Reproduction in the Sandbar Shark, Carcharhinus plumbeus, in the Waters off Northeastern Taiwan

Abstract

The purpose of this study was to investigate the reproductive biology of sandbar sharks, Carcharhinus plumbeus from northeastern Taiwan waters. A total of 885 sandbar sharks was examined. The size of 50% maturity in sandbar shark is taken to be 170-175 cm and 175 cm for females and males, respectively. The number of embryos per litter ranged from four to 12, with a mean of 7.54. Pregnant individuals containing six, seven, or eight embryos constituted 59 (80%) of the 74 females examined. Of 558 embryos in 74 litters examined, 274 were female and 284 were male. The null hypothesis of a 1:1 sex ratio is not rejected at the 0.05 level. Pups are born from Feb. to April. We estimate the gestation period to be 10-12 months. Most embryos had attained a total length of about 60-65 cm after 10-12 months of development, at which size they could be readily separated from the placenta, suggesting that they were full term and ready to be born. The relationship between the total number of uterine embryos and the total length of mother is roughly described by the regression equation (n = -7.544 + 0.075 TL; n = 74; r = 0.41). Although it is clear from this regression that fecundity is related to the size of the mother, the relationship is not particularly strong. We find that fertilization occurs during April and May, two months prior to the estimate reported by Taniuchi for C. plumbeus in Japanese waters.