Maze of a Walrus. Big tusks on
these friendly creatures. Maze starts in the upper left forner around
his right eye and exit of the maze is in the lower right corner right
past his blubber and right tusk. This maze goes with the maze
of
the
letter
W for the kids
book, "Learn To A Maze" Which uses mazes to teach kids the alphabet. By
Yonatan Frimer.
The walrus (Odobenus rosmarus)
is
a large flipperedmarine
mammal with a discontinuous circumpolar distribution in the Arctic
Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the
only living species in the Odobenidaefamily and Odobenusgenus. It
is subdivided into three subspecies:[1]
the Atlantic Walrus (O. rosmarus rosmarus) which lives
in the Atlantic Ocean, the Pacific Walrus (O.
rosmarus
divergens) which lives in the Pacific
Ocean, and O. rosmarus laptevi, which lives in the Laptev
Sea.
The walrus is immediately recognized by
its prominent tusks,
whiskers and great bulk. Adult Pacific males
can weigh up to 1,700 kilograms (3,700 lb)[3]
and, among pinnipeds, are exceeded in size only by the two
species of elephant seals.[4]
It resides primarily in shallow oceanic shelf habitat, spending a significant
proportion of its life on sea ice in pursuit of its preferred diet of benthicbivalve
mollusks. It is a relatively long-lived, social animal and is
considered a keystone species in Arctic marine ecosystems.
The walrus has played a prominent role in
the cultures of many indigenous Arctic
peoples, who have hunted the walrus for its meat, fat, skin, tusks
and bone.
In the 19th and early 20th centuries, the walrus was the object of
heavy commercial exploitation for blubber
and ivory and its numbers declined rapidly. Its
global population has since rebounded, though the Atlantic and Laptev
populations remain fragmented and at historically depressed levels.
O. rosmarus rosmarus O. rosmarus divergens O. rosmarus laptevi (debated)
Distribution
of
walrus
A walrus, labeled "Ros marus piscis", depicted in а 16th century
map of Scandinavia (the Carta Marina).
The origin of walrus has variously
been attributed to combinations of the Dutch words walvis ("whale") and ros
("horse")[5]
or wal ("shore") and reus ("giant").[6]
However, the most likely origin of the word is the Old
Norsehrossvalr, meaning "horse-whale", which was passed in
an inverted form to Dutch and the North-German dialects as walros
and Walross.[7]
The now archaic English word for walrus—morse—is
widely
supposed to have come from the Slavic.[8]
Thus морж (morž) in Russian, mursu in Finnish, moršâ in Saami, and morse
in French. Olaus
Magnus, who depicted the walrus in the carta
marina in 1539, first referred to it as the ros marus,
likely a Latinization of morž, and this was adopted by Linnaeus in the binomial nomenclature.[9]
The coincidental similarity between "morsus" and the Latin for "death" (mors)
and
"to bite" (mordere) supposedly contributed to the walrus'
reputation as a "terrible monster".[9]
The compound Odobenus comes from odous
(Greek for "tooth") and baino (Greek
for "walk"), based on walrus observations using their tusks to pull
themselves out of the water. The term divergens in Latin
means "turning apart", referring to the tusks.
Taxonomy and evolution
The walrus is a mammal in the orderCarnivora.
It
is the sole surviving member of the family Odobenidae, one of three lineages
in the suborderPinnipedia along with true seals (Phocidae) and eared seals (Otariidae). While there has been some debate
as to whether all three lineages are monophyletic, i.e. descended from a single
ancestor, or diphyletic, recent genetic
evidence suggests that all three descended from a caniform ancestor most closely related to
modern bears.[10]
Recent multigene analysis indicates that the odobenids and otariids
diverged from the phocids approximately 20–26 million years ago, while
the odobenids and the otariids separated 15–20 million years ago.[11][12]
Odobenidae was once a highly diverse and widespread family, including
at least twenty species in the Imagotariinae, Dusignathinae and
Odobeninae subfamilies.[13]
The key distinguishing feature was the development of a squirt/suction
feeding mechanism; tusks are a later feature specific to Odobeninae, of
which the modern walrus is the last remaining (relict)
species.
