New tool use by dolphins

Already famed as Earth’s first tool-using marine mammals, the bottlenose dolphins of Australia’s Shark Bay have proved handy yet again, by using conch shells to trap tasty fish, then shaking them into their mouths like sardines from a tin.

Unlike sponging, however, in which dolphins use sponges to find fishes hiding in mud, conching isn’t yet widespread in Shark Bay. It appears to be a relatively new innovation, pioneered by a few individuals and finally catching on.

“The extent to which the conch shell is manipulated and the rarity of the behavior suggest that ‘conching’ takes some skill and practice and might thus be another rare individual foraging tactic in Shark Bay,” wrote biologists led by the University of Zurich’s Michael Krutzen in Marine Mammal Science.

While that study came out in April, an Aug. 24 press release from Australia’s Murdoch University, home of co-authors Simon Allen and Lars Bejder, reported that conching has been observed at least six times in the last four months. That’s as often as conching was seen between the first sighting in December 1996 and the afternoon of July 31, 2007, when during a survey of western Shark Bay the researchers spotted an unfamiliar dolphin.

As they lingered nearby, hoping to dart a biopsy sample from her skin, the dolphin dived and then surfaced with her beak lodged in a conch shell, which she waved back and forth above the water. She dove again. Before she surfaced, four more dolphins arrived. When she returned with the conch, they were waiting and watching. So were the researchers.

“Photographs were taken, with two of these clearly revealing the posterior portion of a fish protruding from the conch aperture and held in the dolphin’s jaws,” they wrote in Marine Mammal Science. “The dolphin lifted the conch out of the water and manipulated it in such a manner as to drain the water and the fish from the shell.” It appeared to be an emperor fish.

Until the researchers photographed Con — sort for “Concher,” as they code-named the dolphin — the purpose of conch-wielding was unknown. From their handful of fleeting glimpses over the years, the researchers thought it likely that dolphins were simply eating conch snails inside their shells, or perhaps showing off, as do stick-wielding, clay-throwing dolphins in the Amazon.

Almost two years later, in April 2009, the researchers saw another conching dolphin, this time in a shallow, seagrass-covered spot where a wildlife observer had seen dolphins digging through seabed with shells of baler, another large marine mollusk.

Exactly how the shells are used underwater isn’t yet known. Fish might swim into them while being chased, unwittingly turning themselves into packaged snacks. The dolphins could also use the shells like nets or containers, a possibility suggested by the wildlife observer’s report of seabed-digging.

Also unknown is how conching emerged: as a variation on sponging, perhaps, or in flashes of insight from creatures whose intelligence may rival our own but happen to lack fingers and hands. Because Shark Bay’s dolphins are very territorial, however, and conching has been witnessed in disparate locations on its east and west sides, the researchers believe conching was discovered several times independently.

If, as with sponging, conching is taught primarily by females to other females, then conching was likely an invention of single mothers trying to feed their families. That it’s being witnessed with more frequency suggests Shark Bay’s dolphins are learning about it. Perhaps those four who watched Con were taking a lesson.

So far, only one male dolphin, the individual spotted in 2009, has been seen conching. While his name among dolphins is unknown, the researchers dubbed him Wim, short for William the Concherer.

Source: Wired