Harbor Seal
Habitat And Distribution
 The harbor seal, P. vitulina richardsi, is found along the Pacific
coast of North America with distribution throughout the eastern Pacific
ranging from the Pribilof Islands to Baja California, Mexico. The
northernmost portions of their range in the Bering Sea include Bristol Bay,
the Pribilof Islands, and the Aleutian and Commander Islands. The
southernmost limits are Hokkaido, in the west and Cedros, Natividad, and the
San Roque Islands, Baja California, in the east.
Photo by Tim Ayler
There are approximately 40,000 harbor seals in California waters. They
can usually be observed inhabiting shallow areas where sandbars, rocks and
beaches are uncovered during low tides or otherwise easily accessible.
Since harbor seals do not migrate, in many areas they are present year-round
and while site fidelity is displayed, harbor seals are also capable of
long-distance movements. Some short movements may be associated with
seasonal availability of prey and with breeding.
General Characteristics
Males: 1.4 to 2.0 m long and 70 to 170 kg
Females: 1.2 to 1.7 m and 50 to 150 kg
Harbor seals are not sexually dimorphic; no significant differences in size
between females and males.
Body is fusiform with the neck moderately long, thick, and not distinctly
pointed. The head is rounded and short.
The snout is blunt and because harbor seals spend so much time underwater
its nostrils are naturally shut giving them their characteristic V-shaped
nostrils. They must actually be pushed open when inhaling occurs. All
pelvic bones are fused prohibiting independent movement of the hind quarter.
Hind quarter cannot be rotated under their bodies. Multiple layers of
blubber provide insulation, buoyancy, and energy reserves.
 Harbor Seal Coat
The fur on a harbor seal is short and thick, consisting of coarse guard
hairs and finer, denser underhairs. Its pattern is similar to a
human's fingerprint; unique to the individual. The patterns range from
light coats (white, silver, light gray) with dark rings or spots, to medium
coats (beige, brown) with light or dark rings, or dark coats (dark gray,
black) with light rings. The hair itself provides no insulation.
Instead, glands in the skin secrete oils that protect the coat.
Because of this, harbor seals must molt annually. Molting occurs after
every breeding season. In the arctic, pups will be born with a white coat
called the lanugo and will molt this coat shortly after birth. In
regions where ice is not present, this coat will be shed in-utero.
Some harbor seals display signs of iron oxidation known as "red pelage."
Iron oxidation or red pelage is a condition that causes the hair of certain
seals to turn red. There appears to be no physiological effect on the seals,
according to D.G. Moser of the Moss Landing Marine Laboratories. The
condition is thought to be caused by an accumulation of iron on the outer
surface of the animals’ hair. Moser found that the hair of red pelage
animals was very high in cuticle degradation and speculates that the
affected animals’ fur may have physical properties allowing iron or other
elements to oxidize on the hair.
Limbs
Limbs composition is extremely similar to terrestrial mammals in that they
share the same basic bones. However, in harbor seals, the structure is
modified into extremely short flippers, fore and hind, that are covered with
hair and posses claws as long as 5 cm. The foreflippers are not severely
webbed, and therefore not used for propulsion. The hindflippers are broader
than the foreflippers and are significantly webbed allowing water
resistance, which is used for propulsion.
Tail
Not easily seen, harbor seals have a short, flat tail located between the
hind flippers.
 Senses
Hearing
Harbor seals, like all true seals, lack an external ear flap, but do have an
external pinnae, or opening to the ear canal that provides them with a keen
sense of hearing, responding to underwater sounds from up to 180 kHz.
In the air, hearing is reduced with a response range up to 22.5 kHz.
Eyesight
Harbor seals' eyes are prominent and adapted for shades of black and white. Color vision is not necessary and therefore is probably poor to
non-existent. Compared to humans, they have superior vision underwater, yet
inferior vision on land. To protect the eyes while out of the water, mucus
continually washes over them. Since pinnipeds lack a duct for
draining eye fluids into the nasal passages, these fluids drip out of the
eye and give the seals their characteristic wet spots surrounding the eyes.
Good vision does not seem to be essential to harbor seal survival;
scientists have found blind but otherwise healthy individuals, including
mothers with pups, at sea. Photo by Kelly Gara
Tactile
A harbor seal uses its sensitive vibrissae to detect vibrations. They
thrust the vibrissae in a sweeping movement by pushing their mobile upper
lip in and out. When vibrations are detected, a substantial nerve
system transmits tactile information from the vibrissae to the brain.
