Like other requiem sharks, the spinner shark is viviparous. Adult females have a single functional ovary and two functional uteri; each uterus is divided into compartments, one for each embryo. The embryos are initially sustained by a yolk sac. When the embryo grows to around 19 cm (7.5 in) long, the supply of yolk has been exhausted and the empty yolk sac develops into a placental connection through which the mother provides nutrients for the remainder of gestation. Females give birth to three to 20 (usually seven to 11) pups every other year, after a gestation period of 11–15 months. Mating occurs from early spring to summer, and parturition from March to April in the northwestern Atlantic. Young are birthed in coastal nursery areas such as bays, beaches, and high-salinity estuaries in water deeper than 5 m (16 ft). The length at birth is 66–77 cm (26–30) in the northwestern Atlantic. Spinner sharks are relatively fast-growing sharks: 30 cm (12 in) per year for newborns, 25 cm (9.8 in) per year for one-year-olds, 10 cm (3.9 in) per year for adolescents, and 5 cm (2.0 in) per year for adults. In the northwestern Atlantic, males mature at 1.3 m (4.3 ft) long and females at 1.5–1.6 m (4.9–5.2 ft) long, corresponding to ages of 4–5 years and 7–8 years, respectively. The maximum lifespan has been estimated at 15–20 years or more.
The spinner shark is a fast, active swimmer that sometimes forms large schools, segregated by age and sex. Young individuals prefer cooler water temperatures than adults. Off South Africa, females are found close to shore year-round while males only appear during the summer. Smaller spinner sharks may be preyed upon by larger sharks. Known parasites infest the shark’s gills, the skin, the nares and the rear margins of the fins.