First telemetry insights into the movements and vertical habitat use of megamouth shark (Megachasma pelagios) in the northwest Pacific

• Published in: Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2024-10, Vol.212, p.104385, Article 104385
• Main Authors: Clerkin, P.J., Arostegui, M.C., Chiang, W.C., Lin, S.J., Miller, C.D., Braun, C.D.
• Format: Article
• Language: English
• Subjects: DVM; Filter feeder; Geomagnetic geolocation; HMMoce; Kuroshio Current; Lamniformes; PSAT; South China Sea
• ISSN: 0967-0637
• DOI: 10.1016/j.dsr.2024.104385

The megamouth shark (Megachasma pelagios) is one of the ocean's largest and most enigmatic elasmobranchs, with only a few hundred individuals ever recorded. Most of what is known about the species comes from rare fishery bycatch, stranding, or sighting events, precluding an in-depth understanding of its movement ecology. Here, we report the results from three megamouth sharks outfitted with pop-up satellite archival transmitting tags to assess the species' horizontal and vertical movement patterns. Deployments of 12, 58, and 244 d in duration provided the first direct evidence of multi-month fidelity to the waters east of Taiwan and seasonal movement out of the region. Depth and temperature data revealed a pattern of normal diel vertical migration, with the majority of the day spent in the mesopelagic zone and night in the epipelagic. Vertical habitat use suggests potential behavioral thermoregulation and was consistent with tracking of migrating mesopelagic prey across diel periods. We discuss the specialized analytical methods needed to reconstruct the spatial habitat use of deep-diving megamouth shark from tag sensor measurements of the magnetic field, as well as avenues for future research on this understudied megaplanktivore. •The first long-term horizontal and vertical movements of tagged megamouth sharks were reconstructed.•Tagged sharks exhibited diel vertical migration and potential behavioral thermoregulation.•Reconstructed spatial movements showed fidelity to offshore waters on the east coast of Taiwan.•Broad-scale movement of a tagged shark into the South China Sea was observed.