Name
- English: Insular seal, Kuril seal, Western Pacific harbour seal
- Latin: Phoca vitulina stejnegeri
Family
Insular seal
→ Harbour Seals
→ True seals
| In average | Males | Females | Pups | |
|---|---|---|---|---|
| Length in meters | 1,50-1,80 | 1,20-1,50 | 0,70-0,90 | |
| Weight in kilogram | 55-135 | 45-105 | 9-11 | |
| Life expectancy in years | ||||
| Number of animals nowadays | An estimate of 4.0000 | |||
| Colour(s) | Grey, Brown | |||
| Habitat | From Alaska down south to Hokkaido |
Additional information
The Insular seal belongs to the subfamily of harbour seals, which is probably the most wide-ranging subfamily of pinnipeds . There are five species included in this family. the . The Insular seal is very close related to the Pacific harbour seal , the Eastern Atlantic harbour seal , the Western Atlantic harbour seal and the Ungava seal.
harbour seals have a quite fat body and a narrow-pinched head. The nostrils are narrow and show a typical V-shape. The eyes are quite big and close set to each other. The seals' belly always is lighter coloured than its back. It is difficult to distinguish males from females. The seals' back usally shows varied spots.
The insular seals' fur colour varies from grey to brown. The animals have black spots on their body. The females reach sexual maturity in 3 of 4 years of age. Males reach sexual maturity at six years of age. These seals eat a variety of fish: place, sole, whiting, herring, inkfish, shrimps, mussels.
These seals live along the coasts of the Aleutian and Commaner Islands (Alaska) down south to the Kuril Islands and further to Hokkaido.
Unlike most other pinnipeds harbour seals are generally solitary. They rarely interact with one another. When hauling out they keep spaces of 1 meter or more to each other. These seals are not highly communicative, but when feel threatened they may respond by lunging, scratching, snorting, growling or other aggressive ways of communication.
Although harbour seals are quite solitary they mostly haul out in small groups. The reason is probably for protection from predators. The seals haul out to breed, moult and rest. They haul out on rocky shores, sand beaches, reefs, piers or ice.
Moult takes place in July and August. During the moulting period the seals' metabolism is reduced. They do not eat very much and so conserve energy usually expelled finding food.
The seals give birth during the summer months. Unlike most seal pups the pups moult in their mother's uterus. They are not born with the white pup fur, but have the characteristics of full grown harbour seals. Pups are weaned after 4 weeks. Due to the high percentage of fat in the mother's milk (45%) the pups double their weight by the time they are weaned. The females give birth on flats which get flooded at high tide. From birth on the pups immediately can swim and dive. This is a must, as the flats they are born on are flooded at each high tide. After 2 days the pups can remain undermerged for about 2 minutes. The pups use to leave their place of birth to explore their new habitat.
Mating takes place after weaning. Unlike other mammalians the ovum becomes implantated in the wall of the uterus approximately three months after breeding. This makes it possible to both nurse pups and breed in the short period the seals are together.
During the mating season male seals can become very aggressive. They may fight each other when competing for a female. The males also display aquatic performances and vocalizations to attrack a female. Due to their activities male seals can lose up to 25 percent of their body weight.
Natural predators of the harbour seals are killer whales and sharks. Coyotes and eagles eat juveniles.
Harbour seals usually remain in the vicinity of their traditional breeding area all year round. Due to this restricted range the viability of local harbour seal populations can be particular at risk. For instance the local harbour seal population in the Ontario Lake (Canada) has disappeared in the early 1980's, probably exterminated by human activities. The populations of harbour seals in Greenland (Western Atlantic harbour seal), the Baltic Sea (Eastern Atlantic harbour seal and Western Atlantic harbour seal) and the population in Hokkaido (Insular seal) are cureently under severe threat. The population in the Gulf of Alaska (Pacific harbour seal) has drastically declined in some areas within the last 20 to 30 years.
Fishing nets (especially non-biodegradable nets), plastic wrapping bands and marine debris and threats for harbour seals. Pollutants decrease the productivity and may cause premature parturition. Oil and hydrocarbon are also threathening the harbour seal population. Some seals have been killed by being trapped in the intake pipes of power plants.