Reproductive Biology and Distribution of the Blue Shark (Prionace glauca) in the Western Indian Ocean

Due to the limited biological research on the blue shark in the Indian Ocean, such as the lack of a clear understanding of its reproductive biology and distribution, our study analyzed and evaluated the fork length distribution, sexual maturity length, reproductive capacity, and spatiotemporal distribution of blue sharks based on biological data and capture location information collected in the western Indian Ocean from 2010 to 2020. The objective of this study is to provide reliable biological information important in performing future stock assessments vital for species conservation in this region. A total of 791 male (33-249.5 cm FL) and 803 female (12-349.6 cm FL) blue sharks were collected in the West Indian Ocean. We used the morphology of the sexual organs to ascertain their sexual maturity. Results show that the observed size at 50% sexual maturity of male blue sharks in the West Indian Ocean was 161.4cm FL (192.4 cm TL) for males and 179.3 cm FL (213.9 cm TL) for females based on logistic curve analysis. The average litter size of pregnant blue sharks was 33.7 pups. There were significant differences in the distribution of blue shark individuals with different sexual maturity levels in different quarters (p < 0.05). This study suggests that the area near the equator in the Indian Ocean from October to March of the following year may be the mating ground for blue sharks, while the temperate waters in the Indian Ocean are the nursery ground and parturition ground for pregnant and juvenile throughout the whole year. Therefore, it is recommended to adopt a more scientific and reasonable operational method in these areas.

Automated summary

This study analyzed and evaluated the distribution, sexual maturity, reproductive capacity, and spatiotemporal distribution of blue sharks in the western Indian Ocean based on biological data and capture location information. The results provide important biological information for future stock assessments and species conservation in the region. The study suggests that the equatorial area in the Indian Ocean may be the mating ground for blue sharks, while temperate waters serve as the nursery and parturition ground for pregnant and juvenile blue sharks throughout the year.