Two subspecies are commonly recognized:
the Atlantic Walrus, O. r. rosmarus (Linnaeus, 1758) and the
Pacific Walrus, O. r. divergens (Illiger, 1815). Fixed genetic
differences between the Atlantic and Pacific subspecies indicate very
restricted gene flow, but relatively recent separation, estimated at
500,000 and 785,000 years ago.[14]
These dates coincide with the fossil-derived hypothesis that the walrus
evolved from a tropical or sub-tropical ancestor that became isolated
in the Atlantic Ocean and gradually adapted to colder conditions in the
Arctic.[14]
From there, it presumably re-colonized the North Pacific during high
glaciation periods in the Pleistocene
via the Central American Seaway.[11]
An isolated population in the Laptev
Sea is considered by some, including Russian biologists and the
canonical Mammal Species of the World,[1]
to be a third subspecies, O. r. laptevi (Chapskii, 1940), and
is managed as such in Russia.[15]
Where the subspecies separation is not accepted, whether to consider it
a subpopulation of the Atlantic or Pacific subspecies remains under
debate.[4][16]
Young male Pacific Walruses on Cape Pierce in Alaska.
Note the variation in the curvature and orientation of the tusks and
the bumpy skin (bosses), typical of males.
Anatomy
Walrus using its tusks to hang on breathing hole in the ice near St. Lawrence Island, Bering Sea
Skeleton
While isolated Pacific males can weigh as
much as 2,000 kg (4,400 lb), most weigh between 800 and 1,800 kg
(1,800 and 4,000 lb). Females weigh about two-thirds as much, and the
Atlantic subspecies weighs about 90% as much as the Pacific subspecies.[4]
The Atlantic Walrus also tends to have relatively shorter tusks and
somewhat more flattened snout. It is the second largest pinniped, after the elephant seals.
The walrus' body shape shares features
with both sea lions (eared seals: Otariidae) and seals (true
seals: Phocidae). As with otariids, it can turn its rear flippers
forward and move on all fours; however, its swimming technique is more
like that of true seals, relying less on flippers and more on sinuous
whole body movements.[4]
Also like phocids, it lacks external ears.
Tusks and dentition
The most prominent feature of the walrus
is the long tusks. These are elongated canines, which are present in both sexes and
can reach a length of 1 metre (3 ft 3 in) and weigh
up to 5.4 kilograms (12 lb).[17]
Tusks are slightly longer and thicker among males, who use them for
fighting, dominance and display; the strongest males with the largest
tusks typically dominate social groups. Tusks are also used to form and
maintain holes in the ice and aid the walrus in climbing out of water
onto ice.[18]
It was previously assumed that tusks were used to dig out prey from the
seabed, but analyses of abrasion patterns on the tusks indicate that
they are dragged through the sediment while the upper edge of the snout
is used for digging.[19]
While the dentition of walruses is highly variable, they
generally have relatively few teeth other than the tusks. The maximal
number of teeth is 38 with dentition formula: ,
but
over half of the teeth are rudimentary and occur with less than 50%
frequency, such that a typical dentition includes only 18 teeth [4]
Vibrissae
Surrounding the tusks is a broad mat of
stiff bristles ('mystacial vibrissae'), giving the walrus a
characteristic whiskered appearance. There can be 400 to 700 vibrissae
in 13 to 15 rows reaching 30 centimetres (12 in) in length, though
in the wild they are often worn to a much shorter length due to
constant use in foraging.[20]
The vibrissae are attached to muscles and are supplied with blood and
nerves making them a highly sensitive organ capable of differentiating
shapes 3 mm (0.12 in) thick and 2 mm (0.079 in) wide.[20]
Skin
Aside from the vibrissae, the walrus is
sparsely covered with fur and appears bald. Its skin is highly wrinkled
and thick, up to 10 cm (3.9 in) around the neck and shoulders of
males. The blubber layer beneath is up to 15 cm (5.9 in)
thick. Young walruses are deep brown and grow paler and more
cinnamon-colored as they age. Old males, in particular, become nearly
pink. Because skin blood vessels constrict in cold water, the walrus
can appear almost white when swimming. As a secondary
sexual characteristic, males also acquire significant nodules,
called bosses, particularly around the neck and shoulders.[18]
The walrus has an air sac under its throat which acts like a
floatation bubble and allows it to bob vertically in the water and
sleep. The males possess a large baculum
(penis bone), up to 63 cm (25 in) in length, the largest of any
land mammal, both in absolute size and relative to body size.[4]
Life history
Walruses fighting
Reproduction
Walruses live to about 20–30 years old in
the wild.[21]
The males reach sexual maturity as early as 7 years, but do not
typically mate until fully developed around 15 years of age.[4]
They rut from January through April, decreasing their food intake
dramatically. The females begin ovulating as soon as 4–6 years old.[4]
The females are polyestrous, coming into
heat in late summer and also around February, yet the males are fertile
only around February; the potential fertility of this second period is
unknown. Breeding occurs from January to March, peaking in February.
