‘Let’s stop and bite along the way’: Why it’s important to understand the migration patterns of Arctic whales

In the ocean, both natural and anthropogenic factors can cause ecosystem change. Such changes, whether sudden or gradual, can affect food webs by causing a redistribution of prey on which annual predators, such as migratory whales, depend. A redistribution of prey of this kind may not lead predators to change their migration patterns and timing, but to adjust their feeding habits.

A group of international researchers from Norway, the UK, and the US studied the feeding habits of humpback whales (Megaptera novaeangliae) in the Barents Sea, north of Norway. These whales usually spend the summer and autumn foraging in the Barents and Norwegian Seas before migrating to the West Indies and Cape Verde Islands to mate and give birth during the spring months.

The team’s work, titled “Don’t mind if I do: Arctic humpback whales respond to opportunities to find winter food before migration,” has been published Royal Society Open Science.

According to existing research, significant numbers of whales have not been seen in the northeast Atlantic since the period of trading in the region between 1881 and 1904, when forage fish were known to be abundant there.

However, during this study, the researchers recorded that each whale – which was first seen and identified during the summer in the Barents Sea – spends the winter in the north of Norway, eating Norwegian spring herring (Clupea harengus). These herring are known to have started wintering in this area — along the whale migration route — in large numbers since 2010.

The team collected biopsy and photographic evidence of humpback whales in the Barents Sea near the Svalbard Archipelago and in several fjords in northern Norway at different times between 2010 and 2019. Sea ice in winter, and between June and December, the waters of the Svalbard Archipelago are usually ice-free.

Intra-seasonal data from whale surveys conducted in the Barents Sea and northern Norway showed that during migration, some whales continued to forage in northern Norwegian fjords.

The researchers documented a preponderance of women during their winter observations in northern Norway, and estimated a higher pregnancy rate in winter than earlier in the season. From this they found that pregnant women—their pregnancy period lasts between 10 and 13 months—may be easier to continue their feeding time in the north of Norway, in order to increase their energy.

Additionally, the study notes that whales began feeding in the northern Norwegian fjord in 2010, coinciding with significant herring pressure there. According to a study in 2017 Mammalian Biologyhumpback whales were absent from the area before then, as the herring stock mostly wintered in the southern fjords.

Why is this important? The current study notes that “winter feeding on fjord-based herring is a strategy used exclusively by humpback whales in northern Norway. Our results show that this strategy is an important annual event for humpback whales, which rely on herring overwintering in these fjords.”

On a larger scale, it will be important for future studies to consider and evaluate the effect of human activities on migratory species, especially on their important food areas. Although the ban on poaching issued by the International Fisheries Commission has been in effect since 1985, M. novaeangliae is still threatened in other areas, including Cape Verde. The researchers emphasize that ecosystem management should prioritize fishing activities.