Despite being a keystone species in important ecosystems that span the northern and eastern North Pacific Ocean, sea otters have historically had a complex and sometimes troubling relationship with humans.
Sea otters share common ancestry with a family called Mustelidae, a diverse group of organisms that include 12 other otter species and small terrestrial animals such as weasels and badgers. Like other mustelids, sea otters are small animals that have short legs, short round ears, and thick fur. However, unlike their closest relatives, sea otters do not make burrows, often live their entire life on water, and lack anal scent glands. Though it is considered to be one of the smallest marine mammals, it is the heaviest mustelid, weighing between 50 to 100 pounds.
Although sea otters are known for being playful and sociable, they are not true social animals, often spending time alone to hunt, groom, and defend itself against predators and its territory. Still, sea otters do interact with one another in profound ways, often cooperating with one another to survive: they rest together in small groups called rafts, typically containing 10 to 100 animals and even hold paws while sleeping to prevent themselves from drifting apart. Living in a polygynous society, male sea otter have multiple partners and rely on the female to perform all tasks of raising the offspring. Female sea otters are known to provide her offspring with constant motherly affection and support, and because pup mortality is high, experienced mothers have the greatest successes.
Devoid of blubber, sea otters rely on extremely think fur to regulate their body temperature. With the highest density of hair per square inch for any animal, the fur acts as a waterproof guard, ensuring that cold water is kept away from the skin and heat is retained. Despite adaptive value in the natural world, this unique morphological character has historically led to a rapid decline in sea otter populations.
Though evidence indicates that indigenous people have long killed sea otters for fur, wide-spread hunting took place during the 18th and 19th century, ultimately reducing hundreds of thousands to just a few thousand individuals. However, due to the efforts of dedicated environmentalists and policy makers, sea otters rebounded in nearly two-thirds of their historic range.
While the recovery is considered one of the greatest successes in marine conservation, sea otters are classified as endangered, still vulnerable to many anthropogenic threats, including oil spills, poaching, commercial fishing, and climate change.