Semi-aquatic mammals show underwater smell tracking traits

Contrary to long held beliefs, U.S. researchers have found evidence that shows moles and shrews can reach out for their underwater prey through their unique bubble sniffing behavior.

Though, it has long been known that aquatic animals have a sense of smell, what wasn't clear, however, was the technique used by semi-aquatic mammals to hunt their prey underwater.

Kenneth Catania, a neurobiologist at Vanderbilt University in Nashville, Tennessee, the author and lead researcher of the study aptly felt, "If you go through the literature on the historical ideas of olfaction, there's a lot of statements to the effect that 'Obviously, it's impossible for a mammal to smell underwater'."

Various land mammals like, whales and dolphins had shown degenerated olfactory features during their transition and adaptability to aquatic life. Also, semi-aquatic mammals were thought to use their olfactory capabilities only on land.

Catania had been tracking activities of star-nosed moles for a long time when he decided to follow them underwater too.

To capture their underwater eating habits, Catania set up a high-speed video camera under a glass-bottomed aquarium along with a star-nosed mole and an earthworm as its prey.

Catania noticed that when the moles are underwater, they repeatedly blew out bubbles from their nostrils, only to quickly suck them back in.

During each puff, nearly a dozen bubbles were produced each second, of which most bubbles never detached the nose. The frequency and volume of the bubbles was strikingly similar to the sniffing behavior that rats and mice used to track their prey on land, revealed Catania.

To check, he laid down an underwater earthworm scent trail. Nearly 75-100 percent of the times the moles tracked down the earthworm using the bubble sniffing behavior, proving that the bubbles allowed the mixing of odor molecules in the water with that of air and back into the nose. This helped them smell their prey and reach out for it.

However, when a fine-meshed grid was placed between the scent trail and the mole, stopping bubbles from reaching the smelly molecules, the mole's ability to track dropped to 50 percent, reported Catania.