Tag Archives: sea otter

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 3

February 21, 2016UncategorizedNorthern Sea Otter, sea otter, Sea otter biology, Sea otters in Alaska, Sea Otters near Kodiak Island, Wildlife of Kodiak Islandadmin

A sea otter has a loose pouch of skin under each foreleg where it can store food as it’s collected. 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 may use the rock under water 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.

Mating can occur at any time of the year for sea otters, and while the young may be born in any season, most pups in Alaska are born in the spring. As with bears, when a sea otter becomes pregnant, the implantation and development of the embryo often stops, and the embryo may not implant for several months. Scientists believe the purpose of delayed implantation in sea otters is to allow for the birth of pups when environmental conditions and food supplies are most favorable. Sea otters are pregnant for four months, but because the length of the delayed implantation varies so greatly, the gestation period may last from four to twelve months.

Sea otter mothers are normally very attentive, affectionate, and protective of their pups. A pup spends most of its time riding on its mother’s belly, and even pups six-months of age or older and nearly as large as their mother will climb on her stomach as she appears to struggle to keep her head above water.

In addition to cradling her pup on her chest to keep him warm, a mother meticulously grooms her pup’s fur until the pup is three to four months old and able to groom himself. At this age, the pup is also able to swim on his back and dive with ease. The mother teaches the pup how to catch and eat prey, and by the time the pup is six months old, he can capture and break open his own prey. Sea otter pups remain with their mothers anywhere from three to twelve months.

Sea otters often float together in large groups called rafts. Except for territorial males who rest with female groups, most rafts are comprised of individuals of the same sex, and mothers with pups often rest together in nursery groups. Rafts usually consist of between ten and more than one-hundred otters, but in Alaska, rafts with 2000 individuals have been reported.

Sea otters are considered a “Keystone” species, meaning that they effect the ecosystem to a much greater degree than their numbers would suggest. Sea otters protect kelp forests 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.

Sea Otters

February 7, 2016Kodiak Wildlife, Sea OtterKodiak Island wildlife, sea otter, Sea otters in Alaska, Sea Otters near Kodiak Islandadmin

Sea otters evoke strong emotions in humans. Most of us can’t help but say, “Ahhhh!” when we see a cute furry otter floating on its back or looking at us in surprise, front flippers held high in the air. Watching a baby sea otter sitting on its mother’s stomach, or hearing one break open a clam on a rock makes most of us smile. Many fishermen, though, are not fond of sea otters and for a good reason. Sea otters are so efficient at finding and eating shellfish that they are able to reduce populations of abalones, clams, and sea urchins to the point where a commercial fishery for these species is not viable in areas with large sea otter populations. In this post and my next two posts, I’ll discuss sea otters and their fascinating biology and behavior.

While sea otters are the second smallest marine mammal, they are the largest members of the mustelid family, which also includes freshwater otters, weasels, minks, skunks and badgers. Sea otters may weigh as much as 100 lbs (45.5 kg). The average adult California female weighs 44 lbs. (20 kg), and the average male weighs 64 lbs. (29 kg). In Alaska, the average adult female is 4 ft. (1.2 meters) long and weighs 60 lbs. (27.3 kg), while the average adult male is 5 ft. (1.5 meters) long and weighs 70 lbs. (31.8 kg).

Sea otters are the only mustelid in the genus Enhydra, and they are significantly different from all other mustelids. Sea otters are one of nine to thirteen (taxonomists disagree on the exact number) species of otters found around the world. Except for sea otters and the endangered species of marine otters, all other otters live primarily in freshwater, although river otters (Lutra canadensis) travel freely between rivers and the ocean, and on Kodiak, it is common to see river otters swimming near shore in the ocean. River otters and sea otters resemble each other, but sea otters are larger and weigh two to three times more than river otters. Sea otters have adapted to a life in the ocean with hind feet that are webbed to the tips of their toes and resemble flippers. River otters also have webbed feet, but they are small, making it easier for river otters to move on land, while sea otters are very clumsy out of water. A sea otter’s tail is flat and looks like a paddle, while a river otter has a long, round tail that tapers to a point. The claws in the forepaws of a sea otter can be extended, but those of a river otter cannot. River otters swim on their stomachs, and although sea otters can also swim on their stomachs, they usually swim on their backs while paddling with their hind flippers. River otters give birth to litters of up to four pups, but sea otters, like other marine mammals, usually only give birth to a single pup.

There are three subspecies of sea otters. Enhydra lutris lutris ranges from the Kuril Islands to the Commander Islands in the western Pacific Ocean. The sea otters in this subspecies are the largest and have a wide skull and short nasal bones. The Southern sea otters, or the California sea otters as they are commonly called (Enhydra lutris nereis), are found off the coast of central California. Sea otters in this group are smaller and have a narrower skull with a long rostrum and small teeth. The vast majority of sea otters belong to the subspecies Enhydra lutris kenyoni, the Northern sea otters. This subspecies ranges from the Aleutian Islands to British Columbia, Washington, and northern Oregon.

