Listening to Greenland's bowhead whales

Posted by: Outi Tervo, marine biologist 

Bowhead swimming in the distance amidst ice.

The bowhead acoustic work we’ve been doing is very exciting. This is the first time acoustic data has been collected in this region during the whales’ northward migration. That data will help marine biologists gain a better understanding of these remarkable creatures.

The bowhead whales we have seen and heard off the West Greenland coast belong to the Davis Strait – Baffin Bay population numbering about 4000, the second largest population after those found in the Bering Sea and Beaufort Sea. The whales leave their winter and spring aggregation area in Disko Bay in late May and early June and head north along the coast of Greenland and finally cross over Baffin Bay towards Lancaster Sound. By the time the whales leave the Disko Bay area, they have more or less stopped singing after a very active singing period from February to mid April.

Bowhead whales have an extensive acoustic repertoire and vocalize throughout most of the year. Bowhead whale acoustic signals can be divided into simple frequency modulated (FM) calls, complex amplitude modulated (AM) calls and songs. Simple FM calls are short, narrowband tonal calls often referred to as moans. Complex AM calls are broader band signals with pulsive components incorporated into a tonal part giving these signals a harsher and coarser sound. Whale songs, like the songs of birds, are defined as a series of stereotyped tonal song notes repeated in a pattern. All these vocal signals are thought to function for communication. Songs have also thought to have significance in bowhead whales’ breeding behaviour and mate choices.

The bowhead whale sounds we have recorded so far have been simple FM and complex AM calls. Due to the low frequencies of these signals, they attenuate (lose intensity) very little in water and therefore have the potential for long range communication. These calls could probably enable individual whales that are more than 100 kilometres apart to stay in contact with each other and maintain group cohesion during migration. Some data also indicates that bowhead whales can use the echoes of their own vocalizations for discriminating between different types of ice. It could be that the low frequency moans of bowhead whales that we have heard are helping the whales find their way in the underwater maze of ice.

The bowhead whale is a large baleen whale species with a circumpolar distribution in the Arctic. They reach an average length of 18 metres when full grown and can weigh up to 80 tons. Bowhead whales do not possess any teeth but instead use their numerous baleen plates to filter microscopic crustaceans from the water. They have the longest and most numerous baleen plates of baleen whales. Bowhead whales are highly adapted to their ice-filled environment. They can break through up to 60-centimetres of ice, have the thickest insulating blubber layer of any whales and, like belugas and narwhals, lack a dorsal fin that could be damaged when scratching against sea ice. Bowhead whales can reach an age of more than 100 years making them one of the longest-lived animals on earth.

Photos: Chris Debicki