Tag Archives: Alaskan Sea Otters

What Do Sea Otters Eat?

November 4, 2018Kodiak Wildlife, Sea OtterAlaskan Sea Otters, Do sea otters eat fish, Kodiak Wildlife, Robin Barefield, Sea Mammals of Alaska, sea otter, What Do Sea Otters Eatadmin

As I told you last week, a sea otter burns calories at a rapid rate to help maintain its body temperature in its home in the cold North Pacific. It consumes between 23 and 33 percent of its body weight per day, so a fifty-pound otter eats 11 to 16 lbs. (5 to 7.3 kg) of food every day. Where does a sea otter find this much food, and what do they eat?

Sea otters are known to consume more than 150 different prey species, mostly slow-moving benthic invertebrates such as mollusks, crustaceans, and echinoderms, but if they are hungry enough, they also sometimes eat fish and even seabirds. Sea otters are the only marine animals capable of lifting and turning over rocks in search of prey and the only marine mammal that catches fish with its forepaws rather than with its teeth.

Studies done in southeast Alaska, Prince William Sound, and near Kodiak Island indicate that clams are the primary and preferred prey of sea otters in these regions. Clams constituted anywhere from 34% to 100% of the diet of sea otters near Kodiak. In areas where clams are less plentiful, and in areas where otters have depleted the clam populations, mussels and sea urchins comprise a larger percentage of otters’ diets. Crabs are also important prey species where they are available. On the west side of Kodiak Island, we see otters eating clams, scallops, crab, and octopus. Sea otters’ diets vary not only from one location to another and in response to available prey species, but also because individual otters have different food preferences, and a mother often passes on her fondness for certain foods to her pup.

A sea otter has a loose pouch of skin under each foreleg where it can store food collected on a dive. When the otter returns to the surface, it can rest on its back and leisurely retrieve one piece of food after another from its pouch. In addition to food, the sea otter also stores a rock in one of its pouches. The otter can use the rock underwater to pry loose mussels or other attached bivalves or to dislodge sea urchins wedged in crevices. When floating on the surface, the otter places the rock on its chest and pounds crabs, snails, clams, and other prey against the rock to break through the tough shells. Sea otters are one of the few animals other than humans known to use tools.

Sea otters are very efficient at finding and eating shellfish, and where large groups of sea otters reside, they reduce populations of abalones, clams, and sea urchins to the point where a commercial fishery for these species in the area is not viable. This competition between sea otters and fishermen creates a conflict which cannot be easily resolved by fish and wildlife managers.

Sea otters are considered a “Keystone” species, meaning they affect the ecosystem to a much greater degree than their numbers would suggest. Sea otters protect kelp forests off Northern California by eating herbivores such as sea urchins that graze on the kelp. In turn, the kelp forests provide food and cover for many other species of animals, and kelp forests play an important role in capturing carbon and reducing atmospheric carbon dioxide levels. Without sea otters, urchins over-graze the kelp, throwing the ecosystem out of balance.

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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. If you like audiobooks, check out her audiobook version of Murder Over Kodiak. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.

Mystery Newsletter

How Do Sea Otters Stay Warm?

October 28, 2018Kodiak Wildlife, Sea OtterAlaskan Sea Otters, How Do Sea Otters Stay Warm, Northern Sea Otter, Robin Barefield, sea otter, Sea Otters near Kodiak Islandadmin

Northern sea otters (Enhydra lutris kenyoni) are common in the waters surrounding Kodiak Island. Our summer guests love watching and photographing these cute, curious animals as we pass by them in our boat. Some otters lie placidly on their backs and watch us motor past, and others dive from the perceived danger we create. A few otters repeatedly twist and turn in the water or turn summersaults, and we laugh at their comical antics. The truth is, though, sea otters don’t turn summersaults because they are having fun; these movements have the much more practical application of keeping the animals warm.

A marine mammal must maintain a body temperature near 100° F (37.8° C), and in Alaska, where the water temperature drops as low as 35° F (1.67° C), keeping warm can be a challenge. Other marine mammals have a thick layer of blubber to insulate themselves from the cold, but sea otters have very little fat and depend mainly on their fur for insulation. Sea otters have the thickest fur of any animal, with 850,000 to one million hairs per square inch (up to 150,000 per square centimeter). It is their dense, beautiful fur that made them so valuable to fur traders in the 1700’s and 1800’s.

A sea otter’s fur consists of two layers. Long guard hairs form the outer layer, providing a protective coat to keep the underfur dry. The extremely dense underfur provides warmth, but for the fur to insulate efficiently, it must be clean, so sea otters spend a large portion of each day grooming and cleaning their fur.

In addition to cleaning his fur, an otter will somersault in the water and rub his body to trap air bubbles in his fur. These bubbles not only provide insulation but also help to keep his skin dry. An otter’s underfur ranges from brown to black, and the guard hairs vary from light brown to silver or black. Alaskan sea otters often have lighter fur on their heads, and the fur usually lightens as an otter gets older.

In addition to their warm fur, sea otters maintain their body heat by burning calories at a rapid rate. A sea otter’s metabolism is two to three times higher than the metabolism of a similar-sized land mammal. Because its metabolic rate is so high, a sea otter must eat 23 to 33 percent of its body weight each day. This means a fifty-pound otter will eat 11 to 16 lbs. (5 to 7.3 kg) of food every day.

