Biogeography

Caspian seal

April 19, 2011, 3:38 pm
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The Caspian seal (scientific name: Pusa caspica) is one of nineteen marine mammal species of  in the family of true seals. Together with the families of eared seals and walruses, True seals form the group of marine mammals known as pinnipeds.

Physical Description

When Caspian seals are born, they have a coat called a lanugo, made up of long white to silver gray fur. The lanugo helps keep pups warm until they develop blubber. Newborn pups are between 64 to 79 centimetres (cm) in length and weigh about five kilograms (kg) when born. After two to three weeks, the lanugo begins to shed and is replaced by dark gray hair, a process taking six to eight weeks. It is thought that, when pups are weaned at a younger age, they may not mature to be full size adults.

Adult Caspian seals are one of the smallest pinnipeds in the true seal family (Phocidae). Adult Caspian seals vary in size and appearance. Males grow to 1.5 meters (m) in length, which is slightly larger than females, who reach 1.4 m.

Both males and females have grayish-yellow to dark gray fur coats with a lighter underbelly. Males tend to be darker with dark spots over the entire body, whereas females are lighter in colour with lighter spots on the back and not on the belly. The spots of Caspian seals can also be encircled by light colored rings. Both males and females have relatively short flippers with moderate sized claws on their fore flippers and shorter, narrower claws on their hind flippers.

caption Caspian seal. Source:Nano Sanchez
Conservation Status

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Phocidae (True Seals)
Genus:--------- Pusa
Species:--------Pusa caspica (Gmelin, 1788)

Adult Caspian seals have a dental formula of I 3/2, R 1/1, and PC 6/5.

The closest relatives of Caspian seals are Ringed seals (Pusa hispida), the skulls of both species being morphologically similar . However, unlike those of Caspian seals, the bodies of Ringed seals are covered with light rings against a dark background. Both species are similar in size and have a relatively long narrow snout. These two species do not inhabit the same areas, being separated by 1600 km in their global distribution.

Reproduction

Both male and female Caspian seals are monogamous. There appears to be a lack of fighting for a mate among breeding seals.

In late autumn, Caspian seals migrate to the northern part of the Caspian Sea where the water is shallow and frozen. Caspian seals give birth in protected areas on ice sheets after a gestation period of about 11 months. There is no conclusive evidence to support this currently, but researchers believe that, since there is a long gestation period, there is a delay in implantation of the egg.

Annual pregnancy rates are normally between 40 to 70 percent, but are currently at an all time low of 30 percent. This may be due to water pollution. In late January to early February, each female seal gives birth to one pup. Female pups become sexually mature after five to seven years, male pups become sexually mature after six to seven years. Newborn pups are not fully grown until age eight to ten years. Breeding begins a few weeks after the birth of last year's pup, in late February to mid March. Breeding occurs after weaning of newborn pups but can begin while pups are still nursing. After the breeding season and molting in late April, the weather in the north begins to warm, with concomitant ice melting. Caspian seals then migrate back to the southern part of the Caspian Sea. The southern part has deeper, colder waters where seals spend the summer months.

There is little available information about the parental care of Caspian seal pups, except that newborns are weaned after four to five weeks of lactation. Given that Caspian seals are asocial, there may be no collaboration among adults in raising newborn pups. As in the case of their closest relatives, Pusa hispida, as well as other seal species, males leave females soon after mating and fail to assist in rearing the newborn pups. Females will leave newborn pups to forage for short periods of time.

Lifespan/Longevity

In the wild, female Caspian seals live to be on average about 35 years old; however, some have been recorded to live 50 years. Males have relatively short lives, around 26 years. Caspian seals are not usually found in captivity, except for a few zoos in Russia. There is a lack of data to document their life span in captivity.

Behaviour

Caspian seals tend to live in large groups during the mating season in summer and winter months. At other times of the year, these seals are solitary. Caspian seals are shallow divers, typically diving 50 meters for about one minute, although scientists have recorded Caspian seals diving deeper and for longer periods of time. After foraging during a dive, they rest at the surface of the water.

Little is known about communication among Caspian seals. They are solitary in winter months, in summer months they make aggressive snorts or use flipper waving to alert other seals to keep their distance.

Distribution

Caspian seals, are one of the most numerous and widespread of northern pinnipeds. They are only found in the world’s largest inland body of saltwater, the Caspian Sea, which is located in a small part of the Paleartic region, between the countries of Russia, Azerbaijan, Iran, Turkmenistan, and Kazakhastan.

Caspian seals migrate to different parts of the Caspian Sea during different seasons; however, they never leave the landlocked Caspian Sea. From May to September most Caspian seals reside in the southern part of the Caspian Sea. In autumn, they migrate north to the ice sheets for breeding and birth of their newborn pups.

