Swimming
Otters are excellent swimmers. They swim with movements of the hind legs and tail. Freshwater otters "dog paddle" with all four feet when swimming slowly or floating. When swimming at a high speed, the entire body, including the tail, undulates up and down and the hind feet steer.
Researchers have observed giant otters swimming at speeds up to 14.4 kph (9 mph).
Sea otters spend a great deal of time floating on their backs at the surface. They move by paddling their hind limbs and sculling with their tails. For rapid swimming and for diving, they swim similarly to other otters, using up-and-down undulations of the body. Sea otters can reach speeds of 1.5 kph (0.9 mph) on the surface and 9 kph (5.6 mph) under water.
Diving
River otters can remain under water for 6 to 8 minutes.
Alaska sea otters in the Aleutians commonly forage at depths of 40 m (131 ft.) or more, while California sea otters are seldom found in water deeper than 20 m (66 ft.). Sea otters usually remain submerged for 52 to 90 seconds; the longest recorded dive was 4 minutes, 25 seconds. Such extended dives are probably a response to danger. The deepest confirmed dive for a sea otter was 97 m (318 ft.).
Locomotion on Land
River otters may travel considerable distances over land between waterways. Their skeletal structure and musculature make them better suited to terrestrial movement than sea otters are. River otters can attain running speeds up to 47 kph (29 mph). They travel over snow and ice using a combination of running and sliding.
Sea otters are quite awkward on land, and spend the majority of their lives in the water.
Thermoregulation
Heat conductivity in water is 27 times faster than in air of the same temperature. Even in temperate water mammals lose body heat rapidly.
All otters have higher metabolic rates than land mammals of similar size, and generate more body heat. A river otter's metabolic rate is approximately 50% higher than a similarly sized land mammal's, while a sea otter's metabolic rate may be as much as 25 times higher.
The higher metabolic rate necessitates a higher caloric intake.
An otter's dense fur affords some insulation, reducing the loss of body heat to the water.
For sea otters, maintaining a constant body temperature is particularly challenging. Alaska otters typically inhabit water that may be as much as 15.5°C (60°F) below their core temperature.
Unlike other marine mammals, sea otters lack an insulating layer of fat. They rely on a higher metabolic rate and air trapped in their dense fur.
The cuticle of each hair is scaly and ratchet-like. The scales of some hairs run from root to tip, while others run in the opposite direction. This arrangement allows hairs to interlock.
Minute spaces between the hairs trap air effectively. Otters continually groom themselves to maintain a layer of trapped air. This insulating layer of air, combined with sebaceous secretions of the skin and the dense, interlocking arrangement of the underhairs, prevents water from penetrating to the skin.
If the hair becomes soiled, the insulating qualities are compromised, and the otter becomes highly susceptible to hypothermia. Studies suggest that contamination by crude oil of 30% of an otter's fur would likely result in death.
Sea otters may have a countercurrent heat exchange system. Arteries and veins in the extremities are very close together. Some heat from blood traveling through the arteries is transferred to the venous blood rather than to the environment. This system may aid otters in conserving body heat.
Sea otters often hold their feet out of the water. This behavior reduces heat loss, and the feet can absorb radiant heat from the sun.
