The dolphins had lived in two distinct groups, with one foraging on fish discarded by trawlers while the other hunted in the wild.
But a ban on the fishing boats in key areas has brought the two groups together to hunt once again.
Writing in the journal Animal Behavior, lead author Ina Ansmann of the University of Queensland, says the dolphins have basically rearranged their entire social system since the fishing trawlers disappeared.
Dolphins are known to live in what is called a fission-fusion society, meaning they gather in groups, then split up to form different groups.
The Moreton Bay dolphins were the only known example of a single population of two groups that didn’t associate with each other.
Photos: Ina Ansmann