Ovoviviparous, with litters of 1 to 21 young (Ref. 247, 88865). Mating probably occurs in winter. Gestation period of 18 to 24 months, longest known of all chondrichthyans (Ref. 26346). Size at birth 18-30 cm (Ref. 26346). In the northeast Atlantic, pups are born in winter, with size at birth about 26-28 cm (Ref. 88864). Sex ratio at birth is 1:1. Gravid females congregate in enclosed shallow bays to give birth (Ref. 247). The mother shark experiences a series of rhythmic contractions, just like in mammals, and the young are delivered head first. Larger older females have bigger litters with larger pups; a female with 100 cm TL carries on average 4 times as many embryos compared to a 70 cm female and the former have higher survival rates than those born to small females (Ref. 4856, 88869, 88883).