The harbor seal, also known as the common seal, is found along the shores on both sides of the north Atlantic and North Pacific Oceans.
There are five recognized sub-species. The western Atlantic harbor seal generally ranges from Greenland and the eastern Canadian Arctic to New England, with some individuals traveling as far south as the Carolinas and even Georgia.
Total population of this sub-species is estimated at 60,000 to 70,000. Because the harbor seal lives in coastal areas, often where there’s heavy vessel traffic, the animal is at considerable risk from oil and hydrocarbon contamination, as well as marine debris.
The adult male ranges from 5 to 5 1/2 feet long and weighs from 200 to 250 pounds. The female is somewhat smaller, at 4 1/2 to 5 feet and 150-200 pounds.
Each harbor seal has its own distinctive color pattern that remains the same from year to year, even through molting. The background color is gray, tan, or brown, ranging from dark to light, and is covered with blotches, spots, and rings of various colors. The thick, short fur is made up of fine, dense underhairs with an overlay of coarser guard hairs.
The seal has a rather small, rounded head with a blunt snout. Its distinctive whiskers are actually sensors that contain blood and nerves.
The eyes are large and adapted for underwater vision, especially in dark or murky water. The harbor seal’s sense of hearing is also much better under the water than on land.
Food and Diet
The diet of a harbor seal varies considerably by season and region. The harbor seals eat fish such as, flounder, hake, herring, rockfish, and salmon as well as squid, and crustaceans.
The harbor seal forages near the shore with a series of relatively shallow dives, each lasting just a few minutes. Harbor seals can stay submerged for up to 30 minutes. They lower their heart rates and conserve energy internally.
While swimming, the wide, webbed rear flippers are used for propulsion, while the smaller front flippers are used for steering.
The front flippers are equipped with claws that can help the seal seize and tear its prey, but the teeth are more often used. The heavy rear molars crush shells and crustaceans and the sharp canines tear other food into chunks. Seals don’t chew their food. They swallow it whole or in large pieces.
In the western Atlantic, mating takes place in middle to late summer. Because it happens in the water, not much is known about harbor seal mating habits, but it appears that males gather in an area and put an aquatic show, with underwater vocalization, to attract females.
Fights between males are very common during this period, and neck wounds are often seen, but fatal injuries are rare. With all the exertion, it’s not unusual for a male to lose as much as 25% of his body weight during the breeding season.
The gestation period is about 10 months. Usually only one pup is born, about 2 1/2 feet long and 12-20 pounds in weight. Pups are normally born with their adult coats, although occasionally a newborn has a white, wooly coat that is shed within a short time. A mother harbor seal usually gives birth on shore, and her pups can almost immediately swim.
A new mother is extremely protective of its pup. She will sometimes carry it on her shoulders or force it beneath the surface of the water to avoid danger.
A pup nurses for three to six weeks before setting off on its own, often traveling a considerable distance before discovering a new habitat.
Harbor seals are mature at 4 to 6 years of age and live for 25-30 years.
Hauling Out and Migration
When they’re not feeding, which takes up as much as 12 hours a day, harbor seals “haul out” in small groups in order to rest and, in season, to molt and breed.
Many different habitats are used for hauling out, including beaches, rocky shore areas, inter-tidal mud and sand bars, and even piers. The ideal hauling out area has easy access to deep water and a food supply, along with protection from heavy waves and wind.
The seals may sleep while they’re hauling out. When sleeping in the water, they assume a “bottling” posture, with the entire body submerged and only the head exposed, allowing them to breathe.
Harbor seals don’t migrate in the traditional sense, but they do follow the food supply, typically heading south during the winter and back north during the summer. In some areas, though, many seals stay throughout the year. This is true, for example, on Long Island, where some harbor seals live their entire lives.