Pinnipeds (from Latin pinna, wing or fin,
and ped-, foot) or fin-footed mammals are a widely distributed
and diverse group of
semiaquatic marine mammals comprising the families Odobenidae
(the walrus), Otariidae (eared seals, including sea lions
and fur seals), and Phocidae (earless seals).
Pinnipeds are typically sleek-bodied and barrel-shaped. Their
bodies are well adapted to the aquatic habitat where they spend
most of
their lives. Their limbs consist of short, wide, flat flippers.
The smallest pinniped, the Baikal seal, weighs about 70 kg on
average when
full-grown and is 1.3 m long; the largest, the male southern
elephant seal, is over 4 metres long and weighs up to 4,000
kilos.
Pinniped limbs, or flippers, are proportionally shorter than
those of most other mammals. Because the density of water is
much higher than
that of air, pinniped flippers can also be proportionally much
smaller than the wings of birds or bats, relative to total body
size. The digits
of each limb are bound together by a web of skin (fingers and
toes), and have claws on either their front flippers (earless
seals), or their
back flippers (eared seals).
For most pinniped species, molting is an annual process of replacing
worn fur (and in some cases, skin) that temporarily grounds
them. Molting can compromise thermoregulation, so some species,
such as elephant seals, fast and remain onshore for a month
or more.
In many species, pups are born with a natal coat of a different
length, texture and/or color than adults. This coat is adapted
for the
terrestrial, preweaning period, either a thick pelage to keep
them warm in arctic environments, or a thin layer of fur to
keep them cool on
summer sands. During their first molt (about 11 days after birth
for harp seals), the pups replace this with an adult coat better
suited to
life at sea. Until this age, pups risk hypothermia and drowning
if they spend too much time in the ocean.
Pinnipeds can hold their breath for nearly two hours underwater
by conserving oxygen. When the animal starts diving, its heart
rate
slows to about one-tenth of its normal rate. The arteries squeeze
shut and the sense organs and nervous system are the only organs
to
receive normal blood flow. They are able to resist more pain
and fatigue caused by lactic acid accumulation than other mammals.
However, once they return to the surface, they need time to
recover and normalize their body chemistry.
Pinnipeds spend many months at a time at sea and so they must
sleep in the water. Scientists have recorded them sleeping for
minutes
at a time while slowing drifting downward belly up. |
Order: Carnivora
SUBORDER Pinnipedia
Family Otariidae
Subfamily Arctocephalinae
- fur seals
Genus Arctocephalus
Antarctic fur seal,
Arctocephalus gazella
Brown fur seal, Arctocephalus pusillus
South African fur seal,Arctocephalus
pusillus pusillus
Australian fur seal, Arctocephalus pusillus doriferus
Galápagos fur seal, Arctocephalus galapagoensis
Guadalupe fur seal, Arctocephalus townsendi
Juan Fernández fur seal, Arctocephalus philippii
New Zealand fur seal or Southern/Australian fur seal, Arctocephalus
forsteri
South American fur seal,
Arctocephalus australis
Subantarctic fur seal, Arctocephalus
tropicalis
Genus Callorhinus
Northern fur seal,
Callorhinus ursinus
Subfamily Otariinae:
sea lions
Genus Eumetopias
Steller sea
lion, Eumetopias jubatus
Genus Neophoca
Australian sea lion, Neophoca cinerea
Genus Otaria
South American sea lion,
Otaria flavescens
Genus Phocarctos
New Zealand sea lion or Hooker's sea lion, Phocarctos hookeri
Genus Zalophus
California
sea lion, Zalophus californianus
Japanese sea lion, Zalophus japonicus - extinct (1950s)
Galapagos sea lion, Zalophus wollebaeki
Family Phocidae:
true seals
Genus Erignathus
Bearded
seal,
Erignathus barbatus
Genus Cystophora
Hooded seal, Cystophora cristata
Genus Phoca
Tribe Phocini Common seal or harbor seal, Phoca vitulina
Spotted seal, Phoca
largha
Genus Pusa
Ringed seal, Pusa hispida
(formerly Phoca hispida)
Baikal seal, Pusa sibirica (formerly Phoca sibirica)
Caspian seal, Pusa caspica (formerly Phoca caspica)
Genus Pagophilus
