Northern fur seal

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Northern fur seal
Northfursealbull.jpg
Northern fur seal bull, St Paul Island, 1992
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Otariidae
Genus: Callorhinus
Gray, 1859
Species:
C. ursinus
Binomial name
Callorhinus ursinus
Callorhinus ursinus distribution.png
Synonyms

Phoca ursinaLinnaeus, 1758

The northern fur seal (Callorhinus ursinus) is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the genus Callorhinus. A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America. [3]

Contents

Description

Male and harem Callorhinus ursinus and harem.jpg
Male and harem

Northern fur seals have extreme sexual dimorphism, with males being 30–40% longer and more than 4.5 times heavier than adult females. [1] 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 in 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 fore flippers and an abrupt "clean line" is seen across the wrist where the fur ends. [4] The hind flippers are proportionately the longest in any otariid because of extremely long, cartilaginous extensions on all of the toes. [4] Small claws are 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 enlarged (thick and wide) necks. A mane of coarse, longer guard hairs extends from the lower neck to the shoulders. [4] and covers the nape, neck, chest, and upper back. While the skulls of adult males are large and robust for their overall size, their heads appear short because of the combination of a short muzzle, and the backs of the head behind the ear pinnae being obscured by the enlarged necks. Adult males have abrupt foreheads formed by the elevation of the crown from development of the sagittal crests, and thicker fur of the mane on the top of their heads.

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.

Fur seal pups, including one rare albino Pups 01.jpg
Fur seal pups, including one rare albino

Adult females, subadults, and juveniles are moderate in build. Distinguishing the sexes is difficult until about age five. 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. Variable cream to rust-colored areas are 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. Their manes 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 three to four 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 weigh 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 3.1.4.22.1.4.1 [5]

Close up of face and ears Fur seal face.jpg
Close up of face and ears

Like other otariids, northern fur seals are built for efficient terrestrial locomotion. Their hind limbs are in a plantigrade stance and are able to rotate under the body for quadrupedal locomotion and support. [6] When swimming, there are two different types of movement: locomotion and diving. These seals swim primarily with forelimb propulsion due to their physiology. They have flexible joints between vertebrae for better maneuverability in the water as well as “greater muscular leverage” for pectoral strokes. [7] Stroke patterns are different for different dive types and locomotion, and stroke rates vary for individuals since there's a relationship between maximum stroke rate and body size. [8]

Distribution and habitat

Overview of rookery Northern fur seal rookery tuleny.jpg
Overview of rookery

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 to the southern tip of the Baja California Peninsula, the Sea of Okhotsk, and the Bering Sea. [9] An estimated 1.1 million northern fur seals occur across the range, of which roughly half breed on the Pribilof Islands in the east Bering Sea. Another 200–250 thousand breed on the Commander Islands in the west Bering Sea, some 100,000 breed on Tyuleniy Island off the coast of Sakhalin in the southwest Sea of Okhotsk, and another 60–70 thousand in the central Kuril Islands in Russia. Smaller rookeries (around 5,000 animals) are found on Bogoslof Island in the Aleutian Chain, San Miguel Island in the Channel Island group and South Farallon Island off the coast of California. [10] [11] Recent evidence from stable isotope analysis of Holocene fur seal bone collagen (δ13C and δ15N) indicates that before the maritime fur trade, 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. [12]

During the winter, northern fur seals display a net movement southward, with animals from Russian rookeries regularly entering Japanese and Korean waters in the Sea of Japan and Alaskan animals moving along the central and eastern Pacific to British Columbia, Canada and as far south as Baja California.

The northern fur seal's range overlaps almost exactly with that of Steller sea lions; occasional cohabitation occurs at reproductive rookeries, notably in the Kurils, the Commander Islands, and Tyulen'i Islands. The only other fur seal found in the Northern Hemisphere is the Guadalupe fur seal which overlaps slightly with the northern fur seal's range in California.

Ecology

Fur seals are opportunistic feeders, primarily feeding on pelagic fish and squid depending on local availability. Identified fish prey include hake, herring, lantern fish, capelin, pollock, and mackerel. [9] Their feeding behavior is primarily solitary.

