DOLPHIN CULTURE
Dolphin Feeding Cultures in Shark Bay
In 1982 an elderly gentleman approached Richard and Rachel, describing a dolphin with a ‘funny growth on it’s nose’ that was found easily if you ‘drive 7 minutes straight north’. On one those two days offshore they did, but saw nothing and with limited time on a borrowed boat, they didn’t linger. Two years later, on a grant from The National Geographic Society, Rachel returned to that area and saw the dolphin with the growth! It looked like the dolphin had a large tumor, and while Rachel was busy feeling sorry for the dolphin, it surfaced without the ‘tumor’. The tumor was, in fact, a marine sponge, and so began the second major line of dolphin discovery in Shark Bay, culture!
Sponges are filter feeding animals that grow on the sea-bottom like a plant. The sponges the dolphins use are cone-shaped and fit nicely on the dolphin’s closed snout like a glove, held on by water pressure. And like a glove, the sponge may protect the dolphin’s snout while it is poking along an abrasive bottom for fish living there. By examining biopsy plugs, we discovered that spongers have a different diet than non-sponging dolphins feeding in the same area; thus the tool gives the dolphins access to different prey. Sponging is a remarkable example of tool use in an animal without hands!
This dolphin’s snout is completely enveloped by a cone-shaped marine sponge it wears for protection while poking around the bottom for prey.
‘Sponging’ is more common in females but is also found in some males whose mothers were spongers. Young dolphins learn sponging from their mothers and is thus an example of a dolphin foraging culture or tradition (some researchers refer to a single socially learned behavior as a tradition and the sum of such behaviors as culture).
Sponges were not the only objects we saw dolphins mucking about with. Occasionally we saw a dolphin surface with a large shell. What was that about? A photograph of a shelling dolphin solved the mystery, the dolphins were shaking a large fish out of the shell! Unlike sponging, which dolphins learn from their mothers (vertical social learning), shelling is learned from peers and is thus an example of ‘horizontal’ cultural transmission. A major focus of our project will be to find out how extensive horizontal cultural transmission is in the Shark Bay dolphins.
A dolphin shaking a fish out of a large shell. Can you see the fish’s tail?
Near the top of Peron Peninsula a handful of dolphins regularly engage in spectacular hydroplaning and beach themselves in pursuit of prey.
Simon Allen took this amazing photograph of a ‘beaching’ dolphin at the top of Peron Peninsula.
In the 1990s, east of Monkey Mia, we saw whale spouts in the distance, only to arrive in the area and find we were with dolphins in only 1.5 meters of water foraging over seagrass beds. Then a dolphin lifted its flukes high out of the water before driving them down forcefully, producing a 3-4 meter high ‘whale spout’ and a ‘kerplunk’ sound that we suspect startles hiding fish into revealing their location to the dolphin. Kerplunking is very common over the seagrass beds east of Monkey Mia but uncommon or absent elsewhere.
A Kerplunking dolphin makes a ‘straining’ sound as she drives her flukes into the water. The kerplunk sound my startle hiding fish into giving away their location.