Males aggregate in the water around ice-bound groups of estrous females
and engage in competitive vocal displays.[22]
The females join them and copulate in the water.[18]
Gestation
lasts 15 to 16 months. The first 3 to 4 months are spent with the blastula
in suspended development before it implants itself in the placenta.
This strategy of delayed implantation,
common
among pinnipeds, presumably evolved to optimize both the mating
season and the birthing season, determined by ecological conditions
that promote newborn survival.[23]
Calves are born during the spring migration, from April to June. They
weigh 45–75 kg (99–170 lb) at birth and are able to swim. The mothers
nurse for over a year before weaning, but the young can spend up to 3
to 5 years with the mothers.[18]
Because ovulation is suppressed until the calf is weaned, females give
birth at most every two years, leaving the walrus with the lowest
reproductive rate of any pinniped.[24]
Migration
The rest of the year (late summer and
fall) the walrus tends to form massive aggregations of tens of
thousands of individuals on rocky beaches or outcrops. The migration
between the ice and the beach can be long distance and dramatic. In
late spring and summer, for example, several hundred thousand Pacific
Walruses migrate from the Bering sea into the Chukchi sea through the
relatively narrow Bering Strait.[18]
Ecology
Range and habitat
Walrus colony
The majority of the Pacific Walrus
population summers north of the Bering
Strait in the Chukchi Sea along the north shore of eastern Siberia,
around
Wrangel Island, in the Beaufort
Sea along the north shore of Alaska,
and in the waters between those locations. Smaller numbers of males
summer in the Gulf of Anadyr on the south shore of
Siberia's Chukchi Peninsula and in Bristol Bay off
the south shore of southern Alaska west of the Alaska Peninsula. In the spring and fall
they congregate throughout the Bering Strait, reaching from the west
shores of Alaska to the Gulf of Anadyr. They winter in the Bering Sea
along the eastern shore of Siberia south to the northern part of the Kamchatka Peninsula, and along
Alaska's southern shore.[4]
A 28,000 year old fossil walrus specimen was dredged out of San Francisco Bay, indicating that the
Pacific Walrus ranged far south during the last ice age.[25]
The much smaller Atlantic population
ranges from the Canadian Arctic, Greenland,
Svalbard
and the western portion of the Russian Arctic. There are eight presumed
sub-populations based largely on geographical distribution and movement
data, five to the west of Greenland and three to the east.[26]
The Atlantic Walrus once ranged south to Cape Cod
and occurred in large numbers in the Gulf of St. Lawrence.
In
April 2006, the Canadian Species at Risk Act listed the Northwest
Atlantic Walrus population (Québec, New
Brunswick, Nova Scotia, Newfoundland and Labrador) as
being extirpated in Canada.[27]
The isolated Laptev population is confined
year-round to the central and western regions of the Laptev
Sea, the easternmost regions of the Kara Sea,
and
the westernmost regions of the East Siberian Sea. Current populations
are estimated to be between 5,000 and 10,000 individuals.[28]
Their limited diving ability brings them
to depend on shallow waters (and appropriate nearby ice coverage) to
enable them to reach their preferred benthic prey.