Because very little fur covers an otter’s paws, they lose heat rapidly when submerged in cold water, otters conserve heat by keeping their forepaws out of the water and their hind flippers folded over their abdomens when resting and floating.

Since sea otters are dependent on their fur to keep them warm and insulated from the cold ocean water, and because they must continually groom their fur to maintain its insulating properties, they are extremely vulnerable to the effects of pollution. When oil or another pollutant soils an otter’s fur, the fur becomes matted, and it can no longer keep the animal warm. Matted fur can lead to hypothermia and death from exposure. When the otter tries to clean his fur to remove the pollutant, he ingests the toxin, which is also often fatal.

When the Exxon Valdez struck a reef in Prince William Sound in 1989 and spilled eleven million gallons of crude oil, nearly 1000 sea otter carcasses were recovered, and biologists estimated the actual number of sea otters killed by the oil spill was anywhere from 41% to 80% higher than the number of dead otters observed.

Sea otters have many interesting adaptations to a life spent in the ocean. In this post, I told you how much sea otters need to eat each day just to stay warm, and next week, I’ll write about what sea otters eat and how they catch and eat their prey.

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Mystery Newsletter

Sea Otters Part 2

February 14, 2016Kodiak Wildlife, Sea OtterAlaskan Sea Otters, Kodiak Island, Kodiak Wildlife, Sea Otter facts, Sea Ottersadmin

Sea otters are well adapted to their marine environment. Their nostrils and ears can close when diving, and they are able to change the refractive power of their lenses so they can see clearly in water as well as in air. The skeleton of a sea otter is loosely articulated and has no clavicle, allowing the animal a great deal of flexibility when swimming and grooming. A sea otter’s hind feet are flattened and webbed much like flippers, and the fifth digit on each foot is elongated, allowing the otter to swim more efficiently on its back. The front paws are short and have extendable claws and tough pads on the palms, enabling the otter to grip slippery prey, and the teeth are adapted for crushing hard-shelled invertebrates. Sea otters have large, lobulated kidneys that allow them to conserve water and maintain water balance while living in a saltwater environment, Their kidneys efficiently absorb water and eliminate excess salt in urea, a waste product more concentrated than sea water. Sea otters are very buoyant due to their large lungs, which are two-and-one-half times bigger than those of a similar-sized land mammal.

Sea otters are not particularly streamlined, and because of this, they are the slowest swimming of all marine mammals. Top speed for a sea otter is 5.6 mph (9 km/hr), but speeds of 2 to 3 mph (3.2 to 4.8 km/hr) are more common. Sea otters usually swim on their backs while paddling with their hind flippers, but when an otter needs to travel quickly, it swims on its stomach and undulates its entire body. Sea otters are graceful in the ocean, but they aren’t built to travel on land. It is rare to see a sea otter on land, but some like to haul out on rocks, and on Kodiak, we occasionally see sea otters resting on blocks of ice in the winter. When they do travel on land, they travel at a clumsy, rolling gait or run in a bounding motion.

Otters generally dive and feed in fairly shallow water, less than 60 ft.(18.3 m), and they normally only stay under water for one to two minutes, but they have been known to dive as deep as 330 ft. (100.58 m) and remain submerged for as long as four to five minutes. They are able to stay under water this long because of their large lungs that can store an abundant supply of oxygen, and because of their flexible ribs that allow their lungs to collapse under pressure.

A marine mammal must maintain a body temperature near 100° F (37.8° C), and in Alaska, where the water drops as low as 35° F (1.67° C), this can be a challenge. Other marine mammals have a thick layer of blubber to insulate themselves from the cold, but sea otters have very little fat and depend mainly on their fur to keep them warm. Sea otters have the thickest fur of any animal, with 850,000 to one million hairs per square inch (up to 150,000 per square centimeter). It is their dense, beautiful fur that made them so valuable to fur traders in the 1700’s and 1800’s.

The fur consists of two layers. Long guard hairs form the outer layer, and these provide a protective coat that keeps the underfur dry. It is this extremely dense underfur that keeps the otter warm, but to insulate efficiently, the fur must be clean, so sea otters spend a large portion of each day grooming and cleaning their fur.In addition to cleaning his fur, an otter will somersault in the water and rub his body to trap air bubbles in his fur. These bubbles not only provide insulation but also help to keep the skin dry. Since sea otters must have clean fur to stay warm, they are particularly susceptible to the ravages of an oil spill. If their fur becomes oiled, it loses its insulating properties. And when an otter tries to clean his oiled fur, he ingests the toxins from the oil.An otter’s underfur ranges from brown to black, with guard hairs that may be light brown, silver, or black. Alaskan sea otters often have lighter fur on their heads, and the fur usually lightens as an otter ages.

In addition to their warm fur, sea otters maintain their body heat by burning calories at a rapid rate. A sea otter’s metabolism is two to three times higher than that of a similar-sized land mammal. Because its metabolic rate is so high, a sea otter must eat 23 to 33 percent of its body weight each day. That means that a fifty-pound otter will eat 11 to 16 lbs. (5 to 7.3 kg) of food every day. Sea otters also maintain their body heat by keeping their forepaws out of the water and their hind flippers folded over their abdomens when resting and floating. An otter’s paws are covered by very little fur and lose heat rapidly when submerged in cold water.