29 July 2009

Bowhead whale: The nightingale of the ocean

It is now generally accepted that the bowhead whale is the longest lived mammal on the planet, with a lifespan of over 200 years. But that it can sing with "more than one voice" and that it changes its repertoire from year to year is news. This behaviour is unique among baleen whales and is a newly discovered phenomenon that has been investigated by researchers at the University of Copenhagen.

The return of the bowhead whale

The project comes at a time when the bowhead whale, after many years of absence, has returned to the waters around northwest Greenland, including Disko Bay. It wasn't that many years ago that the bowhead whale was written off as extinct in the waters around Greenland and especially in Disko Bay in northwest Greenland where University of Copenhagen has its Arctic Field Station.

But now the situation has changed and adult bowhead whales, which can grow up to 18 metres long and weigh 100 tons, have returned to the bay. Probably because global warming has opened up the Northwest Passage, making it ice free at certain times of the year for the first time in 125,000 years. This gives bowhead whales from the northern Pacific a chance to reach Disko Bay and mate with the small local population. There is now believed to be around 1200 whales in the waters around Disko Island.

Sophisticated whale songs

Hydrophones have revealed that the whales have developed very sophisticated songs that are used to attract a mate and thereby ensure the species' survival.

"Whale song is not a new phenomenon. But the special thing about the bowhead whale's song is that they sometimes sing with 'more than one voice'. They produce two different songs or sounds, which are then mixed together. This has not been seen in other baleen whales. It turns out that bowhead whales change their songs from year to year and never repeat songs from previous years. I.e. the whales have a new repertoire each year – presumably as part of the eternal struggle to obtain a mate,” said Outi Maria Tervo, a PhD student at the University of Copenhagen and the current scientific leader of the Arctic Station in the town of Qeqertarsuaq (Godhavn) on Disko Island.

"The bowhead whale is in the same weight class as fin whales and blue whales but they produce much more complicated songs, at higher frequencies, between 100 and 2000 hertz – cycles per second. At the same time the question arises whether the changes in their song repertoire are due to bowhead whales being so sophisticated that they change their songs from year to year in order to constantly attract and mate with new partners and thereby spread their genes. The bowhead whale is the only species of 'singing' whale where the gender of the singers has not yet been established," says Outi Maria Tervo, who now has a serious opportunity to study bowhead whales via different types of hydrophones, thanks to donations from, amongst others, the A.P. Møller fund.

Her studies of the love songs of bowhead whales have just been chosen to be presented at large international conference on marine mammals later this year in Canada. At the same time the A.P. Møller fund has chosen to support the project with 1.8 million Danish kroner over a three year period.

Godhavn and the bowhead whales

Professor and Science Director of Natural History Museum, University of Copenhagen and Director of University of Copenhagen's Arctic Station in Greenland, Reinhardt Møbjerg Kristensen, explains that Godhavn with its natural harbour is inextricably connected with the giant bowhead whale, which is also part of the town’s crest.

Godhavn was founded in 1773 and became a base for whalers from all over Europe. Wale oil was obtained from the blubber of the whales, and was used for street lightning in almost all European cities, amongst other things.

In the 1890's the whale adventure was almost over. Stocks had almost disappeared. During a 200 year period over 30,000 bowhead whales had been killed. Bowhead whales were not protected until 1938 in Greenland. However in the 1970's when Reinhardt Møbjerg Kristensen was scientific leader of the Arctic Station, he informed the Greenland Fishery Board that the stocks were at an all time low.

World oldest mammal

As for the age of bowhead whales, it was, for many years, difficult to definitively establish the species as the "world's oldest mammal" as they have baleen instead of teeth. In connection with the 200th anniversary of Godhavn's founding a whale was caught that was older than the town itself. The Greenlanders didn't know that though, even though there were lots of old wives tales about old Norwegian harpoons being found in some of the whales that were caught. The mystery increased because at the same time ancient harpoons from a long since vanished Inuit culture were found in bowhead whales. An investigation of a whale caught off the coast of Alaska showed that it was 213 years old. A reliable method of dating whales that is available today is to measure the amino acid half life in their eyes (the so-called "aspartic acid racemization dating" method).