SPOTTED SEAL

 

In Echizen Matsushima Aquarium, Japan

The spotted seal (Phoca largha), also known as the larga seal or largha seal, is a member of the family Phocidae, and is considered a "true seal". It inhabits ice floes and waters of the North Pacific Ocean and adjacent seas. It is primarily found along the continental shelf of the Beaufort, Chukchi, Bering and Okhotsk Seas and south to the northern Yellow Sea and it migrates south as far as northern Huanghai and the western Sea of Japan. It is also found in Alaska from the southeastern Bristol Bay to Demarcation Point during the ice-free seasons of summer and autumn when spotted seals mate and have pups. Smaller numbers are found in the Beaufort Sea. It is sometimes mistaken for the harbor seal to which it is closely related and spotted seals and harbor seals often mingle together in areas where their habitats overlap.

The reduction in arctic ice floes due to global warming led to concerns that the spotted seal was threatened with extinction. Studies were conducted on its population numbers, with the conclusion, as of October 15, 2009, that the spotted seal population in Alaskan waters is not currently to be listed as endangered by NOAA.

Distinctive characteristics

The spotted seal is a sibling species with the harbor seal. Their coloration is generally pale, silver gray above and below, with a darker mantle dominated by even darker oval spots of fairly uniform size (1-2 cm) and generally oriented parallel to the long axis of the body. There may be light rings around some spots, or large irregular spots or blotches. Spotting tends to be of fairly even distribution and darkness overall. In harbor seals, spots are more faded and sparse on the underside. The face and muzzle are darker. Pups are born with a long and woolly whitish lanugo, which is shed 2-4 weeks after birth. All of the Alaskan seals have 34 teeth composed of six upper incisors, four lower incisors, two upper canines, two lower canines, eight upper post canines, eight lower post canines, two upper molars, and two lower molars.

Dental formula    I 3/2, C1/1, PC 5/5.

Size

Adult males are up to 1.7 m and females to 1.6 m long. Adults weigh 82-123 kg. At birth, spotted seals are 77-92 cm long and weigh 7-12 kg.

Life Span

Average of Males live up to 30 years; Female live up to 32 years. About 45% of spotted seal pups die with in their first year of life. Range life both lives up to 35 years.

Gestation Period    315 days.

Can be confused with

In addition to harbor seals, spotted seals share their range with ringed and ribbon seals. Ribbon seals lack spots and have broad bands on a black or brown body, or as juveniles are dull gray above and lighter below, but in all age classes and both sexes ribbon seals lack the abundant spots of the spotted seal.

The range of the eastern Pacific and Western Pacific subspecies of the harbor seal overlaps with the range of the spotted seal. Unfortunately, the consistent differences between the species are features of the skull and genetic characteristics. Coloration, body size and shape, and size of features overlap in the two species. Some of the best features are behavioral. Spotted seals give birth on sea ice and usually are alone or accompanied by a male. Harbor seals give birth in haul-out groups typical of the sites where they are found year-round. In addition to being born in a long gray lanugo coat, spotted seals spend their first weeks on the ice, while harbor seals are generally born in a short hair coat similar to the adult, and are able to swim within hours of birth. Where they co-occur, spotted seals give birth up to 2 months earlier than harbor seals.

Spotted seals and ringed seals can be easily confused. Spotted seals are longer and proportionately leaner, with a longer neck, head, and muzzle. Spotted seals rarely have many rings, whereas ringed seals have an abundance of rings and a low density of less conspicuous spots. Pups of both species are born in a long, grayish lanugo coat and would be difficult to tell apart if away from adults. However, spotted seal pups are born on top of ice floes, whereas ringed seal pups are born in lairs under snow and ice.

Spotted seals haul-out on land, and can be found mixed in with groups of harbor seals in at least Bristol Bay, Alaska, and are said to be separable from harbor seals only by experienced observers based on behavior, response to disturbance, and subtle differences in facial features.

Distribution

Spotted seals are widespread in the Sea of Okhotsk and the Sea of Japan, and reach China in the northern Yellow Sea. They are widespread in the Bering and Chukchi Seas and range north into the Arctic Ocean north to about the edge of the continental shelf, west to about 170°E and east to the Mackenzie River Delta in Canada. They inhabit the southern edges of the pack ice from winter to early summer. In late summer and fall, ringed seals move into coastal areas, including river mouths. They breed exclusively, and haul-out regularly, on sea ice, but do come ashore on beaches and sandbars.