Northern fur seals are preyed upon primarily by sharks and killer whales. [9] Occasionally, very young animals are eaten by Steller sea lions. [9] Occasional predation on live pups by Arctic foxes 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 foxes.

Reproductive behavior

Seals enter breeding rookeries in May. Generally, older males (10 years and older) return first and compete for prime breeding spots on the rookeries. They remain on the rookery, fasting throughout the duration of the breeding season. [9] 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 which 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. [13] Deaths of females as a consequence of these conflicts have been recorded, though the males themselves are rarely seriously injured. [13] Young males unable to acquire and maintain a territory of a harem typically aggregate in neighboring "haulouts", occasionally making incursions into the reproductive sections of the rookery in an attempt to displace an older male.

Northern fur seal pups CuRRnfursealpups.jpg
Northern fur seal pups

After remaining with their pups for the first eight to ten days of their lives, 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 seal females, though young males might disperse to other existing rookeries, or occasionally find new haulouts. [13]

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 implantation occurs four months after fertilization. In total, gestation lasts around a year, such that the pups born in a given summer are the product of the previous year's breeding cycle.

Status

An orca feeding on a Northern fur seal Orca feeding at Bogoslof Island.jpg
An orca feeding on a Northern fur seal

Recently, concern about the status of fur seal populations has increased, particularly in the Pribilof Islands, where pup production has decreased about 50% since the 1970s, with a continuing drop of about 6–7% per year. This has caused them to be listed as "vulnerable" under the U.S. Endangered Species Act, and has led to an intensified research program into their behavioral and foraging ecology. Possible causes are increased predation by killer whales, competition with fisheries, and climate change effects, but to date, no scientific consensus has been reached. The IUCN (2008) lists the species as globally threatened under the category "vulnerable".

Fur trade

Men killing fur seals on Saint Paul Island, Alaska, 1890s Killing fur seals, St Paul Island.jpg
Men killing fur seals on Saint Paul Island, Alaska, 1890s

Northern fur seals have been a staple food of native northeast Asian and Alaska Native peoples for thousands of years. The arrival of Europeans to Kamchatka and Alaska 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, a key rookery 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 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 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. [14] 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. [15] Currently, a subsistence hunt by the residents of St. Paul Island and an insignificant harvest in Russia are allowed.

See also

Related Research Articles

Earless seal family of mammals

The earless seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, 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, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Fur seal subfamily of mammals

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, belongs to a different genus and inhabits the North Pacific.

Eared seal family of mammals

An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

California sea lion the fastest living species pinniped in the world

The California sea lion is a coastal eared seal native to western North America. It is one of six species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and great white sharks.

Sea lion Subfamily of aquatic mammals

Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short, thick hair, and a big chest and belly. Together with the fur seals, they comprise the family Otariidae, eared seals, which contains six extant and one extinct species 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 lifespan of 20–30 years. A male California sea lion weighs on average about 300 kg (660 lb) and is about 2.4 m (8 ft) long, while the female sea lion weighs 100 kg (220 lb) and is 1.8 m (6 ft) long. The largest sea lion is Steller's sea lion, which can weigh 1,000 kg (2,200 lb) and grow to a length of 3.0 m (10 ft). Sea lions consume large quantities of food at a time and are known to eat about 5–8% of their body weight at a single feeding. Sea lions can move around 16 knots in water and at their fastest they can reach a speed of about 30 knots. Three species, the Australian sea lion, the Galápagos sea lion and the New Zealand sea lion are listed as Endangered.

Pinniped Infraorder of mammals

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae. There are 33 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the order Carnivora and their closest living relatives are believed to be bears and the superfamily of musteloids, having diverged about 50 million years ago.

Steller sea lion The largest living sea lion and eared seal in the world

The Steller sea lion, also known as the Steller's sea lion and "northern sea lion", is a near-threatened species of sea lion in the northern Pacific. It is the sole member of the genus Eumetopias and the largest of the eared seals (Otariidae). Among pinnipeds, it is inferior in size only to the walrus and the two species of elephant seals. The species is named for the naturalist Georg Wilhelm Steller, who first described them in 1741. The Steller sea lion has attracted considerable attention in recent decades, owing to significant and largely unexplained declines in their numbers over an extensive portion of their northern range in Alaska.

