Harbor seals, Phoca vitulina, may be the most commonly spotted seal on
Stellwagen Bank. Highly adaptable and widespread, they are found in the
subarctic and temperate areas of the Pacific and Arctic oceans.
At sea, harbor seals are usually found alone or in small, very loose
groups that reduce competition while foraging. On Stellwagen Bank, it is
believed that they feed mostly on sand lance and herring. On land, they often
gather at low tide on sandy or rocky beaches, preferably islands, where they can
scan the environment for danger.
A female harbor seal hunting sand lance.
Harbor seals are relatively small (1.5 meters, or 5 feet long), with a coat that
varies somewhat with age, wetness and between individuals. Some pups are born
with a light colored, lanugo coat (fetal fur that most mammals shed before
birth). The lanugo coat is shed within a few weeks of birth. Most seals, though,
are born with an adult coat that darkens with age.
Females in this area usually give birth in late spring and early summer. It is
thought that females from Massachusetts migrate to quiet islands in New
Hampshire and southern Maine to pup. Historically, harbor seals pupped in
Massachusetts, and there are increasing sightings of very small pups here in May
and June. Pups are able to swim within minutes after birth and can travel with
the female while she hunts. On Stellwagen, small pups are often found treading
water while waiting for mom to return from a dive.
Adults of both sexes are similar in appearance, with lighter undersides, brown
to gray topsides and differing amounts of irregular spots throughout. Harbor
sealsí front flippers have relatively small claws, and the claws of their hind
flippers are tiny. At sea, they can be hard to spot. Only their heads are
visible as they come up for air, their snouts are small and pointed, and they
have a small but definite brow. If you have binoculars, you can spot ear
openings just behind the eyes.
Gray seals, Halichoerus gypus, are the largest seal found in the area, with
males growing to 8 feet and weighing over 900 pounds (2.3 m. and 300-350 kg.).
Females are somewhat smaller, measuring 7 feet and weighing less than 600 pounds
(2 m. and 150-200 kg.). Besides size, the sexes differ in a number of ways:
males tend to be darker with few light spots, while females tend to be light
with dark, irregular blotches. Young can be easily confused with harbor seals.
With a head-on view, gray seals have wide-set nostrils that form a W, while
harbor seals have close-set nostrils that form a small V. Sometimes called
horseheads, gray seals of both sexes have broad, long snouts that become more
pronounced, especially in males.
Profiles of male and female gray seals.
Gray seals are endemic to the North Atlantic, ranging from the Baltic,
western Europe to Canada and Northeastern United States. In recent years, the
number of gray seals in New England seems to have grown. It is not yet clear if
the Canadian population is simply growing and moving south, or if there are
other, environmental factors at work.
Highly gregarious, gray seals are often found in large groups hauled out on
quiet sand or rock beaches for rest and breeding. Females in this area, such as
Monomoy Island in Nantucket Sound, give birth to one, white-coated pup from late
December to mid February. The pup is nursed intensively for about 15 to 20 days
on an increasingly fatty milk. Females come into estrus about 2 weeks after
weaning their pups. Males are highly competitive over access to groups of
females on shore. After fertilization, the embryo stops development and "rests"
for 3 to 4 months before development resumes (delayed implantation).
Above: first year harp seal hauled out - notice spotting.
Below: adult harp seal - notice dark face and sides.
Unspotted coat of a "blueback": juvenile hooded seal.
Note the blunt-nosed profile and
dark face of juvenile hooded seal.
Profile of a ringed seal.
Harp seals, Pagophilus groenlandicus, grow to about ameter and a half, weighing about 130 kg. (5.5 feet and 280 pounds). Usually they
have light gray or white coats marked with dark brown patches about the head and
back. These dark markings may form a U on the back, much like the base of a hand
held, musical harp. Young animals go through a complicated series of molts,
changing from infant "whitecoats" (principal aim of the annual Canadian seal
hunt) to "bedlamers" and "spotted harps" of the juveniles.
Despite the fact that harp seals are considered a northern species, dependent
upon pack ice habitats for pupping, sightings of juveniles in the southern Gulf
of Maine have increased in the last decade, during the winter months. Sightings
of adults are less common but increasing.
Hooded seals, Cystophora cristata,are somewhat sexually dimorphic in size, with males reaching 2.5 m. and 300 kg.
(8 feet, 600 pounds) and females reaching 2m. and 160 kg. (7 feet, 350 pounds).
In form though, the sexes are quite different: males have an inflatable sac
drooping from the top of the nose. When inflated, it forms a black, oval hood.
Further, they can inflate the red, inner lining of the nose out of one nostril.
This spectacular display may be used to reduce actual fighting during conflicts
with other seals. Adults are silvery blue or white with irregular dark brown
patches. Juvenile stages include the handsome "blueback" of first year animals:
bluish gray on the back, cream colored belly and dark flippers and mask.
In this area, hooded seals are a rare sight. They share much of their range with
harp seals but give birth on pack ice, a little later (last two weeks of March).
Young are nursed for a mere four days and may double their birth weight by
weaning. Most sightings locally are of the young of the year.
Ringed seals, Phoca hispida,
are the smallest seal to make an appearance in this area at about 1.5 m. long
and 70 kg. in weight (4.5 feet and 150 pounds). Males and females differ little
and their mass changes radically throughout the year, especially during the molt
when animals are unable to feed. They are generally dark gray above and cream
below with a constellation of light rings scattered across the head and
back.Their front flippers are short and strong, outfitted with long, curved
These small stocky seals are true ice seals, rarely straying far from ice
habitats in the Arctic and Subarctic. Adults especially prefer land-fast ice and
juveniles stray out to the fringes and pack ice. Their long claws allow ringed
seals to keep breathing holes open through the ice. Young may wander far and
each year a few come ashore on Cape Cod to rest, especially during the winter
months. Despite these appearances, ringed seals play only the most minimal role
in the ecology of Stellwagen Bank.
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