Ecology and behavior

Female spotted seals become sexually mature at 3–4 years of age and males about a year later. Male and female pairs form prior to pupping and they appear to be monogamous throughout the mating season; a unique breeding system among ice seal species. The females give birth annually to a single pup in April or May when the ice is the most stable. The pup, mother, and her mate remain in close proximity until the pup is weaned around 4 to 6 weeks. The female is ready to mate after the pup is weaned. Copulation has been reported to occur under water, another uncommon behavior when compared to other ice seals. New-born pups are about 35 inches (89 cm) long and weigh about 20 pounds (9 kg). Pups are born with a soft white coat called lanugo. The white color may provide camouflage to hide from predators; however the most important advantage of lanugo is its insulated properties in air. Lanugo keeps pups warm until they develop a blubber layer for warmth. The lanugo is shed at the time of weaning when pups are about four weeks old. During the suckling period, pups triple their body weight by adding to their blubber layer. After weaning, the pup uses the energy and nutrients stored in the blubber while it learns to dive and forage. When the lanugo is shed the new coat is similar to that of an adult spotted seal. The gestation period for spotted seals is about 10.5 months with a delayed implantation of the embryo of about 2 months. Delayed implantation is important to allow pupping and mating to occur when the ice is most developed each year. Spotted seals live for approximately 35 years.

During the spring, spotted seals are usually found in groups of three consisting of a pup, mother, and her mate. The mother will rarely leave the pup when danger approaches but the male will often go in the water and surface nearby. Spotted seals are much more wary after the mating season is over. Large land haul outs where several thousand seals may congregate occur in Kasegaluk Lagoon, Cape Espenburg, and sand bars around Kuskokwim Bay. Large concentrations may haul out on ice as well. Spotted seals are known to make a variety of sounds when they are molting in large groups. The sounds include growls, barks, moans, and roars. When spotted seals move across ice or land it is in a fashion that resembles an inchworm movement that is typical of true seals.   

Predation

Predators known to occasionally prey on spotted seal include sharks, killer whales, walruses, steller’s sea lion, polar bear, brown bear, wolves, several species of birds and of course humans. Spotted seals however do not constitute a significant portion of any of these predator’s diets. They avoid predation by gathering at haul- out areas, being cryptically colored and being agile in water.

Feeding and prey

Adults can dive to at least 300 m, and feed on a wide variety of organisms; composition of diet varies with the age of the seal, and on seasonal variation in abundance of preferred prey species. Newly weaned pups feed on small crustaceans, advance to schooling fishes, larger crustaceans, and octopuses, and finally graduate to higher percentages of bottom dwelling fish species.

Exploitation

As with other Arctic species, the spotted seal is threatened by climate change because their habitat consists of the ice front at the southern edge of the sea ice, an area that may change due to global warming forcing all seal species in the region to redistribute. This may reduce the food resources available or put the seals in closer contact with predators. Oil and gas exploration and extraction in the region may cause disturbance to spotted seal populations as well as environmental contamination of the habitat and food sources due to oil spills. Reduced fish stocks including pollock and herring in the Bering Sea due to commercial fishing may also cause declines in populations of spotted seals as well as other species in the region including Steller sea lions, harbor seals, and northern fur seals. Spotted seals are also caught as by catch by fisheries and some have been killed by fishermen for preying on catches in fishing nets. In Russia, spotted seals are hunted for food to feed foxes on fur farms. Subsistence hunters also kill spotted seals. The annual kill is estimated at 2,500 with a maximum quota of 15,000. In the 1990s about 2,000 spotted seals were killed each year by Alaskan native subsistence hunters, mostly in the Bering Strait and Yukon-Kuskokwim regions.

Commercial hunting of spotted seals has ceased in Japan, although the seals are still hunted there on occasion. Spotted seals also die in salmon trap nets along the Nemuro Peninsula. The spotted seal is listed as nationally endangered in China; it is the only pinniped that breeds in that country. The only spotted seal breeding site in China is found at the Dalian Seal Sanctuary, a nature reserve established in 1992 at Liaodong Bay in the Bohai Sea, however these seals remain at-risk of illegal hunting, entanglement, loss of habitat, disturbance, and reduced food supply.

Threats and status

Subsistence hunting of spotted seals has no doubt occurred since humans made first contact with the species. Intensive harvesting of commercial fish species in the North Pacific and southern Bering Sea poses an as-yet unquantified risk. Entanglement in commercial fisheries occurs in Japan and the Sea of Okhotsk, and fisheries damage control kills regularly occur in small numbers in Japan.

Global climatic change, including global warming, and decreases in annual sea ice development and extent of coverage pose an unknown, but potentially serious, threat to this pagophillic species.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status    

Data deficient (Data in adequate to determine a threat category). 

 

Spotted Seal Mother And In the Bering Sea

Spotted Seal Showing narrow Snout like that of A dog