Ontogenetic and Sex-Specific Isotopic Niches of Blue Sharks (Prionace glauca) in the Northwestern Pacific
2025
Pengpeng Ding | Satoshi Katayama | Hiroaki Murakami | Tah Andrew Ryan
The blue shark (Prionace glauca) is a pelagic species widely distributed in the northwestern Pacific Ocean. The trophic roles of blue sharks across different developmental stages and between sexes remain poorly understood. Fifty-four sharks were sampled (October 2022&ndash:March 2024) for precaudal length (PCL) and stable isotope levels (&delta:13C, &delta:15N) in the muscle tissue (n = 52). Mean PCL varied based on the month of sampling (p = 0.034), with the smallest individuals occurring in July (143.0 ±: 4.3 cm) and the largest in October (178.0 ±: 2.6 cm). Stable isotope analysis (&delta:13C and &delta:15N) indicated consistent offshore habitat use (&delta:13C: from &minus:20.70 to &minus:18.82&permil:) and significant nitrogen isotopic differences among life history (&delta:15N: from 10.23 to 15.72&permil:: Kruskal&ndash:Wallis test, p = 0.037). The elevated &delta:15N values observed in the subadult group (relative to juvenile individuals) are likely due to trophic enrichment associated with morphological development. Females exhibited markedly larger isotopic niches (SEAc = 2.42&permil:2) than did males (0.57&permil:2), and niche overlap was greater within each sex (40&ndash:52%) than between sexes (<:21%). These results revealed sex-specific ecological roles and trophic strategies throughout the life history of P. glauca. Understanding these foraging differences can help with catch reduction and habitat-protection measures in the transboundary pelagic fisheries of the northwestern Pacific.
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