Northern Fur Seal
Overview
The Northern fur seal is an eared seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

 found along the north Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, the Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....

 and the Sea of Okhotsk
Sea of Okhotsk
The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...

. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only species in the genus Callorhinus.
Northern fur seals have extreme sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

, with males being 30–40% longer and more than 4.5 times heavier than adult females. The head is foreshortened in both sexes because of the very short down-curved muzzle, and small nose, which extends slightly beyond the mouth in females and moderately in males.
Encyclopedia
The Northern fur seal is an eared seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

 found along the north Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, the Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....

 and the Sea of Okhotsk
Sea of Okhotsk
The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...

. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only species in the genus Callorhinus.

Physical description

Northern fur seals have extreme sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

, with males being 30–40% longer and more than 4.5 times heavier than adult females. The head is foreshortened in both sexes because of the very short down-curved muzzle, and small nose, which extends slightly beyond the mouth in females and moderately in males. The pelage is thick and luxuriant, with a dense underfur that is a creamy color. The underfur is obscured by the longer guard hairs, although it is partially-visible when the animals are wet. Features of both fore and hind flippers are unique and diagnostic of the species. Fur is absent on the top of the fored flippers and there is an abrupt "clean line" across the wrist where the fur ends. The hind flippers are proportionately the longest in any otariid because of extremely long, cartilaginous extensions on all of the toes. There are small claws on digits 2–4, well back from the flap-like end of each digit. The ear pinnae are long and conspicuous, and naked of dark fur at the tips in older animals. The mystacial vibrissae can be very long, and regularly extend beyond the ears. Adults have all white vibrissae, juveniles and subadults have a mixture of white and black vibrissae, including some that have dark bases and white ends, and pups and yearlings have all-black vibrissae. The eyes are proportionately large and conspicuous, especially on females, subadults, and juveniles.

Adult males are stocky in build, and have an enlarged neck that is thick and wide. A mane of coarse longer guard hairs extends from the lower neck to the shoulders. and covers the nape, neck, chest, and upper back. While the skull of adult males is large and robust for their overall size, the head appears short because of the combination of a short muzzle, and the back of the head behind the ear pinnae being obscured by the enlarged neck. Adult males have an abrupt forehead formed by the elevation of the crown from development of the sagittal crest, and thicker fur of the mane on the top of the head.

Canine teeth are much longer and have a greater diameter in adult males than those found on adult females, and this relationship holds to a lesser extent at all ages.

Adult females, subadults and juveniles, are moderate in build. It is difficult to distinguish the sexes until about age 5. The body is modest in size and the neck, chest, and shoulders are sized in proportion with the torso. Adult females and subadults have more complex and variable coloration than adult males. They are dark-silver-gray to charcoal above. The flanks, chest, sides, and underside of the neck, often forming a chevron pattern in this area, are cream to tan with rusty tones. There are variable cream to rust-colored areas on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. In contrast, adult males are medium gray to black, or reddish to dark brown all over. The mane can have variable amounts of silver-gray or yellowish tinting on the guard hairs. Pups are blackish at birth, with variable oval areas of buff on the sides, in the axillary area, and on the chin and sides of the muzzle. After 3–4 months, pups molt to the color of adult females and subadults.

Males can be as large as 2.1 m and 270 kg. Females can be up to 1.5 m and 50 kg or more. Newborns weigh 5.4–6 kg, and are 60–65 cm long.

The teeth are haplodont, i.e. sharp, conical and mostly single-rooted, as is common with carnivorous marine mammals adapted to tearing fish flesh. As with most Caniforms, the upper canines are prominent. The dental formula of the adult is

Range

The northern fur seal is found in the north Pacific – its southernmost reach is a line that runs roughly from the southern tip of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 to the southern tip of the Baja California peninsula
Baja California Peninsula
The Baja California peninsula , is a peninsula in northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The Peninsula extends from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south.The total area of the Baja California...

, the Sea of Okhotsk
Sea of Okhotsk
The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...

 and the Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....

