Australasian Science: Australia's authority on science since 1938

Dolphins Go Fishing with Conch Shells

By Stephen Luntz

One of the remarkable behaviours of the bottlenose dolphins of Shark Bay in Western Australia appears to be becoming more common, opening up exciting questions about these intelligent animals.

Shark Bay dolphins are known for sponging, where females of certain lines carry marine sponges on their noses while searching for bottom-dwelling fish (AS, October 2009, pp.20–22). Other dolphins in the area have also been seen half-stranding themselves to catch fish near the beach and “conching”. This involves picking up a conch shell containing a fish, bringing it to the surface and shaking the water out, bringing the fish with it. The dolphin then eats the displaced fish.

“Obviously the shaking about of the shell and the manipulation of the object implies some degree of problem-solving,” says Murdoch University PhD student Simon Allen. “The dolphin has worked out it has to lift the shell up and shake it about so the water comes out and the fish falls into its mouth.”

Conching has not been observed often, but half the observations happened this year, raising the intriguing possibility it is becoming more common. Most dolphins that have been seen conching are from the western gulf and spend a lot of time together.

Allen stresses it is speculation that the behaviour is spreading horizontally among the dolphins rather than vertically from mother to daughter, as sponging does. If this is the case he thinks it may be because “conching is easier to pick up, if you’ll pardon the pun,” requiring less learning.

Another exciting possibility has the dolphins using the conch shells as traps, turning over abandoned shells so that fish will swim into the apparently safe haven. Allen is keen to check this with underwater photography, and also to set shells in particular locations and see whether the dolphins disturb them to see if there are fish inside.

Dolphins may also witness fish they are chasing hide in shells. Allen doubts that even the dolphin’s remarkable echo­location would allow them to detect fish inside shells.

Bottlenose dolphins are particularly adaptable, surviving in areas where industrialisation has wiped out other cetacean species. Allen attributes the particular flexibility of the Shark Bay population to the productivity and diversity of the environment in which they live.