Alaska Marine Mammals

A marine mammal is defined as any mammal that lives part or all of its life in a marine environment and obtains its food there.  The only exception is for river dolphins and a few seals, whom are considered marine mammals despite the fact that they live in freshwater rather than a marine (saltwater ocean) environment.  Marine mammals include whales, dolphins, porpoises, pinnipeds (seals, sea lions, and walruses), sirenians (manatees and dugongs), sea otters and polar bears.

Marine Mammal Protection Act  (MMPA):  The MMPA was enacted on October 21, 1972 and has since protected all marine mammals in US waters.  The purpose of the MMPA is to necessitate conservation of all marine mammals, many of which were heavily hunted and populations extremely depeleted in earlier decades. Under the MMPA marine mammals may not be hunted, harassed, hunted or killed in the US.  There are exceptions to the act, which allow “taking” of the animals by Alaskan natives, as well as for scientific and educational purposes.  Nonetheless, all marine mammals are federally protected by an invisible boundary and all those who want to observe the animals in the wild ought to do so respectfully.

Common name:  Harbor seal  Scientific name:  Phoca vitulina   One of the most distinctive physical characteristics used to differentiate a seal from a sea lion is that seals do not have external ears, whereas sea lions do.  Harbor seals are common in Alaskan waters, either seen at the surface silently taking a breath of air and peering around, hauling out onto beaches, or hiding from predators on glacial icebergs.  They are one of the most widely distributed  pinnipeds  worldwide.  Harbor seals have distinctive spotting on their grey fur coat.  They are generalist feeders, meaning they eat whatever is available.  Their food sources may range from fish, to squid, and crustaceans.  An accurate population count is not known, but their estimated numbers suggest that they are  a species of least concernwhen it comes to protection.

Common name:  Spotted seal  Scientific name:  Phoca largha   Spotted seals are a  sibling species  to harbor seals.  The name sibling species refers to two separate species who look nearly identical to one another.  The seal species' ranges overlap in the north Pacific, but spotted seals are only present north of the Bering Sea in Alaska.  The only way in which to differentiate the species in areas of overlap are by contrasting behavioral characteristics.  While spotted seals give birth on sea ice, and are typically observed individually or in small groups of up to three, harbor seals normally birth on glacial ice or land, and in large haul-out groups.  The exception to this rule is in Bristol Bay where spotted seals haul-out on land, and only very experienced observers can distinguish between the species based on behavioral and skull shape differences.  Young spotted seals have been noted to feed upon small crustaceans, and eventually expand their diet to fish and octopus.

Common name:   Ringed seal  Scientific name:  Pusa hispida  Ringed seals also resemble harbor and spotted seals, but are plumper with smaller heads.  The dark spots on their fur coat typically have white rings encircling them, hence their name.  Ringed seals are found in the North Pacific,their range beginning in the Bering Sea and expanding northwards.  The ringed seals also have unique breeding grounds, birthing only on  fast ice, which is grounded sea ice.  Ringed seals are  opportunistic  feeders, with over 72 species in their diet.  Two  subspecies  of ringed seals are isolated in freshwater, landlocked lakes in Russia.  Marine mammals whom reside solely in freshwater exist, and are an exception to the definition provided of a marine mammal.  Native peoples have been harvesting ringed seals for sustenance for thousands of years.  Ringed seal subspecies range from endangered to subspecies of least concern for extinction.

Common name:  Ribbon seal  Scientific name:  Histriophoca fasciata  Male ribbon seals have an exhuberant black and white banding pattern around their bodies.  This patterning exists on females as well, but in more discreet grey colors.  Ribbon seals are slender compared to most seals found in the far north.  Most necessitate a thick blubberous coat to keep warm in cold Arctic waters.  Ribbon seals and spotted seals have similar ranges from the Bering Sea and expanding northwards.  Ribbon seals are a favorite food of polar bears.  The seals maintain breathing holes in sea ice where polar bears wait to feed upon them.

