Study tracks male Sperm whales over thousands of kilometers
Male sperm whales in the North Atlantic spend much of the year in Arctic waters, migrating south only for mating. For the first time, a research team has demonstrated that these migrations do not follow a fixed schedule.
For the first time, a Norwegian research team led by the Norwegian Polar Institute has tracked the migrations of male sperm whales (Physeter macrocephalus) in the North Atlantic over an extended period of time, gaining new insights into their movement patterns and reproduction.
For the study, which was published in Nature Scientific Reports on March 6, the researchers fitted 29 adult male sperm whales with satellite transmitters off the coast of northern Norway and Svalbard, marking the first time sperm whales have been tagged this far north, at 79°N.
Of the 26 whales that submitted data, 12 migrated south from their Arctic feeding grounds to the breeding grounds in the subtropical and tropical North Atlantic, while the remaining animals stayed in the north.
No fixed breeding season
One of the most remarkable findings of the study is that the migration of male sperm whales does not follow a synchronized pattern and they do not migrate during a specific season. Using satellite data, the researchers found that the migration of whales from Arctic waters to the south occurs sporadically between January and October, with no clear temporal trend.
The migration behavior of sperm whales is in stark contrast to that of humpback and fin whales. While these species follow a strict seasonal pattern—spending summers in polar waters to exploit the rich food supply and migrating to lower latitudes in winter for breeding—sperm whales do not adhere to a fixed schedule.
The research team suspects that sperm whales do not adhere to a fixed migration schedule because food is available at depth year-round in both high and low latitudes, and female whales are receptive to mating throughout the year. This allows males to time their migration based on their physical condition and energy reserves.
Fast and direct migration
All 12 sperm whales that left the Arctic waters followed a remarkably direct route south. They crossed a narrow corridor between Iceland, the Faroe Islands and the Shetland Islands before continuing their journey towards the tropical and subtropical Atlantic.
On average, the whales covered a distance of 5,500 kilometers to reach the breeding grounds south of the 45th parallel, which stretched from the waters off the Canary Islands and Cape Verde to the Caribbean and Brazil.
Their migration took an average of 40 days, with the whales covering 4.7 kilometers per hour, similar to humpback whales (5.8 km/h) and fin whales (4.7 km/h) on their migrations.
How long will they stay in the south?
The whales stayed in their breeding grounds for about 76 days. In contrast to the other whale species with synchronized, structured patterns and relatively narrowly defined breeding areas, the male sperm whales were spread over a huge area covering more than 10 million square kilometers.
They never stayed in one place for long—not even in the Azores, where sperm whales can be observed year-round—but continued their journey across the open ocean. This supports previous studies suggesting that male sperm whales move between groups of females rather than remaining with a single group for an extended period.
Only two of the whales could be tracked long enough to document their return to Arctic waters. These two whales returned to where they had been tagged.
Sperm whales might continue foraging even during migration and in their breeding grounds, as indicated by their deep dives—some reaching depths of up to 1,927 meters.
Only temporarily in warm waters
Unlike female sperm whales and juveniles, which never leave the warm waters of the low latitudes, adult males spend a large part of the year in the cold, food-rich Arctic waters.
This raises an interesting question: If food and females are available all year round in the tropics, why don’t the males stay there permanently?
According to the authors, one possible explanation is that larger males have an evolutionary advantage in competing for females. The highly productive Arctic waters may provide the ideal conditions for them to grow as large as possible, as quickly as possible.
Important findings for the whales’ conservation
Understanding the migration patterns of sperm whales is crucial for conservation and management. The study confirms that most of the breeding range of sperm whales in the Atlantic is in international waters where conservation regulations are not yet fully developed.
However, the large size of the breeding area, which extends over several marine regions, could give sperm whales a certain resilience to random events.◼️
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