Population
There were roughly 200,000 Pacific
Walruses according to the most recent (1990) census-based estimate.[29][30]
The Atlantic Walrus was nearly eradicated
by commercial harvest and has a much smaller population. Good estimates
are difficult to obtain, but the total population is probably below
20,000.[31][32]
Walruses prefer shallow shelf regions and forage primarily on
the sea floor, often from sea ice platforms.[4]
They are not particularly deep divers compared to other pinnipeds: the
deepest recorded dives are around 80 metres (260 ft). They can
remain submerged for as long as half an hour.[33]
The walrus has a diverse and opportunistic
diet, feeding on more than 60 genera of marine organisms including shrimp, crabs, tube
worms, soft corals, tunicates,
sea cucumbers, various mollusks, and even parts of other pinnipeds.[34]
However, it prefers benthic bivalve mollusks, especially clams, for
which it forages by grazing along the sea bottom, searching and
identifying prey with its sensitive vibrissae and clearing the murky bottoms with
jets of water and active flipper movements.[35]
The walrus sucks the meat out by sealing its powerful lips to the
organism and withdrawing its tongue, piston-like, rapidly into its
mouth, creating a vacuum. The walrus palate is uniquely vaulted,
enabling effective suction.
Aside from the large numbers of organisms
actually consumed by the walrus, its foraging has a large peripheral
impact on benthic communities. It disturbs (bioturbates)
the
sea floor, releasing nutrients into the water column, encouraging
mixing and movement of many organisms and increasing the patchiness of
the benthos.[19]
Seal tissue has been observed in fairly
significant proportion of walrus stomachs in the Pacific, but the
importance of seals in the walrus diet is under debate.[36]
There have been rare documented incidents of predation on seabirds,
particularly the Brünnich's
GuillemotUria lomvia.[37]
Predation
Due to its great size, the walrus has only
two natural predators: the orca and the polar
bear. It does not, however, comprise a significant component of
either predator's diet. The polar bear hunts the walrus by rushing at
beached aggregations and consuming individuals that are crushed or
wounded in the sudden exodus, typically younger or infirm animals.[38]
However, even an injured walrus is a formidable opponent for a polar
bear, and direct attacks are rare.
Walrus tusk engraving made by Chukchi artisans depicting polar bears
attacking walruses. On display in the Magadan Regional Museum, Magadan,
Russia
In the 18th and 19th centuries, the walrus
was heavily exploited by American and European sealers
and whalers,
leading
to the near extirpation of the Atlantic population.[39]
Commercial walrus harvesting is now outlawed throughout its range,
although Chukchi, Yupik and Inuit
peoples,[40]
continue to kill small numbers towards the end of each summer.
Traditional hunters used all parts of the
walrus.[41]
The meat, often preserved, is an important winter nutrition source; the
flippers are fermented and stored as a delicacy until spring; tusks and
bone were historically used for tools as well as material for
handicrafts; the oil was rendered for warmth and light; the tough hide
made rope and house and boat coverings; the intestines and gut linings
made waterproof parkas; etc. While some of these uses have faded with
access to alternative technologies, walrus meat remains an important
part of local diets,[42]
and tusk carving and engraving remain a vital art form.
Walrus hunts are regulated by resource
managers in Russia, the United
States, Canada and Denmark
and representatives of the respective hunting communities. An estimated
4–7,000 Pacific Walruses are harvested in Alaska
and Russia, including a significant portion (approx. 42%) of struck and
lost animals.[43]
Several hundred are removed annually around Greenland.[44]
The sustainability of these levels of harvest is difficult to determine
given uncertain population estimates and parameters such as fecundity
and mortality.
The effects of global climate change
is another element of concern. The extent and thickness of the pack ice
has reached unusually low levels in several recent years. The walrus
relies on this ice while giving birth and aggregating in the
reproductive period. Thinner pack ice over the Bering Sea has reduced
the amount of resting habitat near optimal feeding grounds. This more
widely separates lactating females from their calves, increasing
nutritional stress for the young and lower reproductive rates.[45]
Reduced coastal sea ice has also been implicated in the increase of
stampeding deaths crowding the shorelines of the Chukchi
Sea between eastern Russia and western Alaska.[46][47]
However, there is insufficient climate data to make reliable
predictions on population trends.[48]
Currently, two of the three walrus
subspecies are listed as "least-concern" by the IUCN, while the third is "data deficient".[2]
The Pacific Walrus is not listed as "depleted" according to the Marine Mammal Protection Act
nor as "threatened" or "endangered" under the Endangered Species Act. The Russian
Atlantic and Laptev Sea populations are classified as Category 2
(decreasing) and Category 3 (rare) in the Russian Red Book.[28]
Global trade in walrus ivory is restricted according to a CITES
Appendix 3 listing.
