Dolphins killing porpoise
Posted 10 November 2009 - 08:09 AM
Monterey Bay researchers say dolphins are causing porpoise deaths
By Alia Wilson
Santa Cruz Sentinel
Posted: 11/06/2009 08:36:16 PM PST
Updated: 11/06/2009 08:36:18 PM PST
MOSS LANDING — For the past five years, the growing number of dead harbor porpoises washing up on California shores has been a marine mystery — 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 dolphins, which have a relatively docile reputation, have been attacking the smaller porpoises because the porpoises have been washing up on the shore 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 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 on board and then swim away.
The attack took place in the waters off Capitola.
"It was incredible to finally fit some action to our theories," said Okeanis field director Mark Cotter, 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 the why the dolphins attacked. Scientists have several theories, but none has been proven.
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. Once the females have their babies they become unavailable to mate.
Posted 10 November 2009 - 02:21 PM
My photo's on flickr
Crop the world ! (Using Canon 20D, 60mm, 100mm, 10-17mm FE, Ikelite)
Posted 20 January 2010 - 10:11 AM
I have no info available right now (because its late), but I think the university of Aberdeen also found that bottlenose dolphins were killing harbour porpoise in the Moray Firth.
You are right. Bottlenose Dolphins killing harbour porpoises has been known about for some time. It was first recorded in the Moray Firth in Scotland by Ben Wilson and Harry Ross back in 1996. Comptetion was food was considered the likley explanation at that time also.
Photography site: http://www.colinmunrophotography.com