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| Pic: Dolphin Research Institute |
Dolphin Research
InstituteUS researchers may have finally proved what many have
long suspected - that dolphins are capable of stunning their prey
using a blast of sound.
This week's
New Scientist reports that Ken Marten of Earthtrust in Hawaii
and Denise Herzing from Florida Atlantic University now have hard
proof of this theory that has been around for almost twenty years.
In work submitted
to The Journal of Aquatic Mammals, Marten and Herzing claim to
have hard evidence of the behaviour captured acoustically and
visually on videotape.
"It's
the first time anyone's got shots like this," Marten says.
Marten had
noticed before that dolphins close to herring would emit low bangs
at the frequency the fish hear best at, and had suggested the
bangs were designed to damage the fish's hearing apparatus. He
has now taped a dolphin emitting a sequence of low- frequency
"bangs" while chasing a fish.
In a further
experiment, Marten showed that low sounds with similar acoustic
properties to dolphins' clicks disorientated anchovies to the
point where they swam in circles, remained still or died. "It
could also mess up their schooling," he says.
Meanwhile,
Herzing has found evidence of a different strategy. She recorded
wild Atlantic spotted dolphins emitting a medium-frequency buzz
while searching for prey in sand on the seabed. She says buried
eels jumped out of the sand, and either stopped completely or
moved sluggishly as if they were stunned, giving the dolphin time
to catch them.
"Dolphin
sonar is more complex than any man made technology," Wendy
Dunn of the Dolphin Research Unit told ABC Science Online. "What
this is all about is understanding the properties of dolphin sonar
and what is capable of doing."
"If the
researchers have actually been able to combine an acoustic recording
with a visual recording, and been able to use artificially produced
dolphin clicks to stun anchovies, then that will be a first."
"This
sort of thing has been suspected for so long. To actually get
some confirmation of this would be really exciting," she
says.
Other researchers
remain unconvinced, says New Scientist. "If they can prove
it, I'd hate to be negative," says Pete Tyack from the Woods
Hole Oceanographic Institution near Boston. But Tyack thinks the
dolphins may be using sound merely to locate their prey, not to
stun it. "The underwater world is unfamiliar to us and you
have to be careful with interpretations," he says.
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