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A new study led by McGill University researchers indicates that humpback whales in the southeastern Pacific combine real-time environmental cues with their memories of conditions in their Antarctic feeding grounds to determine when to embark on their annual 10,000-kilometer journey. With climate change accelerating, the researchers warn this strategy may become less effective amid shifting ocean conditions.

The research team analyzed eight years of satellite tracking data, from 2009 to 2016, from 42 humpback whales tagged off Costa Rica, Panama and Ecuador. Their goal was to track each individual during their migration to the Southern Ocean in Antarctica and to understand what triggers the whales' southward migration each year.

The findings suggest that whales integrate local environmental changes—such as sea temperature and food availability—with their long-term memory of ocean conditions in their Antarctic feeding grounds. This helps them time their migration to coincide with the seasonal bloom of krill, their primary food source in the Southern Ocean.

"They seem to know that changes happening in their immediate environment are linked to conditions thousands of kilometers away," said Professor Virginie Millien, a biologist and lead author of the study in Scientific Reports. "This allows them to fine-tune their migration, so they arrive just as their food supply peaks."

A race against a changing climate

This built-in timing mechanism has worked for thousands of years, but it is now being tested by rapid climate change. In recent years, warming ocean temperatures and shifting sea ice patterns have affected the start of the krill bloom. This means that even though whales are adjusting their migration, they may not be able to keep pace with these accelerating environmental changes.

"We don't know how long they'll be able to keep up," said Millien. "Every year since 2016 has been the warmest on record, and that pattern is speeding up. At some point, their memory-based strategy may no longer work."

The study found differences between males and females in their migration patterns. "Males tend to travel faster, taking more direct routes," Millien said. "Females, especially those with calves, take longer coastal routes, possibly to avoid predators and allow their young to rest."

Conservation implications

The findings underscore the need to protect critical migration corridors and feeding areas, the researchers said. With increased ship traffic along their coastal migration routes, whales face greater risks of collisions and habitat disruption. Co-author Hector Guzman of the Smithsonian Tropical Research Institute has been working on policy measures to reduce vessel speeds in key whale habitats.

"This research provides the data needed to inform conservation efforts," said Guzman. "It's not just about protecting whales; it's about preserving the delicate balance of marine ecosystems."