yesawaken
07-11-2009, 03:30:AM
Video shows dolphins attacking porpoise in Monterey Bay
http://extras.mnginteractive.com/live/media/site570/2009/1106/20091106__a5.dolphins.1106~1_GALLERY.jpg
By ALIA WILSON
MediaNews
Updated: 11/06/2009 01:29:38 AM PST
For the past five years, the growing number of dead harbor porpoises washing up on California shores has puzzled biologists — until now.
In September, marine biologists with Okeanis, a nonprofit conservation group based in Moss Landing, captured the only video footage taken in Monterey Bay of bottlenose dolphins attacking and killing a porpoise.
Scientists suspected the dolphins, which have a relatively docile reputation, have been attacking the smaller porpoises because porpoises have been washing ashore with rake marks and internal bleeding, but they never had any proof.
"Now, we know the how, but we still are unsure of the why," said Daniela Maldini, president of the Okeanis board. "We have been observing the social structure of these animals and it has taken us 20 years to do that. This type of behavior is something new."
Maldini has been monitoring the same group of about 600 dolphins since 1990. Maldini said Okeanis believes in collecting a variety of data before problems arise to better diagnose critical changes in the environment. But what they captured raises more questions than supplies answers.
The video shows a group of male dolphins using several techniques to assault a porpoise as it tries desperately to get away. The dolphins corral the porpoise, ram it with their beaks, scrape or rake it with their teeth and drown the porpoise by jumping on top of it. The dolphins then bring the carcass up to the Okeanis researchers, watch them bring it aboard and then swim away.
The attack took place off New Brighton Cove.
"It was incredible to finally fit some action to our theories," said Mark Cotter, Okeanis field director, who captured the footage along with fellow researcher Thomas Jefferson. "It diminishes the image of the bottlenose dolphin in a way that wild animals are not like those you see at SeaWorld. They all have their own individual personalities."
Cotter said the next step is to figure out why the dolphins attacked. Scientists share several theories, but none have been proved.
Maldini said there have been documented cases of male dolphins killing infants in the United Kingdom because their were few females available to mate with. After the females have their babies, they become unavailable to mate.
"Harbor porpoises are the same size as baby bottlenoses. No bottlenose babies are washing up onshore though, just porpoises," Maldini said. "It would be weird to think they are doing it out of competition for food because sea lions are a more likely candidate for those attacks. We're on the fence."
A collaborative effort involving Okeanis, the Santa Barbara Museum of Natural History, the Marine Mammal Center and the Moss Landing Marine Mammal Center has been looking into the possible reasons why and are working on publishing two papers at the beginning of the year about their findings.
Last year, there were about 74 porpoise strandings statewide, said Michelle Berman, the assistant curator at the Santa Barbara Museum of Natural History.
"Historically, the strandings have been due to fishery interactions but with these strandings there were no external indications right away," Berman said. "With most of these porpoises, the injuries were internal. Several had broken ribs, one had a fractured skull that had punctured the brain. But once I could see the toothmarks on others, I knew right away that it had to be a bottlenose dolphin."
Berman said she began seeing the strandings in 2004. Typically, her region sees one to two a year, but last year they had 16.
"We have just been calling it phocoenacide, because it doesn't involve just one type of harbor porpoise. We've had adult males, females and even older males too," Berman said. "It's frustrating for us to know what went on but not know why or where so having a group like Okeanis collecting this type of data, out in the ocean, is huge for us."
http://www.montereyherald.com/local/ci_13727971
http://extras.mnginteractive.com/live/media/site570/2009/1106/20091106__a5.dolphins.1106~1_GALLERY.jpg
By ALIA WILSON
MediaNews
Updated: 11/06/2009 01:29:38 AM PST
For the past five years, the growing number of dead harbor porpoises washing up on California shores has puzzled biologists — until now.
In September, marine biologists with Okeanis, a nonprofit conservation group based in Moss Landing, captured the only video footage taken in Monterey Bay of bottlenose dolphins attacking and killing a porpoise.
Scientists suspected the dolphins, which have a relatively docile reputation, have been attacking the smaller porpoises because porpoises have been washing ashore with rake marks and internal bleeding, but they never had any proof.
"Now, we know the how, but we still are unsure of the why," said Daniela Maldini, president of the Okeanis board. "We have been observing the social structure of these animals and it has taken us 20 years to do that. This type of behavior is something new."
Maldini has been monitoring the same group of about 600 dolphins since 1990. Maldini said Okeanis believes in collecting a variety of data before problems arise to better diagnose critical changes in the environment. But what they captured raises more questions than supplies answers.
The video shows a group of male dolphins using several techniques to assault a porpoise as it tries desperately to get away. The dolphins corral the porpoise, ram it with their beaks, scrape or rake it with their teeth and drown the porpoise by jumping on top of it. The dolphins then bring the carcass up to the Okeanis researchers, watch them bring it aboard and then swim away.
The attack took place off New Brighton Cove.
"It was incredible to finally fit some action to our theories," said Mark Cotter, Okeanis field director, who captured the footage along with fellow researcher Thomas Jefferson. "It diminishes the image of the bottlenose dolphin in a way that wild animals are not like those you see at SeaWorld. They all have their own individual personalities."
Cotter said the next step is to figure out why the dolphins attacked. Scientists share several theories, but none have been proved.
Maldini said there have been documented cases of male dolphins killing infants in the United Kingdom because their were few females available to mate with. After the females have their babies, they become unavailable to mate.
"Harbor porpoises are the same size as baby bottlenoses. No bottlenose babies are washing up onshore though, just porpoises," Maldini said. "It would be weird to think they are doing it out of competition for food because sea lions are a more likely candidate for those attacks. We're on the fence."
A collaborative effort involving Okeanis, the Santa Barbara Museum of Natural History, the Marine Mammal Center and the Moss Landing Marine Mammal Center has been looking into the possible reasons why and are working on publishing two papers at the beginning of the year about their findings.
Last year, there were about 74 porpoise strandings statewide, said Michelle Berman, the assistant curator at the Santa Barbara Museum of Natural History.
"Historically, the strandings have been due to fishery interactions but with these strandings there were no external indications right away," Berman said. "With most of these porpoises, the injuries were internal. Several had broken ribs, one had a fractured skull that had punctured the brain. But once I could see the toothmarks on others, I knew right away that it had to be a bottlenose dolphin."
Berman said she began seeing the strandings in 2004. Typically, her region sees one to two a year, but last year they had 16.
"We have just been calling it phocoenacide, because it doesn't involve just one type of harbor porpoise. We've had adult males, females and even older males too," Berman said. "It's frustrating for us to know what went on but not know why or where so having a group like Okeanis collecting this type of data, out in the ocean, is huge for us."
http://www.montereyherald.com/local/ci_13727971