Size at maturity and reproductive traits of shortfin mako, Isurus oxyrinchus, in the western and central North PacificPublished: 18 January 2011
Yasuko Semba , Ichiro Aoki and Kotaro Yokawa .
Shortfin mako, Isurus oxyrinchus, is a highly migratory shark with a worldwide distribution. Despite recent global concern and intensive ecological studies on this species, little is known about its reproduction, owing to a paucity of information on mature females. We investigated the size-at-maturity and reproductive traits of shortfin mako in the western and central North Pacific. Males attain maturity at a much smaller size (156 cm) than females (256 cm). The positive relationship between maternal size and litter size indicates that fecundity increases as the female grows. The seasonal trends in the gonadosomatic index of mature individuals and the presence of females in early pregnancy confirmed that mating occurs from spring to summer. From monthly changes in embryonic body lengths, averaged per litter, and the seasonal occurrence of neonates, we infer that parturition occurs from winter to spring and the gestation period is 9–13 months. There was a negative correlation between embryonic developmental stages and environmental temperature for females in various stages of pregnancy. The productivity of this species may be higher than previously thought, considering the estimated gestation period and size-related fecundity.
Marine and Freshwater Research 62(1) 20-29 doi:10.1071/MF10123