Harp seal, Pagophilus groenlandicus (formerly Phoca groenlandica)
Genus Histriophoca
Ribbon seal,
Histriophoca fasciata (formerly Phoca fasciata)
Genus Halichoerus
Grey seal,
Halichoerus grypus
Subfamily Monachinae
Tribe Monachini
Hawaiian Monk
Seal, Monachus schauinslandi, No: Hawaiimunkesel
Mediterranean Monk Seal, Monachus monachus, No: Middelshavsmunkesel
Caribbean Monk Seal, Monachus tropicalis No: Vestindiamunkesel
(probably extinct around 1950 or before 1986)
Tribe Miroungini
Northern Elephant Seal, Mirounga angustirostris, No: Nordlig
sjøelefant
Southern Elephant Seal,
Mirounga leonina, No: Sydlig sjøelefant
Tribe Lobodontini
Ross Seal,
Ommatophoca rossi, No: Rossel
Crabeater Seal,
Lobodon carcinophagus, No: Krabbeetersel
Leopard Seal, Hydrurga
leptonyx, No: Sjøleopard
Weddell Seal, Leptonychotes
weddellii, No: Weddellsel
Family Odobenidae:
walrus
Genus: Odobenus
Atlantic Walrus, Odobenus rosmarus rosmarus - Atlantic Ocean
Pacific
Walrus, Odobenus rosmarus divergens - Pacific
Ocean
Laptev Walrus, Odobenus rosmarus laptevi - Laptev Sea.
|
Fur seals, Arctocephalinae
Brown fur seal (Arctocephalus
pusillus) hauling-out on the Hippolyte Rocks off the east
coast of Tasmania, Australia
Photo:
JJ Harrison |
Fur seals are any of nine species of pinnipeds
in the Otariidae family. One species, the northern fur
seal, Callorhinus ursinus, inhabits
the North Pacific, while seven species in the Arctocephalus
genus are found primarily in the Southern Hemisphere. They are
marked by their dense underfur, which made them a long-time
object of commercial hunting.
Fur seals share with other otariids the ability to turn their
rear limbs forward and move on all fours. Fur seals are generally
smaller than
sea lions. At under 1 metre, the Galapagos fur seal is the smallest
of all pinnipeds. However, their flippers tend to be proportionately
longer, their pelage tends to be darker and the vibrissae more
prominent. Males are often more than five times heavier than
the
females, making them among the most sexually dimorphic of all
mammal groups.
Typically, fur seals gather during the summer months annually
in large assemblages at specific beaches or rocky outcrops to
give birth
and breed. All species are polygynous, meaning dominant males
reproduce with more than one female. For most species, total
gestation lasts about 11.5 months, including a several-month
period of delayed implantation of the embryo. While northern
fur seal
males aggressively select and defend the specific females in
their harems, males of southern species of fur seals tend to
protect spatial
territories, and females are free to choose or switch their
mates according to their own preference or social hierarchy.
After several
continuous days of nursing the newborn pups, females go on extended
foraging trips that can last as long as a week, returning to
the
rookery to feed their pups until they are weaned. Males fast
during the reproductive season, unwilling to leave their females
or
territories.
Thousands
of fur-seals on a St. Paul beach
Photo: NOAA
|
The remainder of the year, fur seals lead a largely pelagic
existence in the open sea pursuing their prey wherever it is
abundant and
plentiful. Fur seals feed on moderately sized fish, squid and
krill. Several species of the southern fur seal also have sea
birds, especially
penguins, as part of their diets. The fur seals themselves are
preyed upon by sharks, orcas and occasionally by larger sea
lions.
Many fur seal species were heavily exploited by commercial sealers,
especially during the 19th century when their fur was highly
valued. ] Many populations, notably the Guadalupe fur seal,
northern fur seal and Cape fur seal, suffered dramatic declines
and are
still recovering. Currently, most species are protected and
hunting is mostly limited to subsistence harvest. Globally,
most populations
can be considered healthy, mostly because they often prefer
remote habitats that are relatively inaccessible to humans.
Nonetheless, environmental degradation, competition with fisheries
and climate change potentially pose threats to some populations.