Before the 1700’s, an estimated 150,000 to 300,000 sea otters inhabited the area from northern Japan to the Alaska Peninsula and along the Pacific coast of North America to southern California. Between 1741 and 1911 when sea otters were aggressively harvested for their luxurious furs, the population dropped to only 1000 to 2000 animals, and they had been eliminated from much of their original range. Many biologists believed the population was headed toward extinction. In 1911, the International Fur Seal Treaty was signed by the U.S., Russia, Great Britain, and Japan, stopping the commercial hunting of sea otters, and slowly, their numbers began to increase.Sea otters began re-colonizing much of their former range and were reintroduced to other areas. Sea otters now occupy about two-thirds of their historical range.

Counts between 2004 and 2007 estimate the worldwide sea otter population at approximately 107,000 animals. Sea otter populations are considered stable in most areas, although California populations have plateaued or slightly decreased, and there has been a drastic decline in sea otter numbers in southwest Alaska, from Kodiak Island through the western Aleutian Islands. This area once contained more than half of the world’s sea otters, but the population has declined by at least 55 to 67 percent since the mid 1980’s, and in 2005, the U.S. Fish and Wildlife Service listed this distinct population segment as Threatened under the Endangered Species Act. In 1973, the otter population in Alaska was estimated at between 100,000 and 125,000 animals, but by 2006, the population had fallen to approximately 73,000 animals, mainly due to declines in the Southwest Alaska District Population Segment. The cause of this decline is unclear, but evidence suggests that it may be due to increased predation by killer whales.

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Mid-Summer 2015

August 23, 2015Fin Whale, Humpback Whale, Kodiak Bear, Sea OtterBear watching, humpback whale, Kodiak Bear, Kodiak Island, Kodiak tourism, Munsey's Bear Camp, sea otteradmin

Mid-Summer 2015 is the post I wrote for our Munsey’s Bear Camp website.

I love watching our guests relax as they transition from their stress-filled lives into our peaceful, wild world. When they first step off the floatplane, they are often quiet and perhaps even a little wary. They’ve just flown forty-five minutes into the heart of the Kodiak National Wildlife Refuge, and there are no roads or stores here. There’s just a small lodge and a few boats.

We feed them lunch, Mike explains what they will be doing for the next few days, and we tell them to meet us at the dock in twenty minutes for their first-afternoon cruise on our 43-ft. boat. They laugh at the sea otters and harbor seals and snap photos of bald eagles and other wildlife, but most remain quiet, and separate groups keep to themselves.

On the first full day, we go either bear viewing or fishing, and by that evening, I begin to see the first signs of relaxation, as our guests step out of their lives for a few days and into a world that revolves around tides and wild animals. They ask us questions about the wildlife they’ve seen, tell us about their families, and describe other travel adventures they have had. They linger for a few minutes after dinner, discussing the day’s events with their fellow adventures.

By the fourth day, the mood on the boat is often raucous. These strangers, who on day one traded only polite comments, are now teasing each other and sharing photos and e-mail addresses. They sigh the last morning when they step off our boat for the final time. They complain that the week flew by too quickly and vow to return again soon.

We’ve had beautiful weather so far this summer, and we’ve enjoyed great whale watching. At times, we’ve been surrounded by fin whales, and one of the highlights of the summer was when a humpback breached several times right in front of us! Halibut fishing has been very good, and we’ve had some of the best salmon fishing we can remember. Pink salmon swarmed into Brown’s Lagoon in July, and we had non-stop action. Meanwhile, large schools of silver salmon filled the bay. The run was a month early, and it is likely that the early salmon were headed elsewhere and just stopped in Uyak Bay to feast on the large schools of herring and other small fish that have been so abundant this summer. The rich food base of krill and small schooling fish is also undoubtedly why we’ve had so many whales in the bay.

Due to our warm weather, we’ve had another bumper crop of berries this summer, and the bears are torn between catching salmon and feeding on berries. Bears are much more plentiful than they were the first half of last summer, but we are sometimes frustrated as we wait for them to lose interest in berries and concentrate on salmon. The rich and plentiful food source of berries and salmon the last few summers has provided great nutrition for the bears, and we’ve seen numerous groups of sows and cubs this summer.

On the home front, Mary Schwarzhans is again wowing our guests with her creative and delicious meals, and we are thrilled that Mary’s sister, Emma, is also working for us this summer. The two of them make our lives much easier and more pleasant, and our guests tell us that even if we didn’t have spectacular wildlife and fishing here, they would return to Munsey’s Bear Camp just for the food. I suspect that stepping out of their lives and truly relaxing for a few days might be another reason to return.