. There are estimated to be around 1.1 million Northern Fur Seals across the range, of which roughly one half breeds on the Pribilof Islands
Pribilof Islands
The Pribilof Islands are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of Unalaska and 200 miles southwest of Cape Newenham. The Siberia coast is roughly northwest...

 in the east Bering Sea. Another 200–250,000 breed on the Commander Islands in the west Bering Sea and some 100,000 breed on Tyuleni Island off the coast of Sakhalin
Sakhalin
Sakhalin or Saghalien, is a large island in the North Pacific, lying between 45°50' and 54°24' N.It is part of Russia, and is Russia's largest island, and is administered as part of Sakhalin Oblast...

 in the southwest Sea of Okhotsk and another 60–70,000 in the central Kuril Islands
Kuril Islands
The Kuril Islands , in Russia's Sakhalin Oblast region, form a volcanic archipelago that stretches approximately northeast from Hokkaidō, Japan, to Kamchatka, Russia, separating the Sea of Okhotsk from the North Pacific Ocean. There are 56 islands and many more minor rocks. It consists of Greater...

 in Russia. Smaller rookeries (around 5,000 animals) are found on Bogoslof Island in the Aleutian Chain and San Miguel Island
San Miguel Island
San Miguel Island is the westernmost of California's Channel Islands, located across the Santa Barbara Channel in the Pacific Ocean, within Santa Barbara County, California. San Miguel is the sixth-largest of the eight Channel Islands at , including offshore islands and rocks. Prince Island, off...

 in the Channel Island
Channel Islands of California
The Channel Islands of California are a chain of eight islands located in the Pacific Ocean off the coast of Southern California along the Santa Barbara Channel in the United States of America...

 group off the coast of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. Recent evidence from stable isotope analysis of Holocene fur seal bone collagen (δ13C and δ15N) indicate that prior to the maritime fur trade
Maritime Fur Trade
The Maritime Fur Trade was a ship-based fur trade system that focused on acquiring furs of sea otters and other animals from the indigenous peoples of the Pacific Northwest Coast and natives of Alaska. The furs were mostly sold in China in exchange for tea, silks, porcelain, and other Chinese...

, it was more common for these animals to breed at local rookeries in British Columbia, California and likely along much of the northwest coast of North America.

During the winter months, northern fur seals display a net movement southward, with animals from Russian rookeries regularly entering Japanese and Korean waters in the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...

 and Alaskan animals moving along the central and eastern Pacific as far as Baja California.

The northern fur seal's range overlaps almost exactly with that of Steller sea lions, with which they occasionally cohabit reproductive rookeries, notably in the Kurils, the Commander Islands and Tyuleni Island. The only other fur seal found in the northern hemisphere is the Guadalupe Fur Seal
Guadalupe Fur Seal
The Guadalupe fur seal is one of six members of the fur seal genus Arctocephalus. Sealers reduced the population to just a few dozen by the late 19th century, but the species had recovered to 10,000 in number by the late 1990s...

 which overlaps slightly with the northern fur seal's range in California.

Ecology

Fur seals are opportunistic feeders, primarily feeding on pelagic fish
Pelagic fish
Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...

 and squid depending on local availability. Identified fish prey include hake
Hake
The term hake refers to fish in either of:* family Phycidae of the northern oceans* family Merlucciidae of the southern oceans-Hake fish:...

, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, lantern fish, capelin
Capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...

, pollock
Pollock
Pollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...

 and mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

. Their feeding behavior is primarily solitary.

Northern fur seals are preyed upon primarily by shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s and orca
Orca
The killer whale , commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas...

s. Occasionally, very young animals will be eaten by Steller sea lions. Occasional predation on live pups by arctic fox
Arctic fox
The arctic fox , also known as the white fox, polar fox or snow fox, is a small fox native to Arctic regions of the Northern Hemisphere and is common throughout the Arctic tundra biome. The Greek word alopex, means a fox and Vulpes is the Latin version...

es has also been observed.

Due to very high densities of pups on reproductive rookeries and the early age at which mothers begin their foraging trips, mortality can be relatively high. Consequently, pup carcasses are important in enriching the diet of many scavengers, in particular gulls and arctic fox
Arctic fox
The arctic fox , also known as the white fox, polar fox or snow fox, is a small fox native to Arctic regions of the Northern Hemisphere and is common throughout the Arctic tundra biome. The Greek word alopex, means a fox and Vulpes is the Latin version...

es.

Reproductive behavior

Seals aggregate on traditional breeding grounds (rookeries) in May. Generally older males (10 years and older) return first and compete for prime breeding spots on the rookeries. They will remain on the rookery fasting throughout the duration of the breeding season. The females come somewhat later and give birth shortly thereafter. Like all other otariids, northern fur seals are polygynous, with some males breeding with up to 50 females in a single breeding season. Unlike Steller sea lions, with whom they share habitat and some breeding sites, Northern fur seals are possessive of individual females in their harem, often aggressively competing with neighboring males for females. Deaths of females as a consequence of 'tug-of-war's have been recorded, though the males themselves are rarely seriously injured. Young males unable to acquire and maintain a territory of a harem typically aggregate in neighboring "haulouts
Hauling-out
Hauling-out is the behaviour associated with pinnipeds , of temporarily leaving the water between periods of foraging activity for sites on land or ice...

