Fur seals are any of nine species of
pinnipeds belonging to the subfamily
Arctocephalinae in the family
Otariidae. They are much more closely related to
sea lions than
true seals, and share with them external ears (
pinnae), relatively long and muscular foreflippers, and the ability to walk on all fours. They are marked by their dense
underfur, which made them a long-time object of commercial
hunting. Eight species belong to the genus
Arctocephalus and are found primarily in the Southern Hemisphere, while a ninth species also sometimes called fur seal, the
northern fur seal (
Callorhinus ursinus), belongs to a different genus and inhabits the North Pacific.
Taxonomy
- Subfamily Arctocephalinae
- Genus Arctocephalus
- Antarctic fur seal, A. gazella
- Brown fur seal, A. pusillus
- South African fur seal, A. pusillus pusillus
- Australian fur seal, A. pusillus doriferus
- Galápagos fur seal, A. galapagoensis
- Guadalupe fur seal, A. townsendi
- Juan Fernández fur seal, A. philippii
- New Zealand fur seal or southern fur seal, A. forsteri
- South American fur seal, A. australis
- Subantarctic fur seal, A. tropicalis
- Genus Callorhinus
Fur seals and sea lions make up the family Otariidae. Along with
Phocidae and Odobodenidae, ottariids are pinnipeds descending from a
common ancestor most closely related to modern bears. The name pinniped
refers to mammals with front and rear flippers. Otariids arose about
15-17 million years ago in the Miocene, and were originally land mammals
that rapidly diversified and adapted to a marine environment, giving
rise to the semi-aquatic marine mammals that thrive today. Fur seals and
sea lions are closely related and commonly known together as the "eared
seals".
Until recently, fur seals were all grouped under a single subfamily of
Pinnipedia, called Arctocephalinae, to contrast them with Otariinae –
the sea lions – based on the most prominent common feature, namely the
coat of dense underfur intermixed with guard hairs. Recent genetic
evidence, however, suggests
Callorhinus is more closely related
to some sea lion species, and the fur seal/sea lion subfamily
distinction has been eliminated from many
taxonomies.
Nonetheless, all fur seals have certain features in common: the fur,
generally smaller sizes, farther and longer foraging trips, smaller and
more abundant prey items and greater
sexual dimorphism. For these reasons, the distinction remains useful. Fur seals comprise two genera:
Callorhinus, and
Arctocephalus.
Callorhinus is represented by just one species in the northern hemisphere, the northern fur seal (
Callorhinus ursinus), and
Arctocephalus is represented by eight species in the southern hemisphere. The southern fur seals comprising the genus
Arctocephalus
include: Antarctic fur seals, Galapagos fur seals, Juan Fernandez fur
seals, New Zealand fur seals, brown fur seals, South American fur seals,
and Subantarctic fur seals.
Physical appearance
Along with the previously mentioned thick underfur, fur seals are
distinguished from sea lions by their smaller body structure, greater
sexual dimorphism, smaller prey, and longer foraging trips during the
feeding cycle. The physical appearance of fur seals varies with
individual species but the main characteristics remain constant. Fur
seals are characterized by their external pinnae, dense underfur,
vibrissae, and long muscular limbs. They share with other otariids the
ability to rotate their rear limbs forward, supporting their body and
allowing them to ambulate on land. In water their front limbs,
typically measuring about 1/4th their body length, act as oars and can
propel them forward for optimal mobility. The surfaces of these long,
paddle-like fore limbs are leathery with small claws. Otariids have a
dog-like head, sharp, well-developed canines, sharp eyesight and keen
hearing. They are extremely sexually dimorphic mammals, with the males
often 2 to 5 times the size of the females, with proportionally larger
heads, necks and chests. Size ranges from about 1.5 m, 64 kg in the
male Galapagos fur seal (also the smallest pinniped) to 2.5m, 180 kg in
the adult male New Zealand fur seal. Most fur seal pups are born with a
black-brown coat that molts at 2–3 months, revealing a brown coat that
typically gets darker with age. Some males and females within the same
species have significant differences in appearance, further contributing
to the sexual dimorphism. Females and juveniles often have a lighter
colored coat overall or only on the chest, as seen in South American fur
seals. In a Northern fur seal population, the females are typically
silvery-gray on the dorsal side and reddish-brown on their ventral side
with a light gray patch on their chest. This makes them easily
distinguished from the males with their brownish-gray to reddish-brown
or black coats.
