Rare divided dolphin groups unite for first time

Last Updated: Monday, July 30, 2012 - 18:17

London: A unique social division among two groups of bottlenose dolphins that rarely interacted has finally ended at Australia`s Moreton Bay, after they re-arranged their whole social system, a new study has found.
The dolphins lived as two distinct groups, one of which foraged on trawler bycatch.

Scientists believe that a ban on fishing boats from key areas has brought the two groups together, adding, these socially flexible mammals have united to hunt for new food sources together, the `BBC News` reported.

The findings are published in the journal Animal Behaviour.

The Moreton Bay dolphins were thought to be the only recorded example of a single population that consisted of groups that were not associating with each other in a split dubbed "the parting of the pods".

Since the study that discovered the rift, trawlers have been banned from designated areas of the bay leading to a 50 per cent reduction in the fishing effort.

A key area of the bay to the south, where the social split was observed by the previous study, has been protected.

The "trawler" dolphins from Moreton Bay had previously fed on the bycatch from boats while the "non-trawlers" found other sources of food.

"There`s never been really any experiments looking at social structure... Where you can compare what it was like before and what it is like now," said study leader author, Dr Ina Ansmann, marine vertebrate ecologist, University of Queensland.

Analysing how the population interacted before and after trawling meant the team could assess how the dolphins` social network had changed.

"The dolphins had basically re-arranged their whole social system after trawling disappeared so they`re now actually interacting again," Ansmann told BBC Nature.

"Presumably they`re sharing information, co-operating and things like that," said Ansmann.

Dolphins operate in what is called a fission-fusion society, forming groups and then splitting up to form different groups.

PTI



First Published: Monday, July 30, 2012 - 18:17

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