Basking sharks (Cetorhinus maximus) are the second largest fish in the world, yet we still know surprisingly little about where they go and what they do once they disappear from surface waters. A new study fills some of those gaps thanks to some tagged basking sharks who were blinged out with high-tech gear off the coast of northern Norway to allow scientists to track their movements across an entire year.

These animals, which feed on microscopic zooplankton, are usually spotted cruising near the surface in summer months, often around rich feeding grounds. But once the feeding season is over, their next moves have remained something of a mystery, especially in high-latitude regions like the Arctic where climate change is already transforming the ocean landscape. By using pop-up satellite archival tags, researchers were able to follow these sharks well beyond the usual study windows, gathering high-resolution data that revealed just how dynamic and adaptable these animals can be.

Two female basking sharks have provided particularly detailed migration tracks. One left the chilly Arctic waters and traveled all the way to the beautiful Azores in the central Atlantic before returning north, completing a round-trip migration spanning thousands of miles. The other female did something quite different, staying north of the Arctic Circle through much of the winter and only moving to the North Sea in the spring. These vastly differing paths illustrate just how variable shark behavior can be, even within the same species and tagging location. Both individuals, however, showed an impressive ability to tolerate a wide range of ocean temperatures. One was recorded diving into sub-zero waters (a first for this species!), stretching the known limits of this shark’s thermal limits and shows how they might cope with rapid environmental shifts.

By collecting data every five seconds, the recovered tags also offered an unprecedented view into how these sharks use their environment. In deeper oceanic waters, they followed a pattern known as diel vertical migration — rising toward the surface at night and sinking during the day — likely to track zooplankton that do the same to avoid predators. But their behavior over continental shelf regions was more erratic and shaped by the seafloor, local water layers, and prey availability. Zooplankton are influenced by light levels, temperature gradients, and ocean features like fronts and currents, and the sharks seemed to align their movements with these prey-driven cues. In some areas, they dove deep during the day to follow food. In others, they tracked bioluminescent events, showing how finely tuned their behavior is to their surroundings. This kind of behavioral flexibility (or "plasticity") may be what helps basking sharks survive in such a fast-changing world.

Unlike many large marine species that are restricted to certain habitats or temperature bands, basking sharks seem to be able to tolerate a broad thermal range and switch up their foraging strategies depending on where they are. That makes them more resilient in theory… but also harder to protect. As global climate change alters ocean temperatures, currents, and food web dynamics, these sharks will likely need to keep adjusting their movements. But unless we understand what drives those movements now, it will be hard to predict where they’ll go in the future or what new risks they might face along the way.

Like other large marine megafauna, basking sharks play an important role in shaping ocean ecosystems. Although they do not eat other large animals like top predators do, they are still considered keystone species because of how they influence plankton populations and energy flow in the ocean. These gentle giants also share something else with animals like whales and sea turtles: wide-ranging movements that take them across international boundaries and into areas increasingly affected by human activity. Fishing, shipping, pollution, and warming seas all threaten their survival. And because these sharks are endangered, understanding when and where they’re most at risk is a conservation priority. Their adaptability gives them a fighting chance, but conservation measures still need to account for the full range of habitats they use, including those in remote or deep-water regions.