Seal

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Seal
CrabeaterSeal1.jpg
Crabeater seal
Lobodon carcinophagus
Scientific classification
Kingdom Information
Domain Eukaryota
Kingdom Animalia
Subkingdom Bilateria
Branch Deuterostomia
Phylum Information
Phylum Chordata
Sub-phylum Vertebrata
Infraphylum Gnathostomata
Class Information
Superclass Tetrapoda
Class Mammalia
Sub-class Theriiformes
Infra-class Holotheria
Order Information
Superorder Preptotheria
Order Carnivora
Sub-order Pinnipedia
Infraorder Arctoidea
Family Information
Superfamily Phocoidea
Family Phocidae
Population statistics

Seal refers to aquatic mammals of the family Phocidae, which in number of individual species are the largest of the three families of the suborder Pinnipedia. Alternately called earless seals or true seals, they are predominantly found within the polar waters of the Arctic and Antarctica, with several species found in temperate and tropical regions.

Description

Seals on average are generally smaller than the other two families of Pinnipedia (sea lions and walrus), but they include both the smallest and largest members of the suborder. The smallest species are Baikal[1] and ringed seals[2] with lengths between 43.3 and 55.1 inches and a weight of just over 110 pounds. The largest species on record is the southern elephant seal, whose bulls can be 21.3 feet long and over five tons in weight[3]. There is very little sexual dimorphism among the species, with the elephant seals a major exception, as bulls are roughly three times larger than females.

The body shape is designed for effortless swimming. The head is small compared to the body, and noticeably tapers in front. External ears are absent. On the upper lip there are 6-10 rows of whiskers, less rigid than those of the walrus. The tail is short but well pronounced. Front flippers make up less than 25% of body length and are noticeably smaller than the hind ones. The rear flippers are always extended backwards; they do not bend at the hip and cannot serve as a support when moving overland, giving seals a "caterpillar"-like form of locomotion when on land. At sea, however, movement is very fish-like and efficient, with side-to-side sweeps of the rear flippers.

The absolute thickness of the skin of most seals is less than that of the other pinnipeds, while the thickness of their subcutaneous fatty tissue is greater. Thus, in the Weddell seal, the mass of subcutaneous fat is more than 25% of the animal's total mass - about 249 pounds. The sebaceous glands are very large, while sweat glands are less developed than other pinnipeds.

In newborns of a number of species, the fur is soft and thick, often white, and are the animal's first coat for several weeks. In adults the fur is coarse, with no pronounced underfur. Elephant seals are almost completely devoid of hair. The fur color varies among species, sometimes spotted or striped. During seasonal molting, not only the hair is replaced, but also the stratum corneum of the epidermis, which falls off in large sections.

Species

There are 19 species of seal, with one extinction in modern times. Suborder Pinnipedia, Family Phocidae

Range and diet

Most of the species are distributed in cold and temperate waters along coastlines north of 30° latitude in the northern hemisphere, and south of 50° latitude in the southern hemisphere. A few species live in tropical waters, while two inhabit freshwater lakes in Russia, in particular, lakes Baikal[4] and Ladoga[5].

They feed on fish, cephalopod mollusks and crustaceans, and krill[6][7][8]; leopard seals feed on warm-blooded prey, attacking penguins and other seals[9]. Seals can dive very well in search of food, with the Weddell seal reaching depths in excess of 1,800 feet, remaining under water for more than an hour[10][11].

Reproduction

Most seals pair-bond during breeding, while elephant seal bulls have extended harems of 20 or more females which they defend from other bulls[12]. The duration of pregnancy is 270-350 days. Nursing females in search of food swim far into the sea, unlike the female eared seals, which are kept near the shore. Feeding usually stops when the baby is not yet able to feed on its own, and from age 2 to 9-12 weeks it survives on accumulated fat reserves.

References

  1. http://www.conservenature.org/learn_about_wildlife/marine_mammals/baikal_seal.htm
  2. https://www.nationalgeographic.com/animals/mammals/r/ringed-seal/
  3. https://www.nationalgeographic.com/animals/mammals/group/elephant-seals/
  4. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/baikal-seal
  5. http://pubs.aina.ucalgary.ca/arctic/Arctic66-4-417.pdf
  6. https://seaworld.org/animals/all-about/harbor-seal/diet/
  7. https://animalcorner.co.uk/animals/common-seal/
  8. http://www.smru.st-andrews.ac.uk/files/2016/08/Seal-Diet-Leaflet.pdf
  9. http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/leopard-seals
  10. https://www.nationalgeographic.com/animals/mammals/w/weddell-seal/
  11. http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/weddell-seals
  12. http://www.marinebio.net/marinescience/05nekton/esrepro.htm