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Friday, 8 June
2007
Researchers in
Key Largo, Florida have audio and spectrographic evidence
of a dolphin stunning and disabling her prey with sound.
This topic, commonly referred to as The Dolphin Big Bang,
has been a hotly debated issue for many years with experts
on both sides of the fence.
This week Jack
Kassewitz of SpeakDolphin.com has announced he has
photographed and recorded a dolphin named Castaway,
actively targeting and stunning a mullet fish. Days later,
two researchers from the Marine Mammal Conservancy (MMC)
were carefully monitoring Castaway when they witnessed her
emitting a powerful blast of sound in the direction of
another mullet. That fish showed immediate signs of
distress and disorientation. Stacey Anderson, one of the
MMC researchers who witnessed the event said "Castaway
yelled very loudly at a mullet, the mullet seemed unable
to move at first, and then the mullet started swimming on
its left side with its head partially out of the water and
gulping air. Thirty minutes later, the fish appeared near
death when we removed it from the dolphin's pen."
Each acoustic
event was recorded using high-definition hydrophones in
the water, with the data stored digitally onto hard disk
recorders. Kassewitz was underwater filming Castaway when
the first event took place. He said, "I noticed her sounds
and a mullet rapidly retreating from her during the
filming, but I didn't realize what had happened until
later when we compared the recorded acoustic signals to
the second event, in which the fish was clearly disabled
and likely died."
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The SpeakDolphin.com team is part of a multi-disciplinary
research project with MMC and Dolphins Plus assisting
Castaway, a stranded, deaf, pregnant offshore bottlenose
dolphin (Tursiops truncatus). This pregnant female
stranded on November 11, 2006 at Castaway Cove in Vero
Beach, |
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Florida
and spent 79 days in rehabilitation at Mote Marine
Laboratory, recovering enough to be approved for
release. An attempt to release her was made on January
30th, 2007. After 3 unsuccessful attempts, including one
release into the middle of a pod of dolphins 3+ miles
offshore, she was sent to the MMC facility in Key Largo,
Florida, for further evaluation and rehabilitation. |
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Spectrogram of dolphin-emitted stun sequence. |
"These unique
recordings of video and sound have come about because we
are monitoring Castaway 24 hours a day, seven days a week
for a period of 7-9 months. It seems ironic that a deaf
dolphin would teach us so much about this debated topic of
whether Dolphins can stun prey," Kassewitz added. In 2006,
the Journal of the Acoustic Society of America, contained
a research paper by Kelly J. Benoit-Bird, Whitlow W. Au,
Ronald Kastelein that concluded, "Based on the(ir)
results, the hypothesis that acoustic signals of
odotocetes alone can disorient or "stun" prey cannot be
supported (emphasis added)."
The recent
discovery with Castaway in Key Largo refutes that paper.
Kassewitz said in response, "I am sorry that their
research has been overturned, but we now know that
dolphins can indeed stun their prey."
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