The Biogeography of the Harbor Seal (Phoca vitulina)

by Michelle Wilson,  student in Geography 316, Fall 2001

Taxonomic Classification: Kingdom: Animalia    Phylum: Chordata       Class: Mammalia          Order: Carnivora             Suborder: Pinnipedia                Family: Phocidae                   Subfamily: Phocinae                      Genus: Phoca                         Species: Phoca vitulina Subspecies: P.v. richardsi (Eastern Pacific Harbor Seal) P.v. concolor (Western Atlantic Harbor Seal) P.v. mellonae (Ungava Seal) P.v. stejnegeri (Western Pacific Harbor Seal) P.v. vitulina (Eastern Atlantic Harbor Seal)

Photo: Andrew Volkov, 2001

Description of Species:

Phoca vitulina, the scientific name for harbor seal, means “sea calf” or “sea dog.” These nicknames represent harbor seals well as these seals resemble a dog when their head pops up above the surface of the water. Harbor seals, also known as common seals or phoca, belong to the sub-order Pinnipedia, along with sea lions and walruses. Pinnipeds have adaptations that are key for their survival in cold, aquatic and environments. Swimming is made easier by their torpedo-shaped body the short paddle-like form of the limbs. They have a thick layer of blubber, which insulates the vital organs. Also, many pinniped species have the capability to slow their heart rate, increase flow of blood to vital functions, and tolerance of a high level of carbon dioxide, an adaptation that helps them dive depths over 1400 feet down and stay submerged for long periods of time (CAS 1977). Another adaptation harbor seals have are large eyes for good underwater vision. When they are underwater, a mucus membrane continually washes over the eyes in order to protect them. Harbor seals have spotted coats in shades ranging from silver-gray to black to dark brown. They are usually between 5 and 6 feet in length and weigh up to 300 pounds. Males are slightly larger than females. Their average life span can reach up to 25 years. They are true seals, meaning they have no external earflaps, and must move on land by flopping on their bellies. Harbor seals are gregarious creatures, tending to move in or form a group (Sanderson 1990). 
 
 

Natural History:
 
Habitat:

Harbor seals inhabit the coasts of the North Atlantic and North Pacific Ocean. These common seals live in small colonies of a few families in locations all along the coasts and especially where there are rocks. Harbor seals can also be found out on sand bars, remote beaches, mudflats, bays, and estuaries. These marine mammals spend their lives along the same stretch of coastline. Harbor seals can often be found in haul-out-sites, shoreline regions where seals congregate in order to molt, rest or nurse their pups. The ideal spot for any harbor seal is anywhere away from predators or humans with easy access to water and food.

Diet:
 
The diet of harbor seals depends on the region and the season. For the most part, they feed close to shore or in shallow waters. They feed on a variety of fish, cephalaopods, mollusks, and crustaceans. Herring, octopus, squid, shrimp, Pacific cod, capelin, eulachon, sculpin, and flatfishes are common prey of harbor seals. During high tides they tend to hunt for fish, crabs, and shellfish.

Mating/Reproduction:

Breeding season for harbor seals varies according to habitat and can be anytime from late winter to mid autumn. Harbor seals are sexually mature between the ages of three and seven and have reached a weight of about 165 pounds.  About six weeks after pups are born, mating season occurs. Harbor seals usually return to the same breeding grounds each year, and the mating process occurs in the water. Mating activities of harbor seals prior to the pupping season include rolling, bubble-blowing, and mouthing each other’s necks. After the pupping season, male harbor seals display mating behavior such as chasing, neck and flipper biting, and embracing. Female harbor seals respond to such behavior by growling, head-thrusting, and flipper-waving. The male harbor seals are polygynous, usually completing copulation with more than one female who come into estrus in his territory. Females don’t tend to mate with more than one male. (Renouf 1991). Delayed implantation occurs in harbor seals, when a fertilized egg is implanted but doesn’t begin to develop for two to three months, making gestation an approximate ten-month period. One single pup is born in the water or on land between the spring and mid summer months, and is weaned after 3-6 weeks.

Photo: Jessica Chong (AAST), 2001

Evolution:

The oldest known pinniped remains are from the Miocene period, about 35 million years ago  (Scheffer 1958). The pinnipeds evolved from arctoid, bearlike carnivorous ancestors that existed roughly 30 million years ago. Although there is controversy regarding whether seals belong to the order of Carnivora or Pinnipedia, most sources consider them to be members of Carnivora. Pinnipeds are so different from all living Carnivores that they are placed in a sub-order of their own: Pinnipedia.  The remaining sub-order of Carnivora is the terrestrial carnivore, Fissipedia (Giddleman 1989). The Carnivora are mammals of moderate to large size, with a primitive skeleton and a high ratio of brain-to-body weight. Several evolutionary lineages within the order Carnivora are now thought to have become either more or less aquatic (Anderson 1984). After the first mammal-like animal appeared on earth, several groups of land mammals began to live in the ocean in order to avoid land predators and to take advantage of the abundant food available in the marine environment. Seals were once one of these land-dwelling animals that moved into the sea about 20 million years ago. Pinnipeds have evolved into mammals that are able to live an aquatic and terrestrial life. Each family of pinniped has developed different features that help them adapt to a certain way of life. The early pinnipeds moved along the shores of continents, from island to island, and later to polar ice fields (Scheffer 1958). The Phocidae family body type and limbs are more specialized for pelagic life. Some of these adaptations that harbor seals have developed over time include: a torpedo shaped body for better swimming, internal ears, sex organs and mammary glands that retract into the body when not in use, flippers instead of hands and feet, flat hair in order to pass smoothly through the water, and a thick layer of blubber in order to minimize loss of heat. Like most phocids, harbor seals originated in the Northern Hemisphere. 

