Common seal
- The common seal is born without a white embryonic coat, unlike other seals that are born on ice. In coastal forms, this coat disappears in the last days of pregnancy.
Age
Common seals, also known as harbor seals or common seal harbour seal, have a typical lifespan of from 15 to 30 years, with a maximum recorded lifespan of 47 years and 8 months, and a theoretical lifespan ranging from 23 years and 10 months to 47 years and 8 months; the age of sexual maturity ranges from 3 to 6 years. The young are born with their eyes open, and during the embryonic stage, the fetus develops inside the mother, receiving nourishment via the placenta and not eating independently. A newborn pup lives on the shore or an ice floe, feeding on the mother’s rich milk and growing rapidly, for a duration of from 1 day to 4 weeks. The adult stage begins after this period and lasts from 4 to 35 years, during which the species lives in the sea, coming ashore only for rest, molting, and giving birth, actively hunting and capable of diving to great depths.
Phenotype
Embryo: Body color— The embryo's body is formed inside the uterus. By the end of the gestation period, it is covered with fine fur. Calf: Fur— Thick and soft fur helps to retain heat on land and in water. Calf: Number of whiskers— Sensitive whiskers help the calf to navigate in water after entering the sea. Adult: Body color— A streamlined body without external ears allows for fast swimming and diving. Adult: Number of flippers— Flippers are used for swimming and movement on land; the hind flippers help with steering. Adult: Number of teeth— Sharp teeth capture and hold slippery fish. Adult: Number of whiskers— Long sensitive vibrissae help to find fish even in darkness.
Physiology
The common seal is a species characterized by significant variations in body size; body height can reach from 17.8 cm to 4.5 m, and body length from 1.4 to 1.9 m. The mass of an adult animal varies from 67.98 to 88.45 kg; however, at different stages of development, indicators of body mass and length differ significantly: at the "Embryo" stage, body mass is from 4 to 8 kg, and length is from 40 to 60 cm, at the "Pup" stage – body mass from 8 to 16 kg, body length from 80 cm to 1 m, and in an adult seal, body mass fluctuates from 80 to 170 kg, with a body length of from 1.5 to 1.9 m.
Habitat
The common seal inhabits the river mouth in the sea where the water is slightly salty and rich in fish and birds, as well as shallow waters near the shore where the water rises and falls, and crabs live. The species prefers marine environments, coastal waters, the benthic coastal zone, and the near-bottom coastal zone. The common seal's habitat is associated with cold seas where there may be ice in winter and it is not hot in summer, as well as conditions of constant humidity. The species is found in temperate seas where the water is cool or warm, it is cold in winter, comfortable to swim in summer, and in zones with a warm summer and abundance of rains, as well as in places with a warm summer and not very cold winter.
Shelter
Common seals inhabit sandy and rocky shores, shallows, and ice floes; the species does not have a permanent or long-term shelter. They do not use a fixed den, and the purpose of these locations includes protection from predators, breeding, molting, and resting.
Geography
Common seals or harbor seals occupy the Nearctic realm, the Palearctic realm, and the marine realm. The species’ ecosystems include the Gulf of Alaska, the North Sea, the Celtic-Biscay shelf, and the Northeast continental shelf of the United States.
Feeding
The common seal primarily eats fish, hunting in water and catching prey with sharp teeth, and sometimes consumes squid and crustaceans, including shrimp. The species employs an active hunting strategy to obtain food, which includes carp-like fish, catfish-like fish, salmon-like fish, herring-like fish, flounder-like fish, toothcarp-like fish, characin-like fish, pike-like fish, eels, sculpin-like fish, and Sargassum fish. The daily food requirement ranges from 3 kilograms to 6 kilograms, while the young consume milk. In some cultures, the animal is eaten, but it is not considered halal or kosher.
Reproduction
The common seal reproduces through live birth, with the female giving birth to one pup on land or ice. The gestation period is 8 months and 2 weeks, and the female has one pup per litter. Young harbor seals are fed milk for approximately four weeks, and reproduction occurs once a year. The interval between reproductions ranges from 11 months to 1 year. The species inhabits and develops on land, outside of bodies of water, with eggs, larvae, or young developing in nests built on the ground or close to it. These nests are located directly on the surface of the ground. Individuals reach sexual maturity from 3 to 6 years of age, and reproduction always involves fertilization without generational change.