Source: http://en.wikipedia.org/wiki/Fur_seal |
Sea lions,
Otariinae
Sea
Lion at Monterey Breakwater
Photo: David
Corby |
Sea lions are pinnipeds characterized by external ear flaps,
long foreflippers, the ability to walk on all fours, and short,
thick hair. Together
with the fur seals, they comprise the family Otariidae, or eared
seals. There are six extant and one extinct species (the Japanese
sea lion)
in five genera. Their range extends from the subarctic to tropical
waters of the global ocean in both the Northern and Southern
Hemispheres,
with the notable exception of the northern Atlantic Ocean. They
have an average life span of 20–30 years. A male California
Sea Lion
weighs on an average about 300 kg and is about 2,40m long, while
the female sea lion weighs 100 kg and is 1,50m long.
The largest sea lion is the Steller's sea lion which can weigh
1000 kg and grow to a length of 3m. Sea lions consume large
quantities of
food at a time and are known to eat about 5-8% of their body
weight (about 7 to 18 kilos) at a single feeding.
Source: http://en.wikipedia.org/wiki/Sea_lion |
True
seals, Phocidae
The true seals or earless seals are one of the three main
groups of mammals within the seal superfamily, Pinnipedia. All
true seals are
members of the family Phocidae. They are sometimes called crawling
seals to distinguish them from the fur seals and sea lions of
the family
Otariidae. Seals live in the oceans of both hemispheres
and are mostly confined to polar, subpolar, and temperate climates,
with the
exception of the more tropical monk seals.
Adult phocids vary from 1.15 meters in length and 45 kilograms
in weight, in the ringed seal, to 5 meters and 2,400 kilograms
in the southern elephant seal.
Phocids are more specialized for aquatic life than otariids.
They lack external ears and have sleek, streamlined bodies.
Retractable nipples,
internal testicles and an internal penis sheath provide further
streamlining. A smooth layer of blubber lies underneath the
skin. Phocids are
able to divert blood flow to this layer to help control their
temperatures.
Their fore flippers are used primarily for steering, while their
hind flippers are bound to the pelvis in such a way that they
cannot bring
them under their body to walk on them.
They are more streamlined than fur seals and sea lions, so can
swim more effectively over long distances. However, because
they cannot
turn their hind flippers downward, they are very clumsy on land,
having to wriggle with their front flippers and abdominal muscles.
Phocid respiratory and circulatory systems are adapted to allow
diving to considerable depths, and they can spend a long time
underwater
between breaths. Air is forced from the lungs during a dive
and into the upper respiratory passages, where gases cannot
easily be absorbed
into the bloodstream. This helps protect the seal from the bends.
The middle ear is also lined with blood sinuses that inflate
during diving,
helping to maintain a constant pressure.
Source: http://en.wikipedia.org/wiki/Earless_seal |
Walrus,
Odobenidae
Large walrus on the ice
- Odobenus rosmarus divergens - contemplating the photographer
- Alaska, Bering Sea
Photo: Captain
Budd Christman, NOAA Corps
|
The walrus, Odobenus rosmarus, is a large flippered marine
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 Odobenidae family and Odobenus
genus.
It is subdivided into three subspecies: the Atlantic walrus,
Odobenus rosmarus rosmarus, which lives in the Atlantic
Ocean,
the Pacific walrus, Odobenus rosmarus divergens, which
lives in the Pacific Ocean, and Odobenus rosmarus laptevi,
which lives in the
Laptev Sea.
The walrus is easily recognized by its prominent tusks, whiskers
and great bulk. Adult Pacific males can weigh more than 1,700
kilograms
and, among pinnipeds, are exceeded in size only by the two species
of elephant seals. 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 benthic bivalve 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.
Walrus
Pair
Photo: U.S. Fish and Wildlife Service
|
While some outsized Pacific males can weigh as much as 2,000
kg, most weigh between 800 and 1,680 kg. The Atlantic subspecies
weighs about 10–20% less than the Pacific subspecies. The
Atlantic Walrus also tends to have relatively shorter tusks
and somewhat more
flattened snout. Females weigh about two-thirds as much, with
the Atlantic females averaging 560 kg, sometimes weighing as
little as 400 kg
and the Pacific female averaging 800 kg. Length ranges from
2.2 to 3.6 m. It is the second largest pinniped, after the elephant
seals.
The walrus's 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. Also like
phocids, it lacks external ears.
Walruses live to about 20–30 years old in the wild. The
males reach sexual maturity as early as 7 years, but do not
typically mate until fully
developed around 15 years of age. They rut from January through
April, decreasing their food intake dramatically. The females
begin
ovulating as soon as 4–6 years old. 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.
The females join them and copulate in the water.
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.
Source: http://en.wikipedia.org/wiki/Walrus |
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