Horizontal and vertical movement ecology of shortfin mako sharks Isurus oxyrinchus in coastal and offshore waters of Taiwan

The shortfin mako shark Isurus oxyrinchus , listed as Endangered on the IUCN Red List, is a key apex predator in pelagic ecosystems but remains poorly studied in coastal and offshore waters of Taiwan—a region of intense fishing pressure and limited spatial tracking data. We tracked 3 individuals (one female ca. 170 kg and 2 males ca. 40 and 50 kg) for 117-142 d using pop-up satellite archival tags (PSATs) which recorded temperature, depth and light levels and transmitted via Argos. One of the tags was also physically recovered and also yielded >3.8 million high-resolution data records at 3 s intervals. Sharks exhibited pronounced diel vertical migration, reaching maximum depths of 993.5 m, with apparent size-dependent differences in depth use: the largest shark consistently dove deeper and occupied the 200-300 m depth stratum more frequently. Maximum dive depth was significantly correlated with sea surface temperature, mixed layer depth, and spatial location. Deep-diving events were closely associated with encounters of anticyclonic eddies, suggesting that mesoscale oceanographic features influence foraging behavior. These findings are broadly consistent with observations from other ocean basins but represent the first high-resolution data set for this species in the coastal and offshore waters of Taiwan. By integrating fine-scale vertical movement data with environmental modeling, this study provides novel insights into how physiological traits, thermal ecology, and oceanographic variability shape the behavior of shortfin mako sharks. The results help fill a critical data gap for this regional population and provide essential information to inform stock assessments, habitat-based risk models, and bycatch mitigation strategies for this endangered species.