Long-distance migrations by marine vertebrates are often triggered by pronounced environmental cues. For the endangered basking shark (Cetorhinus maximus), seasonal changes in water temperature are frequently proposed as a cue for aggregation within (and dispersal from) coastal hotspots. The inference is that such movements reflect year-round occupancy within a given thermal ‘envelope’. However, the marked variance in timing, direction and depth of dispersal movements hint at a more nuanced explanation for basking sharks. Here, using data from pop-off archival transmitters deployed on individuals in Irish waters, we explored whether autumnal decreases in water temperature triggered departure from coastal habitats and how depth and location shaped the sharks’ realised thermal environment over time. Temperature was not an apparent driver of dispersal from coastal seas, and variance in daily temperature ranges reflected occupancy of different habitats; coastal mixed/stratified and offshore subtropical/tropical waters. Furthermore, individuals that moved offshore and into more southern latitudes off Africa, exhibited a distinct daily cycle of deep dives (00:00–12:00, 200 m–700 m; 12:00–00:00, 0–300 m), experiencing a more extreme range of temperatures (6.8–27.4 °C), including cooler minimum temperatures, than those remaining in European coastal habitat (9.2–17.6 °C). Collectively, these findings challenge the supposition that temperature serves as a universal driver of seasonal dispersal from coastal seas and prompts further studies of deep-water forays in offshore areas.

海洋脊椎动物的长距离迁徙通常是由明显的环境线索触发的。对于濒临灭绝的姥鲨（Cetorhinus maximus），经常提出水温的季节性变化作为沿海热点聚集（和分散）的线索。推断是这样的移动反映了给定热“包络”内的全年入住率。然而，散布运动的时间、方向和深度的显着差异暗示了对姥鲨的更细致入微的解释。在这里，使用部署在爱尔兰水域个人身上的弹出式档案发射器的数据，我们探讨了水温的秋季下降是否会引发离开沿海栖息地，以及随着时间的推移，深度和位置如何影响鲨鱼的实际热环境。温度不是沿海海域扩散的明显驱动因素，每日温度范围的变化反映了不同栖息地的占用；沿海混合/分层和近海亚热带/热带水域。此外，向近海移动并进入非洲更南纬地区的个人表现出明显的每日深潜周期（00:00-12:00、200 m-700 m；12:00-00:00、0-300 m） ，经历了比欧洲沿海栖息地（9.2-17.6°C）更极端的温度范围（6.8-27.4°C），包括更低的最低温度。总的来说，这些发现挑战了温度是沿海海域季节性扩散的普遍驱动因素的假设，并促进了对近海地区深水袭击的进一步研究。经历比欧洲沿海栖息地（9.2-17.6°C）更极端的温度范围（6.8-27.4°C），包括更低的最低温度。总的来说，这些发现挑战了温度是沿海海域季节性扩散的普遍驱动因素的假设，并促进了对近海地区深水袭击的进一步研究。经历比欧洲沿海栖息地（9.2-17.6°C）更极端的温度范围（6.8-27.4°C），包括更低的最低温度。总的来说，这些发现挑战了温度是沿海海域季节性扩散的普遍驱动因素的假设，并促进了对近海地区深水袭击的进一步研究。