The sea otter (Enhydra lutris) is a large otter native to the North Pacific, from northern Japan and Kamchatka east across the Aleutian Islands south to California. The heaviest of the otters, sea otters are the only species within the genus Enhydra.
They were hunted extensively for their luxurious fur. Its estimated that a half million to a million otters were killed over time. The population is thought to have been 150,000 to 300,000 historically before the years of the great hunt. Although several subspecies are still endangered, the otters have since been legally protected, and reintroduction efforts have shown positive results in some areas.
Exceptionally thick brown fur insulates the animal and retains air. The sea otters have sebaceous gland secretions of squalene (normally found only in minor concentrations in other mammals). This creates an effective barrier between the water and the skin and acts as a substitute for subcutaneous insulating fat. Underneath each powerful front flipper is a pouch of skin used to temporarily store food collected during extended dives to the bottom. The front flippers also have retractile claws, while the hind flippers are longer, broadly flattened and webbed. The fifth digit on the hind flipper is the longest, unlike that of any other mammal. This makes walking on land difficult. Sea otters have a fairly short, thick, muscular tail. They have no scent glands.
They have specially adapted spinal columns and bone structure to allow great flexibility. Sometimes the bones will be dyed pale violet from eating purple sea urchins. They have 38 chromosomes. Sea otters have large lung capacity 2 to 4 times greater relative to size. Sea otters store 66% of their oxygen in their lungs, so the large lungs are well suited for their brief shallow dives. This also helps with buoyancy.
Sea otters have a highly unique eye development for mammals leading to an accommodation at least 3 times greater than any other mammal. This enables them to see clearly and focus on objects above and below water. Sea otters have compact molars with smooth cusps. They are the only carnivore with no more than four lower incisors. Male sea otters may reach a maximum weight of 100 lb (45 kg) and a length of up to 5 feet (1.5 m). Females are smaller. Males are generally 35% heavier and 8% longer and have heavier heads and necks.
In the wild the sea otters live perhaps 15 to 20 years, and can live longer than 20 years in captivity.
Habitat and diet
Generally sticking to shallow coastal waters of no more than about 181 feet (55 m) in depth, sea otters are found most often in areas with rocky coastline and thick kelp forests. Barrier reefs and intertidal areas are also inhabited. These otters may be considered a keystone species. They control the population of certain invertebrates that would otherwise run amok if unchecked. To eat prey in shells they often use rocks, which sit on their stomach, to break open the shell in order to get the creature inside.
Crabs, mussels, scallops, cephalopods, fish, chitin and snails are also prey to the sea otter. Individuals may show finicky preferences. Despite this, they require 20-25% of their body weight in food each day. They may forage for prey as often as every 5 hours. Their metabolism is high. Also these small mammals can lose heat easily to their aqueous environment as of water’s high thermal conductivity. Sea otters consume more seawater than most any other marine mammal.
Their mothers teach otters feeding practices, and groups of otters often show matrilineal differences in food preferences. Some lineages of otters are noted for their preference for gulls or sand crabs as food sources.
Otters frequently eat while floating on the surface of the water. Otters like to relax and groom themselves this way after a hunt, and also use this method to fill up their fur with warm air bubbles for insulation.
Sea otters may be either solitary or in groups called rafts when resting and cling to kelp so they do not float away while they are taking a nap. Females avoid males outside of breeding periods and the otters segregate into male and female areas.
Diurnal animals, foraging and grooming take up most of a sea otter’s day. Feeding activity peak in the early morning and evening. Dives is fairly short, typically lasting no more than about 90 seconds. The otters wrap themselves in mats of kelp, securing them from the sway of currents while resting and feeding. Floating on their backs, the otters wash and (if necessary) pry open their prey with a favored rock they keep in their pouch. Sea otters present a rare example of mammalian tool use.
Sea otters can be cute and cuddly yet one must remember that they are large carnivorous mustelids with sharp teeth and a high dexterity so approaching or grabbing one can spell trouble.
Breeding & Reproduction
No set-breeding season is observed, but peaks occur from May to June in northern populations and January to March in southern populations. Males reach sexual maturity around 5 to 6 years and have been known to still have offspring at 19.