St. Paul, Alaska City in Alaska, United States

St. Paul is a city in the Aleutians West Census Area, Alaska, United States. It is the main settlement of Saint Paul Island in the Pribilofs, a small island group in the Bering Sea. Saint Paul Island is well known as a birdwatching haven. The population was 479 at the 2010 census, down from 532 in 2000.

Northern elephant seal The second largest living pinniped in the world

The northern elephant seal is one of two species of elephant seal. It is a member of the family Phocidae. Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.

Elephant seal genus of mammals

Elephant seals are large, oceangoing earless seals in the genus Mirounga. The two species, the northern elephant seal and the southern elephant seal, were both hunted to the brink of extinction by the end of the 19th century, but their numbers have since recovered.

Antarctic fur seal species of mammal

The Antarctic fur seal, is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. Despite what its name suggests, the Antarctic fur seal is mostly distributed in Subantarctic islands and its scientific name is thought to have come from the German vessel SMS Gazelle, which was the first to collect specimens of this species from Kerguelen Islands.

Juan Fernández fur seal species of mammal

The Juan Fernández fur seal is the second smallest of the fur seals, second only to the Galápagos fur seal. They are found only on the Pacific Coast of South America, more specifically on the Juan Fernández Islands and the Desventuradas Islands. There is still much that is unknown about this species. Scientists still do not know the average life span of this species, or the diet and behavior of males apart from the breeding season.

Galápagos fur seal species of mammal

The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.

Brown fur seal species of fur seal

The brown fur seal, also known as the Cape fur seal, South African fur seal, and Australian fur seal, is a species of fur seal.

South American sea lion species of mammal

The South American sea lion, also called the Southern Sea Lion and the Patagonian sea lion, is a sea lion found on the Ecuadorian, Peruvian, Chilean, Falkland Islands, Argentinean, Uruguayan, and Southern Brazilian coasts. It is the only member of the genus Otaria. Its scientific name was subject to controversy, with some taxonomists referring to it as Otaria flavescens and others referring to it as Otaria byronia. The former eventually won out, although that may still be overturned. Locally, it is known by several names, most commonly lobo marino (es)/lobo marinho (pt) and león marino (es)/leão marinho (pt) and the hair seal.

Australian sea lion species of mammal

The Australian sea lion, also known as the Australian sea-lion or Australian sealion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently monotypic in the genus Neophoca, with the extinct Pleistocene New Zealand sea lion Neophoca palatina the only known congener. These sea lions are sparsely distributed through Houtman Arbrolhos Islands in Western Australia and The Pages Islands in southern Australia. With a population estimated at around 14,730 animals, the Wildlife Conservation Act of Western Australia (1950) has listed them as “in need of special protection”. Their Conservation status is listed as endangered. These pinnipeds are specifically known for their abnormal breeding cycles, which are varied between a 5-month breeding cycle and a 17- to 18-month aseasonal breeding cycle, compared to other pinnipeds which fit into a 12-month reproductive cycle. Females are either silver or fawn with a cream underbelly and males are dark chocolate brown with a yellow mane and are bigger than the females.

New Zealand sea lion species of mammal

The New Zealand sea lion, also known as Hooker's sea lion, and whakahao in Māori, is a species of sea lion that primarily breeds on New Zealand's subantarctic Auckland and Campbell islands and to some extent around the coast of New Zealand's South and Stewart islands. The New Zealand sea lion numbers around 10,000 and is perhaps the world's rarest sea lion species. They are the only species of the genus Phocarctos.

Caspian seal species of mammal

The Caspian seal is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. They are found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea. In winter, and cooler parts of the spring and autumn season, these marine mammals populate the Northern Caspian. As the ice melts in the warmer season, they can be found on the mouths of the Volga and Ural Rivers, as well as the southern latitudes of the Caspian where cooler waters can be found due to greater depth.

Ribbon seal Species of mammal

The ribbon seal is a medium-sized pinniped from the true seal family (Phocidae). A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white strips and two white circles against dark brown or black fur.

Harbor seal Species of mammal

The harborseal, also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere. The most widely distributed species of pinniped, they are found in coastal waters of the northern Atlantic, Pacific Oceans, Baltic and North Seas.

References

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Further reading