Divided dolphin societies merge ‘for first time’

A unique social division among a population of bottlenose dolphins in Australia’s Moreton Bay has ended, according to a new study.

The dolphins lived as two distinct groups that rarely interacted, one of which foraged on trawler bycatch.

But scientists think that a ban on fishing boats from key areas has brought the two groups together.

They believe these socially flexible mammals have united to hunt for new food sources together.

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”.

But since the study that discovered the rift, trawlers have been banned from designated areas of the bay leading to a 50% 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 changes gave scientists a unique opportunity to observe the adaptability of dolphin society.

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 Dr Ina Ansmann, marine vertebrate ecologist, University of Queensland, and the study’s lead author.

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,” Dr Ansmann told BBC Nature.

Full story: BBC

More from this site

Bottlenose dolphins have large brains and quickly learn new behaviours. Using a wide range of sounds to communicate with other members of the group, or “pod”, they have been observed showing remarkable individual and social intelligence:

  • One for the team: watch how a single dolphin peels off from the pod to shepherd the mullet into the open mouths of the group
  • Bubble trouble: initially cautious of the new shapes created by the bubble machine, you can see how quickly the inquisitive dolphins turn this experiment into a game
  • Mirror, mirror on the wall: from the reaction of these dolphins to their own reflection, scientists believe the animals have a developed sense of self
  • Thinking out cloud: see how these dolphins off the Florida coast have developed a unique hunting strategy for the shallows off the Florida coast

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