Common seal:   Bearded seal  Scientific name:  Erignathus barbatus  Bearded seals are characterized by their large elongated bodies and small head size.  As with many other Arctic seals, their range begins in the Bering Sea.  Bearded seals give birth on sea ice in the spring, and follow the melting ice northwards in the summer as the ice melts.  As ice advances in the fall, they migrate south again.  Their migrations follow the natural fluctuations in sea ice.  Other than mother and recently born pups, bearded seals are extremely solitary and rarely seen in groups.  The animals always seem to be on guard, just a slip away from the water when hauled out on ice.  Compared to many other seals, this species lives in quite shallow waters.  Their diet consists of bottom dwelling species and their predators are killer whales, polar bears, and humans.

Common name:  Northern Elephant seal  Scientific name:  Mirounga angustirostrisNorthern elephant seals are an example of an extremely  sexually dimorphic  seal species.  Sexual dimorphism refers to unique physical characteristics between sexes of the same species.  Male elephant seals are immense in size with distinct long noses resembling an elephant's trunk (although their noses not quite as long!) and females are much smaller.  Scars become common on males, developing as males battle with others to keep their harem, or large groups of females with whom they mate with.  Male fights, noise, and displays are common on the mating grounds.  Breeding grounds occur from Baja California to southern Oregon.  Northern elephant seals undergo a long migration twice a year from their northern feeding grounds in Alaskan waters to their southern breeding and molting  (fur shedding from the previous winter) grounds.  Elephant seals travel between the north where they feed extensively and southern haul-out sights where they are fasting.  Male elephant seals tend to travel farther north when feeding than females do, and hence are most common in Alaskan waters.

Common name:  Steller sea lion  Scientific name:  Eumetopias jubatus
Steller sea lions exhibit sexual dimorphism as well.  Similarly to elephant seals, male stellers grow much larger than females.  The male’s large size is extremely beneficial to him because males form territorial groups of females when mating.  The bigger the sea lion, the more females one male can mate with, and thus the greater the likelihood of spreading his genes unto the next generation.  Steller sea lions are the largest of all sea lion species.  In addition to sea lions’ distinguishing external ears that seals do not have, sea lions also have rotating hind limbs that allow them to walk on land, whereas seals must wiggle rather than walk.  Sea lions are only present in the Pacific Ocean, but seals can be found in oceans worldwide.  The western Alaskan Steller sea lion stock is endangered  due to a sharp population decrease in the last few decades.  The reason for the decline is unknown, but may be related to reduction of food sources due to commercial fishing, global warming, as well as native harvesting of the marine mammals.  They can be found across most Alaskan waters.

Common name:  Northern fur seal  Scientific name:  Callorhinus ursinus  Northern fur seals are yet another example of sexually dimorphic species, males growing to more than four times the weight of females.  Although named a seal, these animals are actually more closely related to sea lions than seals, and thus have external ears.  The large males may also be distinguished by their hairy manes.  Females time the arrival to their birthing grounds perfectly, and typically give birth just one day after they have arrived to a  haul-out site.  This allows for efficient birthing, mating, and foraging soon after giving birth.  Mothers visit their newborn pups to nurse 8-12 times, after which the young quickly become independent.  Northern fur seals spend an immense amount of time at sea compared to many of their relatives.  The seals were commercially harvested until 1984 so their numbers have declined immensely.  Even with present marine mammal protections, their populations are diminishing and as a result they are considered a vulnerable species.  While they inhabit much of Alaska’s waters, the best place to see them is on their breeding grounds in the  Pribilof Islands, located in the Bering Sea.

