The left panel illustrates the Svalbard Archipelago, with black dots marking GPS locations where photographic records of humpback whales (Megaptera novaeangliae) were captured near Kong Karls Land. The inset highlights the primary locations (Andøya, Kvaløya, and Kvænangen fjord) within the northern Norwegian foraging area. Credit: Royal Society Open Science (2023). DOI: 10.1098/rsos.230069
In the world’s oceans, both natural forces and human activities can trigger significant ecosystem transformations. These alterations, whether sudden or gradual, can disrupt the food web, leading to changes in prey distribution, which can, in turn, impact seasonal predators like migratory whales. Such prey redistribution not only prompts shifts in migration routes and timing for these predators but also necessitates adjustments in their foraging behaviors.
An international research team comprised of scientists from Norway, the United Kingdom, and the United States has conducted an extensive study on the foraging habits of humpback whales (Megaptera novaeangliae) in the Barents Sea, situated north of northern Norway. Traditionally, these whales spend the summer and autumn months foraging in the Barents and Norwegian Seas before embarking on their spring migration to the West Indies and Cape Verde Islands for mating and breeding.
The team’s research, titled “Embracing Opportunities: Arctic Humpback Whales Respond to Winter Foraging,” has been published in the journal Royal Society Open Science.
Historically, significant numbers of humpback whales had not been observed in the northeastern Atlantic since the era of commercial whaling in the region, spanning from 1881 to 1904 when abundant forage fish populations were recorded. However, during this study, the researchers documented individual whales initially sighted and identified during the summer in the Barents Sea, now spending their winters in northern Norway, where they forage on Norwegian spring-spawning herring (Clupea harengus). Remarkably, these herring have also begun overwintering in the same area, aligning with the whales’ migration route, in substantial numbers since 2010.
The team collected biopsy samples and photographic evidence of humpback whales in the Barents Sea near the Svalbard Archipelago and various fjords in northern Norway between 2010 and 2019. Due to the relatively warmer waters of the North Atlantic, northern Norway remains free of sea ice during the winter, while the waters around the Svalbard Archipelago typically become ice-free from June to December.
Data comparisons within a single season of whale observations in the Barents Sea and northern Norway revealed that some of the whales continued foraging in the northern Norwegian fjords during their migration. Intriguingly, the researchers noted a prevalence of females during their winter observations in northern Norway, estimating a higher pregnancy rate in winter compared to earlier in the season. This suggests that pregnant females, with a gestation period spanning 10 to 13 months, might be particularly inclined to extend their foraging season in northern Norway to optimize their energy reserves.
Furthermore, the study highlights that the whales began feeding in the northern Norwegian fjord area in 2010, coinciding with the notable presence of herring in that region. Before this, as indicated by a 2017 study in Mammalian Biology, humpback whales were absent from the area since this particular herring stock typically overwintered in fjords farther to the south.
The significance of this discovery lies in the observation that “winter foraging on fjord-based herring is a strategy predominantly employed by female humpback whales in northern Norway. Our findings imply that this strategy has become a crucial annual event for humpback whales, contingent upon the overwintering of herring in these fjords.”
On a broader scale, future research should consider and evaluate the impact of human-driven factors on migratory species, particularly in their critical feeding grounds. Despite a commercial whaling moratorium enacted by the International Whaling Commission in 1985, humpback whales (M. novaeangliae) remain endangered in certain regions, including Cape Verde. The researchers emphasize that ecosystem management should prioritize activities such as shipping and fishing to safeguard these species.
More information:
Lisa Elena Kettemer et al, Embracing Opportunities: Arctic Humpback Whales Respond to Winter Foraging, Royal Society Open Science (2023). DOI: 10.1098/rsos.230069
Journal information: Royal Society Open Science, Mammalian Biology