Habitat
Of the
fur seal family, eight species are considered southern fur seals, and
only one is found in the northern hemisphere. The southern group
includes Antarctic, Galapagos, Guadalupe, Juan Fernandez, New Zealand,
Brown, South American, and Subantarctic fur seals. They typically spend
about 70% of their lives in subpolar, temperate, and equatorial waters.
Colonies of fur seals can be seen throughout the Pacific and Southern
oceans from south Australia, Africa, and New Zealand, to the coast of
Peru and up to California. They are typically non migrating mammals,
with the exception of the Northern fur seal which has been known to
travel distances up to 10,000 km. Fur seals are often found near
isolated islands or peninsulas and can be seen hauling out onto the
mainland during winter. Although they are not migratory, they have been
observed wandering hundreds of miles from their breeding grounds in
times of scarce resources. For example, the Subantarctic fur seal
typically resides near temperate islands in the South Atlantic and
Indian Oceans north of the Antarctic Polar Front, but juvenile males
have been seen wandering as far north as Brazil and South Africa.
Behavior and ecology
A fur seal rookery with thousands of seals
Typically, fur seals gather during the summer 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. Northern fur seal males aggressively select and defend the specific females in their harms.
[1]
Females typically reach sexual maturity around 3–4 years. The males
reach sexual maturity around the same time but do not become territorial
or mate until 6–10 years. The breeding season typically begins in
November and lasts 2–3 months. The Northern fur seals begin their
breeding season as early as June due to their region, climate, and
resources. In all cases, the males arrive a couple of weeks early to
fight for their territory and groups of females to mate with. They
congregate at rocky, isolated breeding grounds and defend their
territory through fighting and vocalization. Males typically do not
leave their territory for the entirety of the breeding season, fasting
and competing until all energy sources are depleted. The Juan Fernandez
fur seals deviate from this typical behavior, using aquatic breeding
territories not seen in other fur seals. They use rocky sites for
breeding but males fight for territory on land and on the shoreline
& in the water. Upon arriving to the breeding grounds, females give
birth to their pups from the previous season. About a week later, the
females will mate again and shortly after begin their feeding cycle.
The feeding cycle typically consists of foraging and feeding at sea for
about 5 days, then returning to the breeding grounds to nurse the pups
for about 2 days. Mothers and pups locate each other using call
recognition during nursing period. The Juan Fernandez fur seal has a
particularly long feeding cycle, with about 12 days of foraging and
feeding and 5 days of nursing. Most fur seals continue this cycle for
about 9 months until they wean their pup. The exception to this is the
Antarctic fur seal, which has a feeding cycle that lasts only 4 months.
During foraging trips, most female fur seals travel around 200 km from
the breeding site, and can dive around 200m depending on food
availability.
The remainder of the year, fur seals lead a largely
pelagic existence in the open sea, pursuing their prey wherever it is abundant. 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.
[2][3] The fur seals, in turn, are preyed upon by
sharks,
killer whales,
and occasionally by larger sea lions. Fur seals are opportunistic
mammals tend to feed and dive in shallow waters at night, when their
prey are swimming near the surface. The South American fur seals
exhibit a different diet; adults feed almost exclusively on anchovies
while juveniles feed on demersal fish, most likely due to availability.
When fur seals were hunted in the late 18th and early 19th
centuries, they hauled out on remote islands where no predators were
present. The hunters reported being able to club the unwary animals to
death one after another, making the hunt profitable, though the price
per seal skin was low.
[4]
Population and survival
The average lifespan of fur seals varies with different species from
13 to 25 years with females typically living longer. Most populations
continue to expand as they recover from previous commercial hunting and
environmental threats.
Many fur seal species were heavily exploited by commercial
sealers, especially during the 19th century when their fur was highly valued. Beginning in the 1790s, the ports of
Stonington and
New Haven,
Connecticut, were leaders of the American fur seal trade, which
primarily entailed clubbing fur seals to death on uninhabited South
Pacific islands, skinning them, and selling the hides in
China.
[4] 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.
See also
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