In the Arctic Ocean, survival is determined not only by ice cover, but also by light. A recent study from Greenland shows that ringed seals appear to closely link their diving behaviour to daylight cycles and the movements of their prey. Once again, this highlights how finely tuned ecological interactions are within the Arctic food web.
Researchers analysed high-resolution dive records from three ringed seals that had previously been tagged with satellite transmitters and later recaptured. Unlike standard telemetry data, the team had access to complete depth measurements recorded every four seconds, a level of detail that often disappears in the compressed datasets transmitted via satellite.
Adults follow the rhythm of their prey
The data reveal clear differences between the animals. Two adult females repeatedly dived at specific times of day and depths, a pattern strongly suggesting targeted foraging. Particularly striking was that the dive profiles of one seal from southeast Greenland closely matched the daily vertical migration of capelin (Mallotus villosus), an important prey fish. These fish schools remain at greater depths during the day and move higher in the water column at night.
The seals appeared to respond directly to this behaviour, diving more frequently and precisely into the depth ranges where prey were concentrated during daylight hours. This suggests that ringed seals actively adjust their hunting strategy to the vertical movements of their prey, a classic example of finely tuned predator-prey dynamics in a marine ecosystem.
Differences between habitats also played a role. In fjord systems with limited depth, dives remained correspondingly shallow, while animals in more open coastal waters reached significantly greater depths. Local seabed topography therefore indirectly shapes the seals’ hunting strategy by influencing the vertical distribution of prey.
Juveniles dive less strategically
A young male behaved differently. His diving patterns showed no clear daily rhythm and appeared comparatively random. Researchers interpret this as evidence that efficient hunting strategies may need to be learned. Only with increasing experience do the animals seem to systematically exploit the daily migrations of their prey.
Active by day, resting at night
Across all three animals, another pattern emerged: calmer, less active dives occurred more frequently at night. This suggests that ringed seals concentrate their main hunting periods during brighter hours, even in the low-light conditions of the Arctic autumn and winter season.
Implications for understanding Arctic ecosystems
The study underscores how strongly Arctic predators are shaped by the interaction of light conditions, prey dynamics, and habitat structure. Even small changes, such as shifts in plankton blooms, altered fish distributions, or increasing sea-ice loss, could disrupt these finely balanced patterns.
In a rapidly changing Arctic, such high-resolution behavioural data provide valuable clues as to how sensitive marine food webs may be. Ringed seals are considered a key species in many Arctic ecosystems, meaning their behaviour is more than just a zoological detail. It is an indicator of the condition of the entire system.
Marcel Schütz, PolarJournal