Sea Otter
SEA OTTER (Enhydra lutris)
The sea otter is one the smallest marine mammals and is the heaviest member of the weasel family. These adorable animals live along the coasts of North America and eastern Asia, where they forage for invertebrates, sometimes utilizing rocks to open mollusk shells. Unlike other marine mammals, they do not have a blubber layer, instead insulating themselves with the thickest fur in the animal kingdom. Sea otters are still classified as endangered, and represent a critical keystone species in the ecosystems they inhabit.
Difficulty: Easy
Sea Otter Description
Sea otters are one of the smallest marine mammals, and are the largest member of the mustelid, or weasel family. Male sea otters can weigh over a hundred pounds, with females reaching weights of around seventy-five pounds. They are unique among marine mammals in utilizing thick fur, rather than blubber to keep themselves warm. In fact, they have the thickest fur of any animal with close to a million hairs per square inch. These hairs, a combination of a short underlayer, covered with guard hairs traps air inside, keeping water from ever reaching the animal's body. Sea otters keep their feet held up out of the water to stay warm, or will lower them into the water on hot days. Like other weasels, sea otters have a highly flexible spine, which they use readily to dive and forage for food. Their whiskers, front paws and eyes are utilized when searching for prey. Female otters can often be identified by their wounded noses, which is caused from males biting them during mating. As sea otters mature, their faces turn white in color.
A southern sea otter is wrapped in seaweed to keep from floating away. Sea otter faces turn white as the animal ages. You can see this individual groom its thick fur, making sure it keeps its insulating properties as the animal has no blubber.
Sea Otter Distribution and Habitat
Sea otters are found in the northern Pacific Ocean, along North America, Russia, and Japan. They are a coastal species, generally being found within a mile of the shoreline. Sea otters utilize coastal ocean 15 to 23 meters (49 to 75 ft) deep, where they forage for their food. They are classified as three different subspecies, found in nine distinct and seperate populations. During our sea otters and whales of Monterey Bay photo tour, we encounter southern sea otters, which are found along the central and southern coasts of California, and are the smallest subspecies of sea otter. Sea otters do not migrate, and are found year around in Monterey Bay, where we hold our tour. This area has been a stronghold for the southern sea otter population which is numbered around 3,000 individuals. Sea otters are somewhat adaptable to human change, and can be found resting in harbors.
A male Sea Otter rests along the cost of Monterey Bay, California, where we hold our tour. Sea Otters are almost always found within one mile of the coast.
Sea Otter Feeding Biology
Sea otters feed on a variety of prey, mostly invertebrates and some species of fish. Their invertebrate diet includes urchins, clams, mussels, crabs, and worms, amongst others. In the area we photograph the otters, they are often feeding on Fat Inkeeper Worms, which we have observed feeding over and over again. To catch their prey, they dive down to the ocean bottom, holding their breath for up to five minutes, but generally come up after around one minute. Sea otters are one of the few mammals that use tools, using rocks to dislodge prey and to open shells. Some sea otters have favorite cracking rocks, storing it in a pouch of loose skin behind its foreleg. They may even store prey in this pouch before bringing it to the surface. Upon arriving back to the surface with their prey, they flip onto their back, to either crack open the mollusk shell with a rock, or start tearing apart their prey using their front feet and mouth. Sea otters mostly feed at dawn and dusk. Depending on the density of otters, they may spend up to 60% of their daily activities foraging. They require up to 7,500 calories a day, which is equal to eating about 25% of their own body weight in food each day.
Sea otters are known as a keystone species as they have a significant impact on the ecosystem they live in. Without their presence, sea urchins take over, grazing down and eliminating kelp forests from the area. Since sea otters feed on urchins, they keep their numbers in check allowing kelp forests to flourish.
Sea Otter (Enhydra lutris) mother giving pup Fat Inkeeper Worm (Urechis unicinctus) prey to feed on, Monterey Bay, California
Sea Otter Social Organization
Sea otters are solitary when feeding, unless it is mothers and their pups. When resting sea otters however tend to gather in same sex rafts. These rafts can number up to a hundred animals, but generally are around ten animals. In the Monterey Bay, where we photograph sea otters, rafts are generally no more than five or six animals. To keep themselves from floating away, sea otters will wrap themselves in kelp, or seaweed, or may even hold hands amongst individuals. When there is no human disturbance, sea otters may even rest on shore. Females do not hold territories though often utilize the same area over and over. This is in contrast to male sea otters, which do hold territories they defend, though generally only during the mating season. Males will fight to defend this territory, as it provides access to females, which generally outnumber the males five to one.
Sea otters utilize a few different vocalizations to communicate with pups calling their mothers being the most commonly heard sound during our tour. When mothers leave their very young pups at the surface, they will often call with a high-pitched scream like sound repeatedly, until their mother places them back on her belly. When pups are older, and foraging with their mother, they will utilize the same scream to find their mom if they become separated. The mother's call to her pup is similar, though lower in pitch. Distressed otters may whistle or hiss.
Sea Otter (Enhydra lutris) males in raft, Monterey Bay, California. These rafts can have up to a hundred sea otters, though generally are around six to ten animals.
Sea Otter Reproduction
Sea otters are polygamous, with males having multiple female partners. The females a male will mate with is generally determined by his territory. Some sea otter males however swim into female rafts and check for individuals that are in estrus. During her three day cycle, the male and female will engage in playful, but also sometimes aggressive courting behavior. While mating the male will bite the females nose to hold on, often leaving visible wounds on her nose.
Gestation lasts from four to twelve months and delayed implementation is possible for the species. Births occur all year long, with peak seasons in the Monterey Bay occurring January through March. Generally, just one sea otter pup is born, weighing around four pounds. Until about thirteen weeks, the pup's fur is light brown, and is so thick that the pup is incapable of diving. This helps the pup stay warm, and buoyant, especially when the female is on foraging dives. During these first three months of life, sea otter moms mostly carry their young on their belly as they rest as swim along the surface.
Sea otter pups will nurse for their first six to eight months, with mom offering food at around one to two months. Juveniles are typically independent after weaning, being able to forage on their own, though may link up with their mother to forage and feed together. During our tour, we often observe older sea otter pups as they beg for food from their mother, who most of the time are more than willing to share.
Female sea otters become sexually mature at around three to four years of age and males at around five years of age. They can live up to twenty three years in the wild, though most lifespans are shorter.
Sea Otter (Enhydra lutris) mother carrying young pup on belly, Monterey Bay, California.