Thermoregulation
Harbor seals have a metabolic rate higher than that of a comparable land
mammal, allowing it to generate a greater amount of body heat. Heat loss is
prevented by a thick layer of blubber, which not only insulates the seal,
but can be metabolized for energy as well. An additional benefit of blubber
is that it provides a heat gradient from the body's core to its skin.
This allows the seal's skin to be approximately the same temperature as the
surrounding water while its core temperature remains approximately 100 deg
F.
In cold water, blood vessels constrict (contract), slowing the flow of blood
to the skin and therefore, reducing heat loss to the environment. When
hauled out, the process is reversed and blood vessels dilate (expand),
allowing heat to be released to the environment.
Communication And Vocalization
Harbor seals are thought to be the least vocal of all pinnipeds, vocalizing
only for defense. Harbor seals are often observed during the pre-mating and
mating seasons slapping the water with their pectoral flippers as a form of
communication. They may also perform this behavior to show aggression.
 Land Movement, Swimming, And
Diving
LAND MOVEMENT
Since harbor seals cannot rotate their hind flippers underneath the pelvic
girdle, when on land they move by undulating in a caterpillar-like motion.
SWIMMING
Hind flippers move in a side to side motion to propel their bodies.
Foreflippers act as a rudder. They can swim up to 19 kph.
DIVING
Harbor seals can dive to depths of 90 m and stay submerged for 15 to 28
minutes. Mean dive duration is directly proportional to seal
size, with larger seals averaging longer dives. External ear openings
close when diving. Physiological adaptations for diving include:
slowing of the heart rate from 75 to 120 beats per minute to only four to
six beats per minute, slowing of the metabolic rate, dropping the body
temperature, tolerating high carbon dioxide levels, and collapsing the lungs
before diving. Further, to conserve oxygen underwater, a harbor seal
has a greater volume of blood than land mammals of the same size; therefore,
it can retain more oxygen. Additionally, the muscle of harbor seals also has
a high content of the oxygen-binding protein myoglobin (about 10 times as
much as humans). Myoglobin stores oxygen and helps prevent muscle oxygen
deficiency. Photo by Paul Riley
Diet And Feeding Habits
Harbor seals are opportunistic feeders, primarily consuming bottom dwelling
and schooling prey. Common prey species include herring, flounder, and
perch. They will also consume octopus, squid, and shrimp. A harbor
seal's diet varies seasonally and regionally and often is subject to local
prey availability. Harbor seals generally obtain the water they need
from their food. If food intake is decreased, the metabolic breakdown of fat
produces water. Dehydration usually follows illness or injury.
Reproduction
 Birth
The timing of birth varies with latitude. Generally, it occurs between
February and June. Females generally give birth to one pup each year.
Multiple births are extremely rare, but twin fetuses have been documented.
The problem with twining is that the mother cannot physically support two
pups. When two pups are born only the healthiest is cared for, the
second is left to die. Surrogate females has been noted, but they are
extremely rare.
Gestation
Gestation is one year with a period of delayed implantation. There is
actually only 9-10 months of fetal development.
Pups
Pups are born at approximately 20-24 lbs. and are approximately two feet
long. In California waters, the lanugo coat is usually shed in utero
and the pups are born with a spotted coat.
Hauling-Out Trends
Although they assemble in groups of up to several hundred, they do not form
breeding colonies. There are currently more than 300,000 harbor seals along
the Pacific Coast, which haul out regularly. Factors influencing
haul-out behavior include season, time of day, tide, wave height or
intensity, wind chill, and disturbance. Good visibility and quick access to
deep water seem important features of a haul-out location. Harbor seals
often haul out onto land, during the times when human disturbance is the
least. Spending much of their time on land, they can be observed on
river banks, beaches, offshore reefs, rocky points and on manmade artifacts
such as buoys and docks. They rarely move from one location once hauled-out;
however, they remain alert and will scan the area frequently. They
often choose to rest where the tide is changing and let the water wash over
them allowing themselves quick access to the water in case of a threat.
Harbor seals hauled-out often assume a characteristic banana shaped profile.
Unlike elephant seals, harbor seals generally do not touch each other when
hauled out. If other individuals come too close, they respond with
growling, snorting, aggressive flipper-waving, head-butting, scratching, or
biting. Fighting is rare, except between competing males during the
mating season.
Source: Palomar College
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