The sea otter is the smallest of all known marine mammals. Comprising of three subspecies, the otter is dispersed along most shorelines of the Northern Pacific Ocean: The Asian sea otter for the Kuril Islands (just north of Japan) to the Commander Islands of Russia, the Northern sea otter from the Aleutian Island of Alaska to Oregon, and the Southern sea otter (the smallest of the three) found in central and southern California. Sea otters are generally not found beyond 2/3 of a mile off shore and in water no deeper than 75 feet. Though primarily found along the coast, we actually have a few individual sea otters here in the San Juan Islands, with Ollie the sea otter a known resident near Victoria BC and the most recent sighting of an otter in the San Juans off the west side of San Juan Island!
Sea otters are generally 50-90lbs and can grow to just under 5 feet long, with largest recorded otter coming in at 119lbs. Males tend to be larger than females as well, with the Asian subspecies being the largest on average. Sea otters are generally brown with lighter colors around the chest and head area, though some individuals could be more yellow or darker black in hue. They get these colors from their fur – the densest fur in the animal kingdom at almost 1 million hairs per square inch. Their dense fur, comprising of a thick undercoat and guard hairs to prevent water from actually touching their body, suffices in the absence of blubber for the cold-water environments in which they live. With long whiskers and webbed hind feet, their weasel shaped bodies are ideal for hunting in coastal environments. Sea otters are commonly seen floating on their back, a behavior indicative of a sea otter instead of a river otter in the same geographical range. Though they have a tail, it is very short and almost unnoticeable – unlike a river otter’s long, thin tail.
Sea otters need to eat. A LOT. These cute, furry, mammals live in cold waters, have a very high metabolism and keep their bodies at 100 degrees Fahrenheit – that takes a lot of energy to maintain. They need to eat ¼ of their body weight A DAY to survive. If this was a 150lb person, they would need to eat 35-40lbs of food a day! So what do they eat? Lots and lots of invertebrates: crabs, snails, urchins, clams, abalone, and mussels. The northern subspecies (found in Oregon, Washington, Canada and Alaska) also eats fish. What is interesting is that species wide they eat at least 33 different prey species, but each individual has a preference for 2-3 items and mainly it that for their entire lives. Mothers pass this on to their pups, so prey preferences can follow family lines!
To catch their prey, they dive (up to 250ft, and as long as 5 minutes) closing their ears and nostrils and using their sensitive whiskers to sense prey in murky waters and strong forepaws to dig in the sea floor for their invertebrate prey. They can get more than one prey item at a time because they have pockets! That’s right, in their forearms they have loose skin where they can stash things – like rocks and food items. Their fur is fashionable and functional! Now, why would I say they stash rocks away? Well, when they come to the surface they need to break open those hard shells of things like clams, mussels and crabs, so they will use rocks to smash the prey against to break them open. This is a great example of tool use! They will also use their environment, hiding extra prey by folding it in kelp fronds so it won’t sink or float away and they can have a snack for later. To eat their prey, they have blunt teeth for crushing, rather than sharp teeth like most other mammal predators.
So foraging takes up a lot of time (and they don’t swim fast, only 3-5mph), but the other part of their day is spent grooming – this is of high importance as without it, they would freeze in their cold water home. Since they don’t have blubber, their hair is what keeps them warm. During grooming the oils from their skin get into the hair and then they fluff it trapping air bubbles, both of these help insulate them against the cold. They are often active at the surface, doing somersaults and diving at the surface – that isn’t just for fun, it helps distribute the air bubbles in their fur creating the best insulation – fun and functional! They can spend up to 8 hours a day grooming, they aren’t vain – it is necessary for their survival!
The typical sea otter day is made up of forage, groom, rest, and repeat (probably a few times)! They spend most of their life at sea, rarely on land (and they are very awkward on land). They will eat, sleep, mate, and give birth in the water. They also like the hang out together – sometimes up to 1,000 individuals in what are called rafts. Safety in numbers, they rest and thermoregulate (maintain their body temperature). Sometimes you will see their front and hind feet up in the air to help conserve heat. They will wrap themselves in kelp so they don’t float away, and perhaps even more adorable is the fact that they will hold hands to help stay together!
Sea otters can live 15-20 years and females usually start giving birth between 2-5 years of age. They put year-round, except in Alaska where it is usually springtime. Gestation time is somewhat variable, with estimates between 6-9 months. This variability is at least partially due to their delayed implantation (like in seals and sea lions) where the fertilized egg does not implant right away. It is stored and will implant a few months later when the timing is right. Pups are born with such dense fur that they cannot dive until they get adult hair. This is helpful for a hungry mom that needs to dive often for food, baby will be happily floating at the surface when she gets back. Sea otters have some pretty nifty tricks up their (pocketed) sleeves!
Sea otters are listed as “endangered” under the IUCN Red List, “threatened” under the Endangered Species Act, and “depleted” under the Marine Mammal Protection Act (MMPA).
Historically their numbers were between 150,000-300,000 animals throughout the Pacific rim. But now, their numbers are drastically depleted: Southern sea otter populations, which were once around 16,000, now hover around 3,000 individuals.
- Fur Trade & Hunting: Sea otters were hunted almost to extinction for their thick pelts from 1741-1911. The craze around sea otter pelts resembled the gold rush, with hunters going to extremes to capture and sell these luxurious pelts to the highest bidder. By 1914 in California, there were an estimated 50 animals left (out of what was believed to be a population that once numbered 16-10,000 animals).
- Direct Human Conflict: Although they are no longer hunted for fur, sadly sea otters still have direct conflicts with humans including shootings, oil spills, and exposure to pollution. Their proximity to coastal waters makes them more susceptible to runoff and pollutants from land as well as those at sea.
- Predation: Killer whales (orcas) are the primary predator of sea otters, and researchers are beginning to suspect that predation from orcas in Alaska may be driving a decline in sea otter numbers.
- Infection & Male Aggression: Female sea otters are at higher risks of infection after giving birth, and can also be subject to aggression from males during this period.
- Biotoxins: Biotoxins produced during algal blooms can be particularly harmful for this species since they spend the majority of their lives in the water.
- Pathogens: Toxoplasmosis (spread through cat litter) and Sarcocystis neurona are two especially detrimental pathogens that can infect and potentially kill sea otters.
- Entanglement: Sea otters will occasionally become trapped or entangled in fishing gear, especially line-based fishing methods.
- Their Latin name, Enhydra lutris, means “in water otter”. Who knew there was a word specifically for otter in Latin?!
- Sea otters are the largest member of the weasel family and the smallest marine mammal.
- They have webbed feet to aid them when swimming.
- Their lung capacity is 2.5 times greater than a similarly-sized land mammal!