This is the first time that a group of dolphins has been recorded trying to help or save another dying dolphin.
Korean-based scientists witnessed the event in the East Sea off the coast of Ulsan, in South Korea.
Five individual dolphins formed a raft with their bodies in an attempt to keep the stricken dolphin afloat.
Details of the behaviour are reported in the journal Marine Mammal Science.
Healthy cetaceans, the group of animals that includes whales and dolphins, have been seen attempting to provide supportive care to individuals before.
For example, in the mid-20th Century, a bottlenose dolphin (Tursiops truncatus) in captivity was seen lifting her stillborn calf to the surface with her back.
Wild bottlenose dolphins have also been seen supporting dead or stillborn calves near the surface, while some have been recorded stimulating their babies by biting them.
But all previous examples involved just one or two adult dolphins trying to rescue a calf.
Now Kyum J Park of the Cetacean Research Institute in Ulsan, Korea, and colleagues report an incident when up to 10 long-beaked common dolphins (Delphinus capensis) tried to save the life of another adult.
The researchers routinely monitor cetaceans off the South Korean coast.
During one survey, they encountered a group of long-beaked common dolphins containing more that 400 individuals being followed by approximately 500 streaked shearwaters.
Both dolphins and birds were foraging, and the research vessel approached and observed the pod several times.
A small group of dolphins had separated from the pod and were splashing near to the boat.
Closer observation revealed at least 12 individuals swimming very slowly.
Among them, one dolphin was wriggling about, its body leaning over, with its abdomen showing to the surface.
Though it could move and splash its tail, its flippers appeared to be paralysed and it had red marks on its belly.
A number of dolphins circled this group, while those within appeared to be trying to help the stricken dolphin maintain its balance, by pushing it from the side and below.
Then the 10 remaining dolphins took turns to form a raft using their bodies.
Five dolphins at a time lined up horizontally into a raft-like formation, maintaining it while the stricken dolphin moved on top and rode on their backs.
One of the dolphins in the raft even flipped over its body to better support the ailing dolphin above, while another used its beak to try to keep the dying dolphin’s head up.
A few minutes later the stricken dolphin appeared to die, its body hanging vertically in the water, with its head above the surface. It wasn’t breathing.
Five of its associates continued to interact with the dead dolphin’s body, rubbing and touching it, or swimming underneath, releasing bubbles onto it.
They carried on this way despite the dead dolphin’s body showing signs of rigor mortis, say the researchers.
Source: BBC Nature by Matt Walker