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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13557

Seasonal migrations of pregnant blue shark Prionace glauca in the northwestern Pacific

Yuki Fujinami*, Ko Shiozaki, Yuko Hiraoka, Yasuko Semba, Seiji Ohshimo, Mikihiko Kai

*Corresponding author:

ABSTRACT: Information on the movements of highly migratory species is important to understand their ecology including habitat use, population connectivity and stock structure, to implement appropriate management and conservation measures. The blue shark Prionace glauca (Carcharhinidae) is highly migratory, has a global distribution, and is ecologically and economically important as one of the most abundant apex marine predators. The migration patterns of pregnant blue sharks were unknown. We use pop-up satellite archival tags (PSATs) to elucidate seasonal migration of pregnant blue sharks in the northwestern Pacific. Of 24 tagged adult females, archival data were subsequently obtained for 21 of them (141.1–243.3 cm precaudal length). Of these, 17 were confirmed to be pregnant at the time of release, using ultrasonography or analysis of sex steroid hormones. Females with small embryos moved in a northeasterly direction, from subtropical (10–30°N) into temperate (30–40°N) waters during autumn and the following spring; two of these females returned to subtropical waters in spring and summer. In contrast, females with large embryos moved in a southwesterly direction, from temperate into subtropical waters during spring and autumn. Tagged sharks also manifested regional differences in diving behaviors, reflecting thermal habits in the ocean environment. Our findings indicate that pregnant blue sharks undergo a seasonal northeast–southwest migration within a year to give birth to pups in productive temperate waters. We report the first seasonal reproductive migration of pregnant blue sharks in the global ocean.