By Stephen Beech
Whales breed in specific areas deep beneath the Arctic Circle ice, reveals new research.
Scientists used state of the art AI technology to analyze the calling and singing of bowhead whales.
Their findings, published in the journal Scientific Reports, suspect that the ocean giants likely reproduce beneath the sea ice north west of Spitsbergen, Norway.
And bowheads, a species of baleen whale named after its characteristic massive triangular skull which it uses to break through Arctic ice, uses open water in the eastern Fram Strait – the waterway between Greenland and Spitsbergen – as a migration corridor.
The conclusion comes from researchers in the Ocean Acoustics Group at the Alfred Wegener Institute (AWI), Germany, who recorded bowhead whales calls using underwater hydrophones.
For the study of bowhead whale habitat use in relation to sea-ice cover, the research team analyzed the recordings using artificial intelligence (AI).
The researchers explained that if bowhead whales produce particularly varied and diverse calls in one area, it is very likely that the area is a breeding ground.
AWI researchers had previously installed hydrophones across the vast, partly ice-covered Arctic Ocean, that can continuously record underwater sounds
The hydrophones allow them to document calls of sound-producing species in remote regions without being on site and to draw conclusions about the animal’s behaviour based on the acoustic data.
Study first author Marlene Meister explained that bowheads around Spitsbergen were massively hunted during times of commercial whaling, reducing the population from an estimated 33,000 to 65,000 whales to just a few hundred.
She said that although the Spitsbergen population has been protected since the 1930s, it has not so far shown clear signs of recovery.
Meister, a doctoral student at AWI, said: “Bowhead whales are severely threatened by the decline of Arctic sea ice, as it represents an important habitat where they find abundant prey and protection from hunting orcas.
“If the ice disappears, the population will lose a central habitat.
“It is likely not possible for the whales to simply move farther north, as food availability there is very limited.”
She said the fact receding ice is making the Arctic Ocean more accessible to shipping in turn increases the risk of habitat pollution from oil and noise, as well as the risk of whales colliding with ships.
To better assess the consequences of that habitat loss, the research team focused on the occurrence and acoustic behaviour of bowhead whales in areas with different sea ice conditions.
Meister said: “Observations show that the Spitsbergen population frequently occurs in areas covered with sea ice, from the ice edge to several hundred kilometers into the pack ice, where openings in the sea ice serve as breathing holes for the whales.”
The research team investigated two contrasting regions in Fram Strait.
The first was located north-west of Spitsbergen in predominantly ice-covered water, from where acoustic recordings from 2022 and 2023 were analyzed.
The second region was located in the eastern Fram Strait in open water, where acoustic data from 2012 to 2023 was available.
The research team converted the audio data into spectrograms and evaluated them using AI.
They focused in particular on the region north-west of Spitsbergen, where singing occurred between October and April.
The researchers manually divided the recorded bowhead whale singing into individual songs, and analyzed their temporal occurrence in relation to sea ice conditions.
Twelve different songs were detected north west of Spitsbergen, each occurring over periods ranging from days to weeks.
From October onward, the number of different songs per month increased and peaked in February with eight different songs.
Meister said: “One possible explanation is that more animals were present in the region in February and produced a broader array of songs, which increased overall song diversity.
“Another possibility is that individual whales sang more diversely in February, potentially gaining a reproductive advantage if females prefer males with more diverse song repertoires.”
She says the increase in song diversity coincided with a regional retreat of sea ice at the boundary of the study region.
In December, the recorder was located up to 200 kilometers (125miles) inside the sea ice , whereas in February, after the ice had receded, it was situated directly at the ice edge.
Meister said: “The close link between song diversity and distance from the ice edge was a surprising result for us.”
But, in the second, ice-free region only calls and no songs were detected.
Meister said: “Bowhead whales were regularly present in the ice-free eastern Fram Strait, but the reason for their presence there remains unclear.”
She added: “It is possible that the animals are merely passing through the area and call to maintain contact with each other.
“The fact that we did not detect any songs there also suggests that the eastern Fram Strait is not a breeding ground.”
She says the study contributes to a better understanding of bowhead migration patterns and helps to identify key habitats – such as feeding and breeding grounds – so that conservation measures can be as effective as possible.
