It all starts with fishermen wading into the water, until they’re about waist deep, and waiting in a line. At the signal, they cast their nets into the surf and reel in a bumper crop of mullet. But that signal is not issued by another human, instead, it's given by a dolphin. It now turns out that these famous cetaceans of Laguna, Brazil, have their own distinctive accent.
This unique relationship between fisherman and dolphin has been going on for at least 120 years. The dolphins are wild and free to do as they please, but it seems that they want to help the men catch their daily fish.
The marine mammals swim towards the beach, corralling mullet as they go. The water is so murky that the fishermen have no way of knowing where the fish actually are and are thus completely reliant on the dolphins. The animals give a signal indicating the precise moment the fishermen should cast their nets by slapping their tails or making a deep dive. Research published in the journal Ethology now shows that these dolphins “speak” in a different way from other, less helpful cetaceans.
It is thought that the collaboration benefits not only the fishermen, who on average collect bigger fish, but also the dolphins, as they get an easy picking of the fish trying to escape the nets. Yet not all dolphins that live off of Laguna engage in this cooperative behavior, so researchers wanted to see if they could pinpoint any differences between those that do help humans out, and those that don't.
To their surprise, the scientists found that the dolphins that helped the fishermen out vocalized in a different way to those that didn't, even when foraging on their own or away from humans. While it has already been shown that cetaceans from different parts of the ocean have contrasting accents, there has been little to suggest that dolphins living in the same population communicate differently.
The fact that the dolphins still have unique accents when fishing on their own suggests that their vocalizations are not directly linked to the cooperative behavior. Instead, the researchers suggest that the whistles may be used to help individual dolphins pick out others that tend to team up with humans. In effect, they could be labeling themselves as belonging to a specific social group.
[H/T: New Scientist]