Do dolphins use tools to feed?

Tool use was long regarded as a distinctive mark of human intelligence. Then it was found in the great apes. Then in corvids. Then in sea otters. And then, in one of the most fascinating findings of marine ethology, in several populations of dolphins. The best known technique, called sponging (“sponge fishing”), is a window onto the cognitive and cultural capacities of cetaceans.

Sponging in Shark Bay

It begins in Western Australia, in Shark Bay. Since the mid-1980s, a team of biologists, in particular Janet Mann and Rachel Smolker, has been studying a population of common bottlenose dolphins that shows a unique behaviour: some individuals detach conical marine sponges (of the genus Echinodictyum) from the seabed and slip them over their rostrum, like a glove or a thimble.

The purpose of the technique is to probe sandy and rocky bottoms in search of hidden prey. The sponge protects the dolphin’s delicate rostrum from stings, sharp corals, spines and shells. Without that protection the animal would probably give up this bottom-foraging strategy.

An exclusive ecological niche

What makes sponging particularly interesting is not only the use of a tool, but the fact that it opens an ecological niche that other dolphins cannot reach. The prey sought are in particular sandperches (Parapercis nebulosa), small fish that bury themselves in the sediment.

A crucial point: these fish have no swim bladder, the gas-filled organ that makes most fish easy to detect by echolocation. “Ordinary” dolphins therefore do not pick them up. The “sponging” dolphins flush them out of the sand by probing directly. This feeding niche is accessible only to those that master the sponge technique.

A strictly matrilineal transmission

Genetic studies have revealed something more remarkable still: sponging is passed on almost exclusively from mother to daughter. Young females learn by accompanying their mother for years, watching her movements and trying the sponges themselves. This vertical transmission between females forms a genuine matrilineal line of specialists.

Young males, for their part, rarely learn the technique. This sex asymmetry remains unexplained, perhaps linked to the dispersal of males at maturity, which interrupts transmission, or to social dynamics specific to males, who favour other forms of cooperation (the well known “male alliances” of Shark Bay).

Beyond sponging

Sponging is not the only documented example of tool use in dolphins. Also in Shark Bay, shelling has been observed: some dolphins chase fish into large empty gastropod shells (conches in particular), then bring the shell to the surface to let the trapped fish slide straight into their mouth. This technique, more recent still, also appears to be spreading culturally.

In other parts of the world, dolphins have been observed using fragments of coral, pieces of seaweed, even floating scraps of plastic, in play or exploratory behaviour. The inventiveness of dolphins faced with objects in their environment appears to be one of the main sources of behavioural innovation in cetaceans.

Animal culture: fundamental implications

Shark Bay sponging is now regarded as one of the best documented examples of animal culture. It meets every criterion: it is a learned behaviour (not innate), it varies between populations (not all common bottlenose dolphin populations practise it), it is passed on by social learning, and it is stable over several generations.

The finding has major philosophical and biological implications. It confirms that the idea of culture as exclusively human is obsolete. Several non-human species, chimpanzees, dolphins, sperm whales, humpback whales, have cultures in their own right, with their traditions, their innovations, their transmission across generations. Conserving these species means conserving not only their DNA but also their cultural heritage, a heritage of which every population that disappears takes unique techniques with it, lost for ever.

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