The walrus plays an important role in the religion
and folklore
of many Arctic
peoples. Skin and bone are used in some ceremonies and the animal
appears frequently in legends. For example, in a Chukchi version of the widespread myth of the Raven, in which Raven
recovers the sun and the moon from an evil spirit by seducing his
daughter, the angry father throws the daughter from a high cliff and,
as she drops into the water, she turns into a walrus — possibly the
original walrus. According to various legends, the tusks are formed
either by the trails of mucus from the weeping girl or her long braids.[49]
This myth is possibly related to the Chukchi myth of the old
walrus-headed woman who rules the bottom of the sea, who is in turn
linked to the Inuit goddess Sedna. Both in Chukotka and Alaska,
the aurora borealis is
believed to be a special world inhabited by those who died by violence,
the changing rays representing deceased souls playing ball with a
walrus head.[49][50]
Because of its distinctive appearance,
great bulk and immediately recognizable whiskers and tusks, the walrus
also appears in the popular cultures of peoples with little direct
experience with the animal, particularly in English children's
literature. Perhaps its best known appearance is in Lewis
Carroll's whimsical poem The Walrus and the Carpenter
that appears in his 1871 book Through the Looking-Glass.
In the poem, the eponymousanti-heroes use trickery to consume a great
number of oysters.
Although
Carroll accurately portrays the biological walrus's appetite
for bivalve mollusks, oysters, primarily nearshore and intertidal inhabitants, in fact comprise an
insignificant portion of its diet, even in captivity.[51]
Another appearance of the walrus in
literature is in the story The White Seal in Rudyard Kipling's The Jungle Book, where it is the "old
Sea Vitch—the big, ugly, bloated, pimpled, fat-necked, long-tusked
walrus of the North Pacific, who has no manners except when he is asleep".[52]
^ ab
Lowry, L., Kovacs, K. & Burkanov, V. (IUCN SSC Pinniped Specialist
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IUCN 2008. IUCN Red List of Threatened
Species. Downloaded on 22 March 2009. Database entry includes a brief
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^Lento, G.M., Hickson, R.E.,
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^ abArnason U, Gullberg A, Janke A, et
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^Kohno, N. (2006). "A new Miocene Odobenid
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^ abHoelzel, A. R. (Ed.), ed (2002). Marine
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^Born, E. W., Gjertz, I., and Reeves, R. R.
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^Berta, A. and J. L. Sumich (1999). Marine
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^ abcdeFay, F. H. (1982). "Ecology and
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^ abRay, C., McCormick-Ray, J., Berg,
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^ abKastelein, R.A., Stevens, S., &
Mosterd, P. (1990). "The sensitivity of the vibrissae of a Pacific
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^S. N. Nowicki, I. Stirling, B. Sjare (1997).
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^Sandell, M. (1990). "The Evolution of
Seasonal Delayed Implantation". The Quarterly Review of Biology65 (1): 23–42. doi:10.1086/416583. PMID2186428.
^Born, E. W., Andersen, L. W., Gjertz, I. and
Wiig, Ø (2001). "A review of the genetic relationships of
Atlantic walrus (Odobenus rosmarus rosmarus) east and west of
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^Gilbert, J.R., G.A. Fedoseev, D. Seagars, E.
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^
[NAMMCO] North Atlantic Marine Mammal Commission. 1995. Report of the
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^Schreer, J. F., K. M. Kovacs, and R. J.
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^Sheffield G., Fay F. H., Feder H., Kelly B.
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^Lowry, L.F. and Frost, K.J. (1981). "Feeding and
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^Mallory, M. L., Woo, K., Gaston, A. J.,
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^Garlich-Miller, J.G. and D.M. Burn (1997).
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Meet the audacious ice swimmers — or “walruses” as they
like to be known — of Serebryanny Bor (literally “Silver Pinewood”), a
picturesque expanse of white ...
Let's just set aside concerns that this climate change will
soon endanger the lives of thousands of ringed seals and Pacific walruses
as they lose critical ...
,
but
over half of the teeth are rudimentary and occur with less than 50%
frequency, such that a typical dentition includes only 18 teeth 
