmDw, respectively for males and at 500 mm and 505 mmDw, respectively for females. The reproductive cycle of males, based on gonadosomatic (GSI) and hepatosomoatic (HSI) indices indicates that they are most active during the spring. Females appear to have an annual reproductive cycle with a maximum HSI occurring during the summer and autumn, but it declines steadily through the birthing season reaching a low in the late spring. Fecundity, following a nine month gestation period, averages 2.8 with a range of 1–7. Embryos at six different development stages are described.Dasyatis chrysonota, like other dasyatids, exhibit life history characteristics that make them vulnerable to overexploitation, therefore a precautionary management strategy is advised for this species.