There are various ideas to explain how Caspian seals began inhabiting the Caspian Sea. One theory is that they are direct descendants of Ringed seals (Pusa hispida). During the Quaternary period during the present Ice age, when there were glacier ice sheets, Ringed seals migrated south. When the ice retreated seals were left isolated in the Caspian Sea. Others argue that Caspian seals originally occupied an inland area of the Paratethys Sea during the Miocene and Pliocene epochs. Other researchers argue that ringed seals are derived from Caspian seals and eventually migrated north to the Arctic.

Habitat

Caspian seals live in the temperate region of the Caspian Sea on islands or fast ice sheets. This landlocked, saltwater sea is 31 metres below sea level at latitudes of 37 to 47 degrees north. Caspian seals can also be found in estuaries along the Caspian Sea. The mouths of the Volga and Ural rivers are the most popular of these estuaries.

During winter months Caspian seals live at the northern reaches of the Caspian Sea on ice caps. There, females give birth and nurse their young. A small portion of the population breeds farther south in the winter on islands such as Ogurchinsky, near the Turkmenistan coastline.

These breeding areas tend to be in protected places like pressure ridges away from wind and predators. Unlike their closest relatives, Ringed seals (Pusa hispida), Caspian seals do not give birth in lairs (holes in snow drifts); this behaviour is likely an adaptation to ice that is not as stable as Arctic ice.

During the spring and summer months, Caspian seals migrate south to live on sand banks or rocky areas, usually on islands and usually not on the main coastline. The southern part of the Caspian Sea has deeper water where the Caspian seal may dive to depths of 50 meters.

Predators

The Caspian seal is the only mammal found in the Caspian Sea, and this species is near the top of the food chain. They consume many different types of fish and crustaceans; correspondingly, If seal populations decrease, fish populations may increase. Seal population density may also affect the numbers of their two predators (besides humans), sea eagles (Haliaeetus leucoryphus) and wolves (Canis lupus). Sea eagles snatch up newborn pups soon after they are born; consequently, during lactation pup mortality rate approximate 22%. In the northern part of the Caspian Sea, wolves prey upon Caspian seals lying out on islands.

Food Habits

Caspian seals are primarily piscivores, who consume a variety of fish species depending on season and availability. Clupeonella (kilka) is the most abundant food source in the Caspian Sea, accounting for 70 percent of their diet. When Caspian seals inhabit shallow waters in the northern part of the sea (autumn and winter months), they prey mostly on sculpins, gobies, and crustaceans. While in the deeper waters of the southern Caspian Sea during the summer months, they eat herring, roach, carp, sprat, and smelt. When Caspian seals are found in estuaries, they eat large amounts of the freshwater species Stizostedion lucioperca. Other prey include shrimp, crab, silversides, and asp.

Conservation Status

They are listed as Endangered on the IUCN Red List of Threatened Species. This is for several reasons: loss of prey to commercial fishing, toxic pollution, habitat destruction, human disturbance, disease and commercial exploitation. In addition to a few regulations limiting the amount of Caspian seals caught each year, adult females are also protected during the breeding season.

Economic Importance for Humans

For the past 200 years, humans living around the Caspian Sea have killed seals for their blubber and for the lanugo fur of newborn pups. Currently around 60,000 Caspian seal pups are slaughtered annually for their fur. Some ecotourism is increasingly focusing on these animals, which involvesferry trips for viewing.

Hunting Caspian seals in the past has been intense. For example, between 1933 and 1940 an average of 160,000 seals were taken annually. In 1940, when the hunting of Caspian seals was first regulated, there was still an average of 50,000 to 60,000 caught each year. In 1970 restrictions were increased on the northern ice allowing only 20,000 to 25,000 pups to be killed annually. However, when the Soviet Union collapsed, these regulations were not enforced; in fact, the weakened Soviet Union contributed to a large increase in illegal killing and poaching of Caspian seals.

Caspian seals do not negatively affect humans. They may consume certain fish, but these species are not typically economically important.

Further Reading

  1. Pusa caspica (Gmelin, 1788) Encyclopedia of Life (accessed July 22, 2010)
  2. Pusa caspica, Easley-Appleyard, B. and P. Myers., 2006, Animal Diversity Web (accessed July 22, 2010)
  3. Caspian seal, Seal Conservation Society (accessed July 22, 2010)
  4. Pusa caspica IUCN Red List of Threatened seals, (accessed July 22, 2010)
  5. The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
  6. Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
  7. Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
  8. Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899

 

Glossary

Citation

Life, E. (2011). Caspian seal. Retrieved from http://www.eoearth.org/view/article/150951

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