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Deepseawaters
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Harbor Seal
Harbor Seal
Common Name: Harbor Seal
Scientific Name: Phoca vitulina
Description
Harbor
seals
are mammals, that is they are hairy, warm-blooded, air-breathing
animals which suckle their young. They weigh about 24 pounds
(11 kg) at birth and gain weight rapidly during a month-long
suckling period, perhaps doubling their weight. Average weight
for adults is about 180 pounds (82 kg); males are somewhat
larger than females. They are covered with short, stiff, bristle-like
hair. Coloration varies, but two basic patterns occur: a dark
background with light rings, or light colored sides and belly
with dark blotches or spots. Harbor seals molt annually,
usually in late summer.
Harbor
seals are well adapted to life in the sea. They are able to
dive to depths exceeding 600 feet (183 m) and can remain submerged
for over 20 minutes. Oxygen-conserving adaptations that allow
such dives include reduced peripheral circulation, reduced
heart rate, and high levels of myoglobin (muscle oxygen binder).
Harbor seals are graceful and efficient swimmers
as they use their hind flippers for propulsion and foreflippers
as rudders. Movement on land, however, is slow and laborious.
The
harbor seal (Phoca vitulina), a widespread
species in both the north Atlantic and Pacific oceans,
is found in Alaska along the coast from British Columbia north
to Kuskokwim Bay and west throughout the Aleutian Islands.
Harbor seals are often called "hair" seals
by coastal residents of southern Alaska. Most harbor seals
are associated closely with coastal waters, although occasional
observations up to 50 miles (81 km) offshore have been made.
One radio-tagged animal crossed 45 miles (72 km) of open ocean
between two islands in the Gulf of Alaska, and another moved
over 50 miles (81 km) from Prince William Sound to Middleton
Island. Harbor seals haul out of the water
periodically to rest, give birth, and nurse their pups. Reefs,
sand and gravel beaches, sand and mud bars, and glacial
and sea ice are commonly used for hauling sites. Harbor seals
are sometimes found in rivers and lakes, usually on a seasonal
basis (present in summer, absent in winter). At Iliamna Lake
seals are present year-round and are probably resident. Births
of harbor seal pups are not restricted to a few major
rookeries (as is the case for many species of pinnipeds) but
occur at many hauling sites.
Harbor
seals do not appear to make long annual migrations
like some species of marine mammals. However, considerable
local movements occur. Tagging studies have shown that juveniles
move up to 150 miles (242 km) from their birth places. A radio-tagged
adult was discovered 120 miles (193 km) from its tagging site.
As more seals are being satellite-tagged, much more information
is becoming available about winter and summer movements.
Harbor Seal Facts
Winged
Foot-
The harbor seal is the only pinniped that
breeds along Puget Sound. Pinnipeds (seals, seal
lions, and walruses) spend part of their lives in the water
but depend on land to give birth and raise young. The term
"pinniped" comes from the latin word "pinna"
meaning winged and "ped" meaning foot.
Small & Spotted- Adults are mottled tan
or blue-grey with dark spots, measuring between four and
seven feet long, weighing 250 to 300 pounds. To distinguish
harbor seals from other pinnipeds along Puget Sound (California
sea lions, Northern sea lions, and elephant seals)
look for the harbor seal's small size, earless head, and
spots.
Deep Diver- The harbor seal
can plunge 300 feet and stay underwater up to 28 minutes.
It can swim a fast 15 knots.
White Before Birth- Most harbor
seal pups shed a white wooly coat before they are
born. Sometimes pups are born in the water. Pups can often
swim after birth, when the tide returns.
How to Identify Harbor Seals
 The
harbor seal, northern fur seal, California sea lion,
Steller sea lion and northern elephant seal
are the five species of pinnipeds a visitor might see at Point
Reyes. Harbor seals can usually be distinguished
from elephant seals by size alone. The harbor
seal is a rather small marine mammal, only
getting up to 1.5-1.8 m (five-six feet) in length and 115
kg (250 pounds) in weight, whereas elephant seals are much
larger. Bull elephant seals average about 1,360 to 2,500 kg
(3,000 to 5,500 pounds), while females range in weight from
360 to 545 kg (800 to 1200 pounds). However, yearling and
weaned pups weigh about 135 kg (300 pounds), so a young elephant
seal could be mistaken for an adult harbor seal, if one attempts
to identify the seal by its size. What color is the seal?
While young elephant seals are a uniform gray, harbor seals
are typically silver, white or gray, with black spots, although
some harbor seals also are black or brown with white spots.
Sometimes a harbor seal may have a reddish colored head or
body, which is due to iron oxide deposits on the hair shafts.
Harbor
seals and elephant seals are in
the Family Phocidae (the earless seals) so unlike sea
lions and fur seals, they do not
have external ear flaps on the head, just a small hole where
their ear is. Harbor seals and elephant seals also
are unable to rotate their pelvis, and so they drag their
body inchworm fashion around on land, on beaches, or other
nearshore substrates that have a low slope. Sea lions,
in contrast, can rotate their pelvis forward and walk on all
four limbs, enabling them to use steep, rocky shoreline habitat
unavailable to harbor seals. Harbor seals
also differ from sea lions in their smaller size and lighter
color. When in water, harbor seals propel themselves with
their hind flippers in a sculling motion, and steer with their
front flippers, whereas sea lions and fur
seals propel themselves with their fore-flippers,
like wings.
