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.
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