Reproductive biology of the blue shark (Prionace glauca) in the western North Pacific Ocean

The reproductive biology of the blue shark (Prionace glauca) in the western North Pacific Ocean was
investigated to contribute to future stock assessments because of limitations of recent studies and the lack of information
about the reproductive cycle. Reproductive data were obtained from 490 males (precaudal length (PCL), 33.4–252.0 cm)
and 432 females (PCL, 33.4–243.3 cm). Size at 50% maturity was estimated to be 160.9 cm for males and 156.6 cm PCL
for females. Litter size varied from 15 to 112 (mean 35.5) and was positively correlated with maternal PCL. Parturition,
ovulation and mating occurred sequentially from spring to summer. The gestation period was estimated to be 11 months.
The ovarian follicles of pregnant females developed synchronously throughout the gestation period along with embryonic
growth, indicating that females reproduce annually. Our results showed that the productivity of North Pacific blue sharks is
higher than previously thought, based on larger fecundity and a shorter reproductive cycle. These new findings will
improve future stock assessments and provide management advice.