Atlantic white-sided dolphins make surprising journeys across the ocean

For the first time, scientists have documented Atlantic white-sided dolphins (Leucopleurus acutus) crossing the North Atlantic Ocean, revealing previously unknown long-distance movements and identifying a key feeding area in the Irminger Sea between Greenland and Iceland.

A journey across an ocean

Researchers used satellite tags to follow 23 dolphins tagged in the Faroe Islands and discovered that three dolphins independently swam more than 1,000 kilometers westward to the Irminger Sea. They maintained steady speeds of around 4 kilometers per hour for 5 to 11 days straight, an endurance feat comparable to running multiple marathons back-to-back.

Two dolphins remained in the Irminger Sea for weeks, one for 26 days and another for 63 days before their tags stopped transmitting in late autumn. Their route wasn’t random but followed a highly productive “corridor” under Iceland where nutrient-rich waters created by deep mixing support abundant life, from tiny zooplankton to whales. Think of it like following a sushi conveyor belt through the ocean.

Their destination, the Irminger Sea, appears to serve as an important autumn feeding ground, with deep water mixing up to 1500 meters that fuels a rich ecosystem. The dolphins’ extended stays and their movement patterns in this area suggest they were there to feed, rather than just passing through.

Diving deep for dinner

The study also revealed impressive diving capabilities. While most dives were shallow (under 100 meters), dolphins regularly dove to 400-600 meters, much deeper than previously recorded for this species. The deepest dive reached 616 meters: about twice the height of the Eiffel Tower.

Diving patterns followed a daily rhythm: shallow dives during the day and deeper, longer dives at night. This matches the behavior of prey like lanternfish that migrate toward the surface at night and become more accessible for the dolphins.

After being tagged together, dolphins separated within days, reflecting the species’ fluid social structure and supporting genetic evidence of a single, connected population throughout the central and eastern North Atlantic.

An important feeding area that should be protected

The Irminger Sea emerges as an important habitat for marine life, yet it lacks formal protection despite supporting dolphins, whales, seabirds, and commercially important fish.

This matters particularly because climate change is rapidly altering the North Atlantic. As ocean warming strengthens stratification (layering) and reduces nutrient mixing in many areas, the Irminger Sea’s deep winter mixing could become an increasingly vital refuge for marine life. Some fish species, like mackerel and blue whiting, have already shifted their distribution patterns in response to changing conditions, moving toward these nutrient-rich waters.

What’s next for Atlantic white-sided dolphin research?

The study was limited to summer and autumn, leaving winter and spring movements unknown. Only a handful of dolphins provided long tracking records, and dive data came primarily from a single individual. Year-round tracking could reveal whether these trans-Atlantic journeys are seasonal and identify other important habitats.

The findings highlight how satellite tracking of top predators like dolphins can uncover biologically hotspots that might otherwise remain invisible. As the researchers note, understanding where marine mammals go, and why, is essential for protecting them in an era of rapid environmental change.

For these dolphins, the message is clear: some of the ocean’s most important feeding grounds lie far offshore, in international waters where protection requires cooperation across nations. The journey to safeguard these travelers may be as challenging as the journeys they make.

Sources and further reading

• De Clerck, S., Hátún, H., Mikkelsen, B., Ugarte, F., & Heide-Jørgensen, M. P. (2025). Trans-Atlantic movements of Atlantic white-sided dolphins, Leucopleurus acutus. Frontiers in Marine Science.