One of the world’s smallest marine mammals, sea otters are the ocean’s teddy bears and crucial to the existence of marine ecosystems. Celebrate Sea Otter Awareness Week (The last week of September) by learning more about these adorable animals!
River otters reside in coastal waters that are around 50 to 75 feet deep and usually remain within a kilometer from shore. These animals are typically found in places that are protected from harsh weather, such as rocky coastlines, kelp forests and barrier reefs.
Although not considered to be social animals since they hunt, groom, and defend themselves, sea otters often come together in groups called rafts. Rafts of sea otters are either all male or all female and are often made up of 10 to 100 individuals, with the male rafts typically being larger. However, the largest raft ever recorded contained over 2,000 sea otters.
With numbers once ranging from 150,000 to 300,000 individuals, sea otters were a common sight in areas such as the Pacific coast. However, during the years 1741 to 1911, they were frequently trapped for their fur. This tragic plight reduced the sea otter’s population down to as little as 1,000 to 2,000 individuals. Later, in 1938, it was thought that the sea otter was extinct when a raft of 32 sea otters was spotted off the coast of Big Sur California. Over time, conservation efforts have increased the sea otter population to 100,000.
A member of the family Mustelidae along with weasels, minks, and the other 12 remaining otter species, sea otters are quite different in several ways. Unlike all other mustelids, sea otters do not live in burrows or dens, lack a functioning anal scent gland, and can live solely at sea. Because sea otters are so different, in 1982, scientists thought that the sea otter was more closely related to the earless seal than Mustelids.
Sea otters have adapted to their environment extremely well, and although they can walk on the land, these animals are capable of living their entire lives in the water. They can close their ears and nostrils to keep water out during dives, and their feet are flattened and fully webbed, with the fifth toe being the longest. This foot structure makes swimming easier, but at the same time, it makes walking more difficult. Sea otters swim by moving the back end of their body up and down, reaching speeds of up to 5.6mph.
When on the water’s surface, sea otters float along on their backs, moving around by swaying their tails from side to side. On a hot day, they stay cool when resting by keeping their hind legs underwater. On a cold day, however, they stay warm by pressing their legs onto their torso.
The only marine mammal without blubber, sea otters stay warm because of their thick fur; the densest of all animal, with over one million hairs per square inch in areas. Their short underfur is kept dry due to a layer of long, waterproof “guard hairs”. A sea otter’s fur does not shed in a specific season, instead, it sheds gradually year-round. Of course, for their fur to protect them, a sea otter’s coat must be kept clean at all times. Luckily, a sea otter’s loose skin and flexible bone structure allows them to groom every inch of their body.
To be able to float with ease, sea otters are very buoyant animals. This is due to the air in their fur and their large lungs. Sea otters blow air into their fur to keep themselves afloat, and a pup’s coat is so full of air, they cannot sink nor dive. Sea otters also have a lung capacity 2.5 times greater than that of similar sized land mammals.
Sea otters typically mate in autumn, so from Spring to Autumn, male sea otters guard their territory by patrolling its boundaries, keeping other males out; nevertheless, actual fighting rarely occurs. Males without territory often travel amongst female, looking for a mate. The female sea otters are free to move through male territory as they please, where they outnumber the males 5 to 1. Like the North American river otter, sea otters are aggressive when it comes to mating, with the male biting the face of the female to keep her in place, resulting in injury or even death.
Since a sea otter’s gestation period ranges from 4 months to a year, pups are constantly being born. A mother sea otter has 1 pup at a time which she’ll nurse for 3 to 6 months. At birth, sea otter pups weigh around 3 to 5 pounds.
With full grown males measuring about 4 to 5 feet in length and weighing 49 to 99 pounds, and females being smaller, sea otters are the largest mustelid. Nevertheless, they are also the world’s smallest marine mammal.
These animals have a high metabolism and an extremely effective digestive system, with food passing through in as little as 3 hours. For these reasons, a sea otter must eat 25 to 38% of their body weight daily. Sea otters are not picky eaters, consuming over 100 species of prey: mostly marine benthic invertebrates such as urchins, clams, and mussels. Contrary to public opinion, sea otters rarely eat starfish, and the kelp that they eat seems to go through undigested. Sea otters also have large kidneys, which allows them to drink salt water, unlike most marine mammals.
Sea otters are diurnal animals that spend 9 to 12 hours of their day foraging for food on the ocean floor. They usually start an hour before dawn, stopping to nap at about midday. Later in the afternoon, they start foraging one again before stopping at dusk. At about midnight, a sea otter may forage once again, but this is most common in mothers. When a mother sea otter goes to look for food, she wraps her young in kelp to keep them from drifting away. A mother sea otter may also leave her kit in a pen formed by rocks while she forages.
While searching for food, sea otters dive to depths of 50 feet with dives lasting for 5 minutes and use their whiskers to sense for movement in the water. Then they use their specialized paws and retractable claws to catch their prey before taking it up to the surface to eat. Sea otters use stones and have even been spotted using glass bottles and cement blocks, to break the hard shells of their prey. They keep these tools, as well as some food, stored in a pocket of skin, located under their front legs.
Along with seals, sea otters are the only carnivore to have 2 pairs of lower incisors instead of 3. Their teeth are also flattened and rounded to crush their food instead of tear it.
Sea otters aren’t just cute faces; their presence in the wild is vital to our ecosystem since they help to keep the sea urchin population in check. Sea urchins devour the stems of kelp, which causes the kelp to drift away and die, resulting in the destruction of kelp forests. Areas without sea otters are often full of sea urchins and lack kelp forests. Sea otters also remove mussels from rocks, clearing space for other species, thus increasing biodiversity.
With a lifespan of 10 to 15 years for males and 15 to 20 years for females, sea otters are preyed upon by orcas and sea lions, bald eagles are also a threat to young pups. Other than predators, another threat faced by sea otters are disease and parasites, such as Toxoplasma gondii, a parasite found in cat droppings which enter the ocean when cat litter is flushed.
Sea otters are one of the many wonders of the sea, being both adorable animals and crucial to the survival of kelp forests!
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