Estimation of mean movement rates for blue sharks in the northwestern Pacific Ocean
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Animal Biotelemetry Open Access
Estimation of mean movement rates for blue sharks in the northwestern Pacific Ocean Mikihiko Kai* and Yuki Fujinami
Abstract Background: The blue shark Prionace glauca is a highly migratory species with a circumglobal distribution. Mean movement rate, defined by the horizontal tracking distance between two data points over the duration of time, is commonly used to understand the horizontal displacement of highly migratory species across a wide range. However, the estimation of mean movement rates for blue sharks has never been conducted using a statistical model. We therefore investigated the mean movement rates using a generalized linear mixed model with data from satellite tags to estimate the range of mean movement rates for 10 blue sharks in the northwestern Pacific Ocean and to reveal the interaction of mean movement rate with several factors. Results: (1) Estimations of mean movement rates for the 10 blue sharks were significantly influenced by behavioral differences among individuals; (2) uncertainty in the estimation (i.e., predictive and confidence intervals) of mean movement rates for these blue sharks was larger over shorter time periods, and (3) the predictive intervals of mean movement rates for the sharks ranged widely from 0.33 to 5.02 km/h. Conclusion: Blue sharks are considered to opportunistically change their mean movement rates regardless of differences in sex, movement direction, or season. Keywords: GLMM, Highly migratory shark, Movement rates, Satellite tagging, SPOT-tag Introduction The blue shark Prionace glauca is a highly migratory species inhabiting oceanic and circumglobal waters from temperate to tropical regions [1]. Understanding the horizontal movement patterns of animals is essential in the development of conservation and management measures, because such knowledge aids in clearly assessing their habitat use as well as their stock structure [2–6]. Satellite tags such as smart position only or temperature transmitting tags (SPOTs) and pop-up satellite archival tags (PSATs) are highly versatile location trackers commonly used to investigate the movement of highly migratory species such as tunas, billfishes, and sharks [e.g., 7–9]. The movement patterns of blue shark have been globally *Correspondence: [email protected] Fisheries Resources Institute, Japan Fisheries Research and Education Agency, 5‑7‑1 Orido, Shimizu‑ku, Shizuoka, Shizuoka 424‑8633, Japan
investigated using these tags [e.g., 10, 11], however such information from the western and central North Pacific Ocean is still lacking [7]. Mean swimming speed (MSS) is one of the vital parameters for understanding the behavior ecology of pelagic sharks [12]. The values for blue shark had been estimated globally using ultrasonic acoustic telemetry, and the resulting observed range was from 1.3 to 3.7 km/h [13–15]. The data-loggers with biologging sensors (e.g., speed, acceleration, and depth/temperature) enable us to observe swimming behavior in three dimensions and to reco
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