Which marine mammal uses rocks to open shellfish?
Quick answer
The sea otter is the marine mammal famous for using rocks as tools. Floating on its back, it places a stone on its chest and bangs clams, mussels and snails against it, or hammers shells with the rock, until they crack. It even stores a favorite rock in a pouch of loose skin under its forearm.
Key facts
- Scientific name
- Enhydra lutris
- Range
- North Pacific coasts, from Japan and Russia to Alaska and California
- Weight
- About 14–45 kg; males are larger
- Status
- Endangered (IUCN)
Tool use in the wild
Sea otters are one of the few non-primate mammals known to use tools regularly. Young otters learn the technique by watching their mothers. Researchers have found that individual otters develop personal preferences, and in some areas, worn spots on coastal rocks show where otters have smashed shells for centuries.
The thickest fur of any animal
Unlike whales and seals, sea otters have no blubber. They keep warm with the densest fur of any animal, up to about 150,000 hairs per square centimeter (about a million per square inch). They spend hours grooming to trap a layer of insulating air in it.
To fuel their bodies in cold water, they eat about 25% of their body weight every day.
Holding hands
Sea otters often rest in groups called rafts. While sleeping, they may hold paws or wrap themselves in kelp so they don’t drift apart or out to sea.
Guardians of the kelp forest
Sea otters are a keystone species:
- Otters eat sea urchins.
- Without otters, urchins multiply and chew through kelp.
- Kelp forests disappear, leaving “urchin barrens.”
- Where otters return, kelp regrows, sheltering fish and storing carbon.
Back from near extinction
Hunted for their fur, sea otters fell to perhaps 1,000–2,000 animals by the early 1900s. An international treaty protected them in 1911, and numbers have since recovered to over 100,000, though some populations are still at risk.
Other tool-using animals
- Chimpanzees use sticks to fish for termites.
- Bottlenose dolphins in Australia carry sponges to protect their snouts.
- New Caledonian crows shape twigs into hooks.
- Octopuses carry coconut shells as shelters; see which sea animal can change color.
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