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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.
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"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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