Chapter 1
Bodies Built for Water
Picture yourself as a river otter in a cold stream. Your long body bends like a ribbon. Webbed feet push the water back, and a thick tail steers. How does every part help you swim?
Paddling and steering
A river otter swims with webbed feet and a muscular tail. Wide webbed paws paddle through rushing water. The thick tail acts like a rudder to steer.
To swim fast, an otter bends its flexible spine up and down in waves. Each wave pushes it forward.
Warmth without blubber
Unlike seals, otters have no blubber to keep them warm. Instead, a sea otter has the thickest fur of any mammal on Earth.
Long guard hairs lock together like a zipper over the soft underfur. Beneath them, tiny air bubbles stay trapped against the skin. This blanket of air keeps cold water off.
Caring for the coat
A sea otter spends three to five hours every day grooming. It rubs its coat with its paws to spread natural oils. Then it blows air deep into its fur.
Dirty, tangled fur lets cold seawater reach the skin. Then the otter loses heat fast. Grooming is not just for looks. It keeps the otter alive.
River otter or sea otter?
North American river otters live in rivers, lakes, ponds, and marshes. Their webbed paws have sharp claws, and their thick tails taper to a point.
Sea otters live almost their whole lives in the ocean near the coast. Their hind feet are wide flippers, and their tails are short and flat.
Chapter 2
Life in the River
Have you ever slid down a snowy hill on your belly? A river otter does too. It tucks its front legs to its sides and zooms down a muddy bank. Splash!
Sliding on mud and snow
River otters slide belly-down along muddy banks, grassy slopes, and snowdrifts. In cold northern winters, they do not hibernate. They run and slide across the frozen ground instead.
Sliding is not just play. A long belly slide saves energy, so it is an easy way to travel.
Safe inside the den
A river otter's den along the bank is called a holt. River otters do not dig dens. They move into old beaver lodges, muskrat burrows, or hollow logs.
The way into a den is usually an underwater tunnel. Land predators cannot easily follow. Inside, a mother otter keeps her pups safe.
Growing up in the family
A mother river otter usually has two or three pups in early spring. The pups are born blind. Their eyes open after about a month.
The mother raises the pups alone, because males do not help. At about two months, she coaxes the pups into the water and teaches them to swim.
Playful learners
River otters are playful. They wrestle, chase each other, and play tag in the water. They also juggle pebbles.
Play is also practice. Wrestling and chasing build strong muscles and quick moves. Those skills help a river otter catch fish, crayfish, and frogs.
Chapter 3
Life in the Kelp
Could you nap on the ocean with no bed or boat? A sea otter can. It floats on its back near the coast, wrapped in kelp so it does not drift away.
Diving for dinner
An otter seals its ears and nostrils shut when it dives. Holding its breath, it hunts underwater for food. A sea otter usually stays down for one to two minutes.
A sea otter's lungs are about two and a half times the size of a similar land mammal's. The extra air helps it float.
Whiskers that feel in the dark
Water under the kelp can be dark. Otters hunt there with stiff whiskers called vibrissae. Many nerves wrap around the base of each whisker.
The whiskers feel tiny ripples made by fish, crabs, and clams. So an otter can find food it cannot see.
Anchored in the kelp
Sea otters wrap kelp around their bodies when they rest. Floating together in groups called rafts, the otters stay anchored against wind and currents.
Giant kelp is rooted to the seafloor and grows up to the surface. It works like an anchor rope. Wrapped in kelp, an otter can sleep safely on its back.
Floating together in rafts
Sea otters often rest together in floating groups called rafts. A raft can hold just two or three otters, or hundreds floating side by side.
Males and females usually rest in separate rafts. Resting otters sometimes hold paws so they do not drift apart.
Chapter 4
Clever Claws and Tools
Can you hear that tapping out on the waves? Clack! Clack! Clack! A sea otter is floating on its back with a flat stone on its chest. Sea otters are among the few mammals that use stone tools.
The chest anvil
Sea otters use flat stones as anvils on their chests to crack hard shells. A sea otter can tuck its stone into a skin pouch under its arm between dives.
The otter sets the stone on its chest. It grips a clam in both front paws and pounds it on the stone until the shell breaks.
Built-in pockets
Under each front leg, a sea otter has loose, stretchy skin. This armpit pouch works like a pocket. The otter uses it to carry food and rocks to the surface.
Some sea otters have a favorite stone. They keep it tucked under an arm from one dive to the next.
Cracking tough shells
Sea otters eat mostly animals without backbones, such as sea urchins, crabs, clams, and snails. Their broad, flat back teeth crush thick shells.
Sea otters are the only carnivores with just four lower front teeth. Other carnivores have six. These four teeth form a scoop that scrapes meat out of shells.
Clever paws
A sea otter's front paws are small and nimble, with tough, sensitive pads.
Sea otters do not swim with their front paws. Their hind flippers do that job. The front paws hold tools, groom fur, and grab food.
Chapter 5
Clean Waters and Recovery
What would an otter in a river near you tell you? River otters need clean water. Out at sea, sea otters help kelp forests grow.
Guardians of clean water
River otters need clean water, so river otters are a sign of a healthy river. Sea otters thrive in protected ocean areas with plenty of food.
In dirty rivers, poisons such as mercury build up in fish and crayfish. When a river otter eats them, the poisons collect in its body.
Saving the kelp forests
Sea otters are a keystone species. Without them, sea urchins multiply and chew through the bases that anchor the kelp. The forest becomes a bare place called an urchin barren.
When sea otters eat urchins, kelp forests stay tall and shelter fish. Growing kelp also takes in carbon dioxide.
Returning to rivers
In the 1900s, pollution and trapping wiped out river otters in 11 states. Starting in 1976, wildlife workers moved more than 4,000 otters to new homes.
They were released in more than 20 states. Today, river otters live again where they had been gone for years.
Saved from extinction
In the 1700s and 1800s, fur traders hunted sea otters across the North Pacific. By 1911, a population of up to 300,000 had fallen to fewer than 2,000.
In 1972, a United States law gave sea otters even more protection. Slowly, the small groups that survived began to grow.
Modern dangers
In 1989, the Exxon Valdez oil spill killed thousands of sea otters in Prince William Sound. Oil ruined the air trapped in their fur, and many froze.
A parasite from cat droppings washes down rivers to the sea. Southern sea otters catch it from shellfish, and it can kill them.
Your next question
Choose a picture. Say what you see. Ask a question it cannot answer. Find a helpful page or explore with a grown-up.
Otter quiz
Do otters have blubber to stay warm?
Show the answer
No. Their fur traps a layer of air.
How do river otters travel fast on snow?
Show the answer
They tuck their front legs and slide on their bellies.
What do sea otters wrap around themselves?
Show the answer
Giant kelp.
Where can a sea otter carry its stone between dives?
Show the answer
In a pouch of loose skin under its arm.
Why are sea otters called a keystone species?
Show the answer
They eat sea urchins, which saves kelp forests.
Can river otter pups swim when born?
Show the answer
No. Their mother helps them learn.
Glossary
- anvil
- A flat stone a sea otter holds on its chest to crack hard shells.
- guard hairs
- Long outer hairs that lock together to keep the underfur dry.
- holt
- A river otter's den along a riverbank or lakeshore.
- keystone species
- An animal that keeps its whole habitat in balance.
- pouch
- A skin pocket under a sea otter's arm for food and stones.
- raft
- A floating group of resting sea otters.
- vibrissae
- Stiff, sensitive whiskers that feel water movements to find food.
How we know
A useful explanation starts with evidence. Ask what was seen, and what still needs a test.