Seasonal residency and large-scale return migration patterns of basking sharks in high-latitude environments of the North Atlantic

Marine megafauna adopt diverse movement strategies to balance the costs and benefits of migration amid shifting environments, resources, and reproductive demands. Species with broad latitudinal ranges can exhibit distinct movement patterns at the edges of their distribution. However, pan-latitudinal perspectives on annual movements remain scarce, as exemplified by the planktivorous basking shark Cetorhinus maximus, for which most data derive from temperate waters near the range centre. We satellite-tracked 13 basking sharks tagged near their northern distributional limit in northern Norway for up to 515 d to investigate year-round horizontal and vertical movements. Six of 7 sharks, each tracked for ≥338 d, performed large-scale return movements — departing the Norwegian shelf after summer, occupying the West European Basin and adjacent waters during winter, and returning to the Norwegian Sea the following summer. Individuals covered annual distances averaging ~14 000 km, including one transatlantic movement to the southern Sargasso Sea. Vertically, sharks exhibited irregular surface use and isobath tracking in boreal shelf habitats, and mesopelagic occupancy with diel vertical migration in lower-latitude oceanic waters, consistent with known prey distributions. Seasonal movements averaged 30° of latitude, exceeding those of lower-latitude conspecifics, thereby providing first evidence of ‘leapfrog migration’ in basking sharks. These comparably consistent latitudinal movements likely track large seasonal shifts in prey availability within a 2–25°C thermal envelope. As climate change and other anthropogenic pressures alter marine habitats and phenologies, these findings advance understanding of range-edge movement dynamics and underscore the value of long-term, pan-latitudinal studies for assessing population connectivity and guiding dynamic conservation strategies for this endangered megaplanktivore.