Somewhere in the deep channels of Shark Bay, a dolphin is cruising along the seabed with a sponge jammed over her nose like a novelty clown accessory. She is working. She learned the job from her mother, and if she has a daughter, that daughter will almost certainly learn it too.

Sponging, as the researchers call it, is the best documented case of tool use in any wild whale or dolphin. It is also one of the very few animal traditions anywhere that travels almost entirely down the female line.

What the sponge is actually for

A sponger breaks a conical basket sponge off the seafloor and wears it cupped over her rostrum, the long beak. In a 2008 paper in PLOS ONE, Janet Mann of Georgetown University and her co-authors timed the dives of ten sponging females closely enough to show they surfaced with the sponge still on after roughly 77 per cent of dives, then dropped it once a chase began. Since the sponge caps the jaw, it has to come off before anything gets swallowed.

Down there is a rough neighbourhood for a soft nose: broken rubble, spines, stingrays.

Prey explains the rest of it. Eric Patterson and Mann went sponge foraging themselves for a 2011 study, also in PLOS ONE, dragging sponges through the same seabed to see what turned up. The fish being flushed out, mostly barred sandperch, burrow in littered substrate and have no swim bladder, which is the gas-filled sac that bounces back a bright, clean echo. Fish without one barely register on sonar, so a dolphin’s sharpest sense goes soft and rummaging by beak becomes the smarter play.

A skill that stays in the family

Genetics settled the question of how sponging spreads. Michael Krützen and colleagues, writing in PNAS in 2005, used mitochondrial DNA, which an animal inherits only from its mother, to trace nearly every known sponger in the eastern gulf back to a single matriline. That result made sponging the first solid case of material culture in a marine mammal, meaning a behaviour that spreads by social learning.

Numbers have piled up since. By the time Mann’s team published a social network analysis in Nature Communications in 2012, 55 dolphins in the eastern gulf had been logged as habitual spongers, and the authors noted that only the calves of spongers ever become spongers. Even then, not all of them take it up. Eight offspring of sponging mothers never bothered, a useful reminder that this is a tradition rather than a reflex.

Why the sons swim away from it

Male calves watch the whole performance for years and then mostly want nothing to do with it.

That same 2008 study found that sons are exposed to sponging just as often as daughters, yet only 25 per cent of the sons who survived to weaning ever picked up a sponge, against 91 per cent of the daughters.

The favoured explanation is scheduling. Sponging is solitary, slow and hungry for hours, and male Shark Bay dolphins spend their adult lives in alliances, chasing females and holding partnerships together. Male calves are also weaned earlier than their sisters, which shortens the apprenticeship. A dolphin cannot spend the day alone in a deep channel with a sponge on his face and also keep up with the lads.

Manuela Bizzozzero and colleagues, in a 2019 Proceedings of the Royal Society B paper, turned up something neater still: the few males who do sponge tend to associate with other male spongers, whether or not they are related, which suggests the tool itself may be drawing them together.

The tool comes with a bill

Sponging is “cognitively demanding and difficult to master”, in the words of Ellen Jacobs of Aarhus University, who led work published in Royal Society Open Science in 2025. Her team ran computer models of sound moving through real sponge tissue and found that wearing one distorts the clicks a dolphin sends out and the echoes it gets back. Every hunt with a sponge means working around a sabotaged sense.

One detail from that modelling is quietly lovely. As reported by Georgetown University, the sponge species the dolphins reach for most often, Echinodictyum mesenterinum, interferes with echolocation less than the alternatives, which hints that the animals are not grabbing whatever is nearest.

That difficulty may be the whole reason the tradition stays sealed inside a handful of families. Spongers mix with non-spongers constantly, and no dolphin outside those matrilines has ever taken the habit up. Outsiders occasionally try it once and never come back to it, while a calf raised by a sponger logs thousands of hours watching the technique before attempting it.

Not every dolphin tradition works this way

Shark Bay has a second tool trick called shelling, in which a dolphin chases a fish into the empty shell of a giant sea snail, lifts the shell clear of the water and tips the contents into its mouth. Sonja Wild and colleagues tracked it across eleven years of boat surveys for a 2020 paper in Current Biology, logging 42 shelling events by 19 individuals, and concluded it spreads sideways between associates, moving through friendships more than family lines.

Still, that is a single analysis of a behaviour observed only a few dozen times.

Mann told Science News at the time that the researchers may have been quick to rule out environmental and maternal factors, since where shells sit on the seabed shapes who can use them at all.

Sponging sits on much firmer ground, and what it documents is closer to an inherited career than a clever party trick. Years of practice, a specialised stretch of seabed, a diet no other dolphin in the bay can reach, and a social life bent around the hours the work demands, all of it handed to a daughter who was there for every stage of the training.