Common name:  Harbor porpoise  Scientific name:  Phocoena phocoena  Harbor porpoises are distributed in oceans worldwide and are common in Alaskan waters.  They may be confused with another common porpoise, the Dall’s porpoise, but are easily distinguishable by a few qualities.  Firstly, harbor porpoises are completely grey, whereas Dall’s porpoises have white patches on their backs.  Typically harbor porpoises are seen individually, in pairs, or small groups, but Dall’s porpoises often travel in large schools.  Harbor porpoises inhabit shallow waters, are shy and rarely approach boats. Dall’s porpoise contrarily are quite friendly, curious and often approach boats.  Harbor porpoises’ greatest threats include killer whales and humans.  They are sometimes trapped as by-catch in fishing nets, are affected by marine pollution and boat traffic, and thus are presently considered a vulnerable species.

Common name:  Pacific white-sided dolphin  Scientific name:  Lagenorhynchus obliquidens  Pacific white-sided dolphins are the only of its dolphin type in Alaskan waters.  While killer whales are also a member of the dolphin family, the two have distinct  genera.  Dolphins and porpoises can be differentiated by a few characteristics.  Dolphins have a curved dorsal fine while porpoises have a triangular one.  Dolphins also have pointy teeth and a beak while porpoises have flat teeth and no beak.  Pacific white-sided dolphins have dark grey bodies, a light patch on their dorsal fins and light stripes on the their sides.  Dolphins are highly social and are often found in large schools.  The species can be found throughout the Pacific northwest to the south Bering sea.  They can inhabit deep, offshore waters as well shallower coastal ones.

Common name:  Walrus  Scientific name:  Odobenus rosmarus   The most distinguishing characteristic of a walrus is its large tusks, present in both males and females.  A male has longer tusks, suggesting that they are important in mating displays and aggressive battles.  The tusks are also used for movement onto ice flow from water.  Most walrus coloration ranges between yellow to reddish-brown.  After spending lengthy periods of time in cold water, their coloring fades to grey due to reduced blood flow to the animal’s outer skin layer.  In warm conditions walruses transform to a pinkish color, due to increased blood flow towards the periphery of the skin, allowing absorption of this warmth.  The animals have a thick blubber layer to allow for thermoregulation in the cold waters in which they live.  Walruses live in the far northern waters of Alaska, beginning in the Bering Sea and ranging northward to the Arctic.

Common name:  Polar bear  Scientific name:  Ursus maritimus  Polar bears are found only in the very far north of Alaska in the Arctic Ocean.  Their range typically correlates with sea ice allowing them rest after swimming. Polar bears are likely the most recent marine mammal to have evolved from their large grizzly bear relatives.  They have adapted to their marine environment well and have partially webbed claws for swimming.  They have also adapted hollow hairs to allow heat storage in cold water.  Polar bears are typically solitary animals, but tend to congregate in areas with high ringed seal densities.  They rarely hunt while in the ocean, but rather are seen collecting around ringed seal breathing holes in ice.  Some polar bears who don’t have access to sea ice during the summer months fast for months, but most feed year round.  Polar bears may spend time on land, but typically occupy sea ice when it is available.  Due to their reliance upon ice, polar bears are the first species to be listed as endangered due to the causes of global warming.

Common name:  Sea otter   Scientific name:  Enhydra lutris  Sea otters are indeed considered marine mammals, as they spend nearly all of their life, mate, and eat in the ocean.  Sea otters are unique marine mammals in that they have no blubber to keep themselves warm in cold northern waters.  Rather, they have the densest fur coat of any animal, with more that 100,000 hairs per square centimeter.  Otters may be seen from the Southeast Alaskan coast through the Aleutian Islands.  They are common surrounding coastlines and islands, rather than in open ocean.  Sea otters may be observed individually or in a groups called rafts.  Otters are most often seen at the water’s surface floating on their backs.  Recent studies suggest that sea otters are a very important part of kelp forest ecosystems, being a top predator in them.  Sea otters feast upon sea urchins, whom consume kelp.  In places where sea otter populations were depleted during the fur trade areas called “urchin barrens” are now present, where the sea bottom is mostly devoid of life other than urchins.  A diverse and healthy ecosystem seems to necessitate both sea otters and an abundance of kelp.