Size at Maturity, Mating and Spawning in the Portunid Crab Scylla serrata (Forskål) in Natal, South Africa

Size at sexual maturity, and mating and spawning periods, were investigated in the portunid crab Scylla serrata in northern Natal, South Africa. Ninety-five percent of females which had undergone the pubertal moult had sperm in their spermathecae, indicating that they had mated. Post-pubertal moult females were therefore considered mature. Size at 50% maturity for females was estimated to be 123 mm carapace width (CW) which is considerably smaller than previously recorded in South Africa. Some females underwent a moult after the pubertal moult. Fifty percent of male crabs were producing sperm at a size of 92 mm CW, but males smaller than 115 mm CW did not mate. Mating occurred in all months of the year. Spawning appeared to occur throughout the year with peak activity from late spring to early autumn. The present minimum size limit of 114-115 mm CW in South Africa may not be adequate to protect stocks should they be subjected to heavy fishing pressure.