Why Do Sea Otters Carry Rocks? Meet the Ocean's Toolmaker
Why do sea otters carry rocks? Because they use them as tools. A sea otter dives for a clam or a snail, floats on its back, sets a stone on its chest and smashes the shell open. And between dives, it often keeps that rock tucked in a pocket under its arm.
Quick Facts
- Species: Sea otter (Enhydra lutris)
- Pockets: A fold of loose skin under each forearm
- Fur: More than a million hairs per square inch
- Appetite: About 25% of body weight a day
- Known for: Tool use and holding paws while resting
The Pocket Under Each Arm
NOAA describes baggy pockets of loose skin under each forearm. Sea otters use them to store food they've gathered on a dive, and to keep favorite rocks for cracking open shellfish. That leaves their paws free to keep hunting.
No Blubber, So They Eat a Lot
The sea otter is the only marine mammal without blubber, according to NOAA. Staying warm in cold water burns a lot of energy, so the National Park Service says adults can eat 25 to 30 percent of their body weight in a single day.
The Densest Fur of Any Mammal
Instead of fat, sea otters rely on fur. The Monterey Bay Aquarium says their coat has more than a million hairs per square inch, and the National Park Service calls it the thickest fur of any mammal. Otters groom constantly to keep air trapped in it, because matted fur stops insulating.
Accidental Forest Rangers
Sea otters eat sea urchins, and urchins eat kelp. Where otters disappear, urchins can strip kelp forests bare, leaving what scientists call urchin barrens. Where otters are healthy, the Monterey Bay Aquarium explains, they keep urchins in check and the kelp forest can thrive. That makes them a keystone species.
Do Sea Otters Really Hold Hands?
Sometimes. Sea otters rest in groups called rafts, and some wrap themselves in kelp so they don't drift while they sleep. Resting otters have been seen holding paws, which may help keep them together.
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Frequently Asked Questions
Why do sea otters carry rocks?
They use rocks as tools to crack open clams and other shellfish, and they can stash a favorite rock in a skin pocket under their arm.
Do sea otters have pockets?
Yes. A fold of loose skin under each forearm works like a pocket for food and rocks.
Why do sea otters hold hands?
Resting otters sometimes hold paws, and some wrap up in kelp, which helps them avoid drifting apart while they sleep.
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- Loggerhead Sea Turtle Hatchlings
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For Otter Fans
Gift idea
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Sources
- NOAA Ocean Today: Sea Otter Anatomy: forearm pockets, no blubber, dense fur
- National Park Service: Sea Otter: fur density, daily food intake, tool use
- Monterey Bay Aquarium: Sea Otter: fur, urchins and kelp forests
- NOAA Ocean Today: Sea Otters 101: sea otter basics
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