HARBOR SEAL FACT SHEET

WITH EMPHASIS ON

Phoca vitulina richardsi

 

CONTENTS

I.  CLASSIFICATION

II.   HABITAT AND DISTRIBUTION

III.   GENERAL CHARACTERISTICS

IV.  PELAGE

V.  LIMBS

VI.  TAIL

VII.  SENSES

VIII.   THERMOREGULATION

IX.   COMMUNICATION AND VOCALIZATION

X.  LAND MOVEMENT, SWIMMING, AND DIVING

XI.   DIET AND FEEDING HABITS

XII.  REPRODUCTION

XIII.  HAULING-OUT TRENDS

 

I.  CLASSIFICATION

Order - Pinnipedia

Family - Phocidae

Genus, species - Phoca vitulina

Subspecies - richardsi  

Common name -harbor seal, common seal

II.  HABITAT AND DISTRIBUTION

The harbor seal, P. vitulina richardsi, is found along the Pacific coast of North America with distribution throughout the 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.

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. 

III.  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 is 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.

IV.  PELAGE

Pelage 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 which 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.

V.  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.  

VI.  TAIL

Not easily seen, harbor seals have a short, flat tail located between the hind flippers.

VII.  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 is better, yet inferior 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.

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 form the vibrissae to the brain.

VIII.  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.

IX.  COMMUNICATION AND VOCALIZATION

Harbor seals are thought to be the least vocal of all pinnipeds, vocalizing only for defense.

A 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.

X.  LAND MOVEMENT, SWIMMING,  AND DIVING

LAND MOVEMENT

Since harbor seals cannot rotate its hind flippers underneath the pelvic girdle, when on land they move by undulating in a caterpillar-like motion.

SWIMMING

Hindflippers 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.

They characteristically sink slowly dive.

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.

XI.  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.

XII.  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 2 feet long.  In California waters, the lanugo coat is usually shed in utero and the pups are born with a spotted coat.

XIII.  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 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.

REFERENCES

1. American Cetacean Society (ACS) Monterey Bay Program Summary. 1996.

2. BRASSEUR, S., CREUWELS, J., WERF,B., AND P. REIJNDERS. 1996. Deprivation indicates necessity for haul-out in harbor seals. Marine Mammals Science 12(4):619-624.

3. FICHTER, G. 1990. Whales and other Marine Mammals. Golden Press. Racine, Wisconsin. 160 pages.

4. PAUL, B.D., AND J.M. TERHUNE. 1987a. Meteorological influences on harbour seal haul-out. Aquatic Mammals 13:114-118.

5. SEA WORLD EDUCATION DEPARTMENT (SWED). 1994. Harbor Seals. Sea World Education Department Publications, Bush Entertainment Corporation. San Diego, California. 359 pages.

6. TERHUNE, J.M. 1985. Scanning behavior of harbor seals on haul-out sites. Journal of Mammalogy 66:392-395.

7.  TOROK, M.L.  1994.  Movements, Activity Patterns, Dive Behavior, and Food Habits of Harbor Seals (Phoca vitulina richardsi) in San Francisco Bay, California.  88pp.

FOR MORE DETAILED INFORMATION VISIT http://www.seaworld.org/HarborSeal/hsintro.html

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