Life History
The
young pups are able to swim almost immediately after birth.
They normally remain with their mothers about one month, after
which they are weaned and separate from their mother. At that
time over half their body weight may consist of fat, providing
them a head start on self-sufficiency. Sexual maturity occurs
at between 3 and 7 years. Mature females mate shortly after
the weaning of their pups; however, the embryo does not implant
in the uterus until about 11 weeks later, a trait called delayed
implantation. Active fetal development is about 8½
months.
The
sex ratio of harbor seals at birth is approximately equal
and remains so until about 5 years of age. Thereafter mortality
rates for males are higher, and females become relatively
more abundant. Maximum ages estimated from annual rings in
their teeth are 26 years for a male and 32 years for a female.
Diet
Commonly
eaten prey include walleye, pollock, Pacific cod, capelin,
eulachon, Pacific herring, salmon, octopus, and squid.
Harbor
seals are within the Order Carnivora, which means
that they primarily eat meat. The meat they eat is fish in
the nearshore waters of the park, such as herring, anchovies,
sardines, hake, flounder, sole, salmon and sculpin. They
also eat invertebrates such as octopus and squid and even
crabs. The harbor seal is considered an "apex predator"
because it feeds towards the top of the food chain. Apex predators
are often used as an indication of the condition of their
ecosystem because they can't do well unless all of the organisms
within their habitat are doing well. Point Reyes has been
using the harbor seal as one of the indicators of the condition
of the area's marine systems. The population has grown and
stabilized over the past decade and females give birth to
pups around every year. During El Nino years, though, female
seals often skip giving birth and the population counts onshore
are lower, likely because seals are spending more time in
the water looking for food.
What Eats Harbor Seals?
White
sharks
are the primary marine predator of harbor seals, but occasionally
other large sharks and killer whales eat
them. Terrestrial predators such as coyotes and bobcats can
also occasionally prey on harbor seals resting onshore, particularly
pups that are very young.
Rarely,
male elephant seals have been documented
killing harbor seals in California at harbor seal
colonies such as Jenner. This elephant seal behavior
is very unusual, and the male seals do not appear to interact
or haul out with other elephant seals. Instead, they haul
out at harbor seal colonies.
Hauling Out
Harbor
seals (and sea lions) haul out
(come out of the water) almost daily to rest and to warm up.
They cannot maintain their body temperature if they stay in
cold water all the time because of their smaller size and
thinner blubber layer. Northern elephant seals
lose less heat than harbor seals because
are much larger and have a thicker blubber layer that allows
them to stay at sea for months at a time before coming onshore
to rest and give birth.
All
pinnipeds give birth on land, and that is one fact that distinguishes
them from cetaceans, another group of marine mammals. Harbor
seals give birth between March and June on tidal
sandbars, rocky reefs and pocket beaches. They can give
birth on areas which are inundated at high tide because harbor
seal pups, unlike most pinniped species, can swim at
birth. During the pupping season, mother seals will spend
more time onshore nursing pups and resting, for an average
of around 10-12 hours per day. The mother harbor seal stays
with the pup almost continuously and rarely leaves the pup
alone onshore. Mothers can take their pups with them when
they go swimming and feeding because pups are adept swimmers.
A
mother caresses and nuzzles its baby pup constantly, and for
four to six weeks nurses it with her rich milk. The 48% fat
content of milk makes the pup gain weight rapidly, and by
around 30 days they are weaned. Pups weigh around 11 kg (25
lbs) at birth but when they are weaned they may weigh as much
as 22 kg (50 lbs).
During
the breeding season, male seals hold territories in the waters
adjacent to where females haul out on shore, called maritory.
Females are receptive to mating around when the pups are weaned
and mating occurs in the water. Male seals will protect their
maritory from other males and engage in stylized fighting
during the breeding season.
Shortly
after the pups are weaned, the seals begin their annual molt
of their sea worn fur. The fur sheds much like a dog and the
seals turn a luminous color with new fur. The molt period
begins around mid-June and extends through July. During this
time, seals will spend more time resting onshore because it
is energetically taxing. Also, studies have shown that hair
follicles grow faster in onshore than in the water. Seals
can stay onshore resting for an average of 12 hours per day
during the molt compared to around 7 hours per day during
fall-winter months.
Abundance and Trends
Harbor
seals
are a difficult species to census because they can be accurately
counted only when they are hauled out. They
haul out in thousands of locations in Alaska, and even if
seals at all sites could be counted, the proportion of the
total population hauled out at any given time is unknown.
The total Alaska harbor seal population probably
ranges between 200,000 and 300,000 animals. Since implementation
of the Marine Mammal Protection Act in 1972, hunting has been
restricted to Alaska Natives. In some areas, harbor seals
are an important part of the subsistence economy. The annual
harbor seal harvest is about 2,500 to 4,000 animals.
The
number of harbor seals has declined in several
areas of the Gulf of Alaska and Prince William Sound since
the mid 1970s. At Tugidak Island near Kodiak, numbers have
declined 90 percent from approximately 11,000 seals to 1,000.
The reasons are unknown
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