Dolphins are highly social creatures, known for forming complex and long-lasting relationships with one another—and, sometimes, with other species. But dolphins can be quite choosy when it comes to picking their buddies. As the New Scientist reports, a study of bottlenose dolphins in the northern Adriatic has found that the animals not only form distinct friend groups, but also shun members of rival “cliques.”
It is often said that dolphins are “fission-fusion” species, meaning that they merge and split in a malleable social structure. But according to the authors of the study, published recently in the journal Marine Biology, dolphin societies can vary greatly from population to population. Dolphins in Florida, for instance, seem to segregate based on sex and age. Among the dolphins of Doubtful Sound, New Zealand, strong bonds form between the sexes. And based on nine years of observations, the researchers behind the new study conclude that dolphins that frolic in the Adriatic’s Gulf of Trieste, near the coast of Slovenia, have quite stable social structures.
Dolphins in this region have divided into two main groups, comprised of both males and females that form long-lasting social bonds. The distinct clusters have “core” members, with other dolphins in the group forming social “tiers,” as the researchers put it. There was also a third, smaller cluster of dolphins, which had “no particularly strong bonds with anyone,” the study authors write. These lonely dolphins seemed to act as “social brokers” between the two main groups, preventing them from becoming completely isolated from one another. But the main groups seldom interacted; Tilen Genov, a marine biologist with the Morigenos-Slovenian Mammal Society, tells Atlas Obscura’s Anna Kusmer that the groups have only been observed together four times over the past 16 years.
In their efforts to avoid one another, the clusters seem to have come up with a system for sharing desirable parts of the sea. One group predominantly fed in the core study area in the morning hours, while the other would appear in the evening. Similar patterns of segregation have been seen among bottlenose dolphins in Scotland, where different groups take turns occupying an inlet called Moray Firth. But in that case, the exchange seems to be seasonal, with the swap occurring in the summer. The Adriatic dolphins were sharing their favorite patch of sea every day.
“We were quite surprised by this,” Genov says. “It is not uncommon for dolphins to segregate into different parts of the sea, but to have certain times of the day in which they gather is unusual.”
It is not clear why the Adriatic dolphins avoid feeding together. It is possible that they are trying to avoid aggressive interactions between the groups, or perhaps they simply have varied foraging preferences. Genov and his colleagues did observe that the clusters interacted differently with fishing trawlers: One group trailed after the boats to scoop up loose fish, and the other did not.
“[N]ot all population segments necessarily respond to, or interact with, human activities the same way, or at the same time,” the study authors point out. It is therefore important for scientists to understand the intricacies of dolphin societies—like how they splinter off into different groups with distinct hunting strategies—so they can better plan to conserve and manage the animals.