The sea otter (Enhydra lutris) is a marine mammal known for spending nearly its entire life in the ocean. Unlike seals or sea lions, otters rarely haul out onto land, meaning they must manage all life functions, including sleep, while floating on the water’s surface. Their survival depends on specialized behaviors that counteract the ocean’s strong forces and potential dangers while they are asleep.
Where and How Sea Otters Rest
Sea otters sleep almost exclusively on the surface of the water, a habit that distinguishes them from many other coastal mammals. The typical resting position involves floating on their backs, a posture that keeps their snout and nostrils clear of the water. This supine float allows them to relax while minimizing energy expenditure in the cold marine environment.
During resting periods, an otter often folds its front paws across its chest or drapes them over its eyes. This keeps the sensitive pads warm and dry above the water line. Otters possess highly dense fur, which relies on a layer of trapped air for insulation. Keeping the paws out of the water also helps minimize heat loss through these poorly insulated extremities.
Before settling down to sleep, an otter meticulously grooms its coat. This action fluffs the fur, replenishing the insulating air layer that protects them from the cold waters. Maintaining the integrity of this air barrier is crucial, as a wet or matted coat can lead to rapid heat loss and hypothermia.
The Social Strategy of Rafting
Sea otters frequently employ a social resting strategy by gathering in large groups known as rafts. These rafts can range in size from a few individuals to aggregations sometimes exceeding one hundred otters. The grouping provides mutual benefit, offering collective security against predators and conserving body heat.
To maintain the cohesion of the raft and prevent members from drifting away in the currents, otters often hold onto one another. This well-known behavior involves linking paws or forelimbs with a neighboring otter on either side. The resulting intertwined chain helps stabilize the entire floating unit against the constant movement of the waves.
The presence of multiple otters increases the likelihood that at least one member remains vigilant, offering shared watchfulness. This collective strategy is particularly beneficial for mothers and pups, as the group provides a buffer against environmental disturbances.
Anchoring to Avoid Drifting
A major threat to a sleeping otter is being carried out to sea by strong tides and currents. Being swept away from established foraging grounds or sheltered coastal areas can be dangerous and inefficient. To counteract this drift, otters utilize the surrounding marine vegetation.
This solution involves using kelp, a large type of brown seaweed, as a natural, biological anchor. The otters seek out dense kelp beds that are firmly rooted to the ocean floor, forming underwater forests. These beds provide a relatively calm environment and a fixed point to which the otter can tether itself while resting.
An otter achieves stability by physically wrapping strands of kelp fronds around its body, creating a temporary leash. They secure themselves by making several turns around their torso, binding themselves to the stationary plant. This action ensures the otter remains within the safety of the kelp forest. Sometimes, an otter secures a single limb or tail to a piece of kelp, which is enough to counteract gentle currents.
Failure to anchor properly can result in the otter being transported many miles from its home range, requiring significant energy expenditure to swim back. Therefore, selecting a suitable kelp bed and using a secure wrapping technique are important survival mechanisms.