" occasionally making incursions into the reproductive sections of the rookery in an attempt to displace an older male.

After remaining with their pups for the first eight to ten days of their life, females begin foraging trips lasting up to a week. These trips last for about four months before weaning, which happens abruptly, typically in October. Most of the animals on a rookery enter the water and disperse towards the end of November, typically migrating southward. Breeding site fidelity is generally high for fur seals females, though young males might disperse to other existing rookeries, or occasionally found new haulouts.

Peak mating occurs somewhat later than peak birthing from late June to late July. As with many other otariids, the fertilized egg undergoes delayed implantation: after the blastocyst stage occurs, development halts and implantantion occurs four months after fertilization. In total, gestation lasts for approximately one year, such that the pups born in a given summer are the product of the previous year's breeding cycle.

Status

Recently there has been increased concern about the status of fur seal populations, particularly in the Pribilof Islands
Pribilof Islands
The Pribilof Islands are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of Unalaska and 200 miles southwest of Cape Newenham. The Siberia coast is roughly northwest...

, where there has been a roughly 50% decrease in pup-production since the 1970s and a continuing drop in pup production of about 6–7% per year. This has caused them to be listed as "vulnerable" under the U.S. Endangered Species Act
Endangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...

 and has led to an intensified research program into their behavioral and foraging ecology. Possible causes are increased predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

 by orcas, competition with fisheries and climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 effects, but there is, to date, no scientific consensus. The IUCN (2008) lists the species as globally threatened under the category "vulnerable".

Fur trade

Northern fur seals have been a staple food of native northeast Asian and Alaskan Inuit peoples for thousands of years. The arrival of Europeans to Kamchatka and Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 in the 17th and 18th centuries, first from Russia and later from North America, was followed by a highly extractive commercial fur trade. The commercial fur trade was accelerated in 1786, when Gavriil Pribylov discovered St. George Island
St. George Island (Alaska)
St. George Island is one of the Pribilof Islands of the state of Alaska, USA, in the Bering Sea off the western coast of the state. The island has a land area of 90 km² and a population of about 100 people, all living in its only community, the city of St...

, a key rookery
Rookery
A rookery is a colony of breeding animals, generally birds. A rook is a Northern European and Central Asian member of the crow family, which nest in prominent colonies at the tops of trees. The term is applied to the nesting place of birds, such as crows and rooks, the source of the term...

 of the seals. An estimated 2.5 million seals were killed from 1786 to 1867. This trade led to a decline in fur seal numbers. Restrictions were first placed on fur seal harvest on the Pribilof Islands
Pribilof Islands
The Pribilof Islands are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of Unalaska and 200 miles southwest of Cape Newenham. The Siberia coast is roughly northwest...

 by the Russians in 1834. Shortly after the United States purchased Alaska from Russia in 1867, the U.S. Treasury was authorized to lease sealing privileges on the Pribilofs, which were granted somewhat liberally to the Alaska Commercial Company. From 1870 to 1909, pelagic sealing proceeded to take a significant toll on the fur seal population, such that the Pribilof population, historically numbering on the order of millions of individuals, reached a low of 216,000 animals in 1912.

Significant harvest was more or less arrested with the signing of the North Pacific Fur Seal Convention of 1911
North Pacific Fur Seal Convention of 1911
The North Pacific Fur Seal Convention of 1911, formally known as the Convention between the United States and Other Powers Providing for the Preservation and Protection of Fur Seals, was an international treaty signed on July 7, 1911 designed to manage the commercial harvest of fur bearing mammals ...

 by Great Britain (on behalf of Canada), Japan, Russia and the United States. The Convention of 1911 remained in force until the onset of hostilities among the signatories during World War II, and is also notable as the first international treaty to address the conservation of wildlife. A successive convention was signed in 1957 and amended by a protocol in 1963. "The international convention was put into effect domestically by The Fur Seal Act of 1966 (Public Law 89-702)," said an Interior Department review of the history. Currently, there is a subsistence hunt by the residents of St. Paul Island and an insignificant harvest in Russia.

Further reading

  • Heptner, V. G.; Nasimovich, A. A; Bannikov, Andrei Grigorevich; Hoffmann, Robert S, Mammals of the Soviet Union, Volume II, part 3 (1996). Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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