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Page last updated at 16:58 GMT, Thursday, 22 July 2010 17:58 UK
Whale 'sense of smell' revealed
By Matt Walker
Editor, Earth News

Bowhead whale breathing hole (copyright Ansgar Walk)
A bowhead whale breaches to sample the air

Bowhead whales have a previously undiscovered ability to smell the air.

The finding could change our understanding of how baleen whales locate prey, as scientists suspect the bowhead whales sniff out krill swarms.

The whales' sense of smell was revealed when scientists dissected their bodies and found olfactory hardware linking the brain and nose, and functional protein receptors required to smell.

Previously, whales and dolphins were thought to lack the ability.

Details are published in the journal Marine Mammal Science.

We speculate that they are actually able to smell krill and may use this to locate their prey. Krill smells like boiled cabbage
Professor Hans Thewissen

Cetacean expert Professor Hans Thewissen of the Northeastern Ohio Universities College of Medicine and colleagues based in Japan and Alaska made the discovery while evaluating the brain size of bowhead whales.

The whales had been landed as part of the biannual Inupiat subsistence hunt along the north coast of Alaska, and Prof Thewissen's team was allowed to dissect the brain cavities, to evaluate how much of the brain casing a bowhead whale's brain actually fills.

"Upon taking a brain out, I noticed that there were olfactory tracts, which, in other mammals, connect the brain to the nose," Prof Thewissen told the BBC.

"I followed those to the nose, and noted that all the olfactory hardware is there."

Prof Thewissen examines a bowhead olfactory bulb
Prof Thewissen examines a bowhead olfactory bulb

That came as a surprise.

"At first glance, it would appear that whales would not have much use for smell, since everything they are interested in is below the water," explains Prof Thewissen.

"Olfaction is, by definition, the reception of airborne molecules."

Moreover, he says, in most cetacean species that have been investigated so far, which are mostly toothed whales such as dolphins, sperm whales and orcas (killer whales), the anatomical hardware needed for olfaction is missing, such as the nerves and receptor cells that deal with olfaction.

"Based on this most people assumed that no whale had a sense of smell."

Bowhead whales
Wild bowheads on the hunt?

Further studies though backed up the discovery that bowhead whales do indeed smell.

Bowhead whales have a relatively large, developed olfactory bulb that appears similar in structure to that in other animals with a developed sense of smell.

The researchers also found that bowheads have mostly functional olfactory receptor proteins, which toothed whales do not. These provide the biochemical infrastructure for the marine mammal to sample odours.

"It is remarkable that this animal, which appears to have very little use for olfaction, retained that sense," says Prof Thewissen.

"We speculate that they are actually able to smell krill and may use this to locate their prey. Krill smells like boiled cabbage."

Unlike most whales, bowheads have separate nostrils, which suggest they may be able to sense the direction a particular smell is coming from.

SOURCES

It might also mean that human pollution that masks ocean scents could also impact on this endangered species.

"Part of the motivation to study olfaction from the Native community's perspective was that the whale hunters have long said or 'known' that bowheads are capable of smell, so this was an obvious hypothesis to test using western science," adds co-researcher Mr Craig George of the Department of Wildlife Management in Alaska.



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