Abstract
Examination of the reproductive biology of Mustelus asterias in the north‐east Atlantic Ocean highlighted apparent geographical variation in maturity, fecundity and ovarian cycle between Atlantic and Mediterranean populations. The stretch total length ( L ST ) and age at 50% maturity for Atlantic males and females were estimated at 78 cm L ST and 4–5 years and 87 cm L ST and 6 years, respectively. Size at maturity of females was considerably smaller than in Mediterranean specimens (96 cm L ST ). Ovarian fecundity ranged from eight to 27 oocytes and uterine fecundity from six to 18 embryos. The gestation period was c. 12 months, followed by a resting period of c. 12 months, resulting in a biennial cycle. Females stored sperm in the oviducal gland and, unlike Mediterranean specimens, no uterine compartments were observed in Atlantic specimens. This study reveals the existence of strong, possibly adaptive, divergence in life‐history traits in an elasmobranch, whose northern populations may be more susceptible to overexploitation than previously believed.