Scientists Have Discovered Two Dolphin Societies Merged in Rare Alliance

Scientists have discovered that two dolphin societies have merged together in a rare alliance.

It was already known that dolphins are capable of forming complex social societies. According to a study by Florida International University, mammals usually see other social groups as competition for resources, and this means behavior toward them is usually antagonistic.

However, researchers observed one such instance between spotted dolphins where that wasn't the case.

Their findings, published in Royal Society Open Science, suggest that antagonizing tendencies are "diminished" in this species, and "possibly other ecologically similar dolphins."

Spotted dolphins
A file photo of Atlantic spotted dolphins. Two separate groups have been observed merging. tswinner

The two groups of Atlantic spotted dolphins in the Bahamas were previously separated by 160 kilometers (99 miles) and a deep channel, "with no interaction previously observed." One group dwelled in the Bimini area, while the other resided in the White Sand Ridge (WSR) area.

Researchers observed the two groups for five years, from 2013 through 2018.

During this time, the study said that "many WSR emigrants were observed associating with Bimini dolphins."

"Given the generally closed nature of terrestrial mammal societies, these observations were surprising," the study said.

They also observed a large group of WSR dolphins physically immigrating into the Bimini area. The study said that this was "also unexpected."

Researchers then decided to study the "sex and age-specific associations" between the two groups.

"We predicted that, if associations between individuals from the two previously separate societies reflected the development of new social bonds, we would observe affiliative tactile interactions between WSR and Bimini individuals. What emerges is an unprecedented partial merger of these two previously unassociated and distant social networks of Atlantic spotted dolphins," the study said.

The study found members of "all age classes and both sexes" in mixed groups, however noticed a "strong bias toward finding immigrant males in mixed groups."

"Some association levels between males, and males and females, from different communities were as high as the highest within-community associations," it said.

Co-author of the study, Nicole Danaher-Garcia of the Department of Biological Sciences at Florida International University, told Newsweek that this was a particularly rare observation.

"It is very unusual for social mammal groups to integrate in the way these spotted dolphin groups have. When land mammal groups mix there is often a lot of aggression. The exception to that is bonobos, but even they haven't had such large groups fuse or stay together for so many years," Danaher-Garcia said.

"In that way, these spotted dolphins are particularly unique. We have seen strong social relationships forming between members of both groups including lots of time spent together in mixed groups and even some "friendly" behaviors, like pectoral fin contact, which plays a similar role for dolphins as grooming in primates."

Danaher-Garcia also said that researchers haven't yet confirmed a "strong motivation" for the dolphins merging.

"Sometimes primate groups will come together because it's safer, for example if there is a change in predation or significant habitat loss. The friendly behaviors and apparent ease of integration between the two communities suggests to us that spotted dolphins, and likely other similar species of dolphin, have diverged from the behavioral norm of aggression toward non-group members," Danaher-Garcia said.

Danaher-Garcia said these findings "open the door to more questions" about the species.

"We're also interested in long-term implications for dolphins around Bimini. We don't know if there is a carrying capacity for this area, but 50 dolphins is a huge addition to a community that has been stable for so long. Even though we didn't find evidence of any major impact to their social dynamics, we still don't know how this group fusion has impacted their distribution," Danaher-Garcia said.