Source: Evolutionary Tree of Carnivores (Savage & Long 1986).

Distribution:

Harbor seals live in all parts of the Northern Hemisphere and are found in arctic, subarctic, and temperate waters. These true seals are environmentally adaptable to many environments, a fact that tells us why they have a wide distribution all over the world (Evans 1986). Harbor seals have a discontinuous distribution, meaning their distribution is widely scattered over the world. The subspecies of Phoca vitulina that inhabits the coasts of California is called Phoca vitulina richardsi. The Pacific Harbor Seal is distributed along the coasts from Alaska all the way down to Baja California. Harbor seals are not known to migrate regularly, but will travel in search of feeding ground.
 
 Distribution Map:

TABLE: Harbor seal populations and distributions
Source: (c)2001 SeaWorld Inc. Busch Entertainment Corp. All Rights Reserved.

Other interesting issues:
 
Predators:

Depending on the region where a harbor seal lives, they might be preyed upon the following animals:
killer whales, sharks, polar bears, Stellar sea lions, walruses, coyotes, and eagles.

Human Impact: 

Harbor seals are directly affected by marine pollution. Marine debris, debris that is not naturally part of a marine environment, is a threat to harbor seals. They can become entangled in fishing nets or plastic packaging materials, causing injury or drowning. Harbor seals can also ingest plastic materials, which can cause starvation and obstructions in the digestive tract. 

Conservation:
 
Harbor seals are protected by the U.S. Marine Mammal Protection Act (MMPA) of 1972. This act made it illegal to hunt any marine mammal in U.S waters. The only exceptions include the following: native subsistence hunting and collecting or temporarily keeping marine mammals for research, education, or public display. 

 
Bibliography: 
 Anderson, Sydney, ed. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons, 1984.

Chong, Jessica. (2001).  "Harbor Seals: Behavior" [Online]. Available:
    http://www.bergen.org/Smithsonian/HarborSeal/HSBehavior.htm [20 October 2001].

Evans, Phyllis R. The Sea World Book of Seals and Sea Lions. San Diego: Harcourt Brace Jovanovich, 1986.

FAO Advisory Committee on Marine Resources Research Working Party on Marine Mammals. Mammals in the Seas.
    Volume IV. Food and Agriculture Organization of the United Nations. Rome, 1982.

Garrison, Bob. (May/June 1994). "Watchable Wildlife: Harbor Seals." [Online]. Available:
     http://www.dfg.ca.gov/watchable/seals.html [15 October 2001].    

"Harbor Seals." Encarta Encyclopedia. CD-ROM, 2000.

Loomis, Jerry. (2001). "Marine Mammals." [Online]. Available: http://pt-lobos.parks.state.ca.us/nathis/MarineMam.htm

Marine Mammal Center. (2001). "Pacific Harbor Seal." [Online]. Available: http://www.tmmc.org/harborsl.htm
     [20 October 2001].

Renoult, Deane, ed. Behaviour of Pinnipeds. London: Chapman and Hall, 1991. 

Reynolds III, John E., and Sentiel A. Rommel, eds. Biology of Marine Mammals. Washington: Smithsonian Institution 
    Press, 1999.

San Francisco Bay Seal Project. (2001). "Harbor Seal: Phoca Vitulina." [Online]. Available: 
    http://earthisland.org/immp/seal.html [20 October 2001].

Sanderson, Ivan T. Living Mammals of the World. New York: Hanover House, 1990.

Savage, R. J. G., and M. R. Long. Mammal Evolution: An Illustrated Guide.  London: British Museum, 1986.

Scheffer, Victor B. Seals, Sea Lions, and Walruses: A Review of the Pinnipedia. Stanford: Stanford University Press, 
    1958.

Sea World. (2001). "Animal Information Database: Harbor Seals." [Online]. Available:
    http://www.seaworld.org/infobooks/HarborSeal/home.html [20 October 2001].

Seal Conservation Society: Harbor Seal. (2001). "Pinniped Species Information Pages: Harbor Seal." [Online].
    Available:  http://www.pinnipeds.fsnet.co.uk [16 October, 2001].

"Seal (mammal)," Microsoft Encarta Online Encyclopedia 2001. [Online]. Available:
    http://encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761564979 [1 November 2001].             

Volkov, Andrew. (1998). "California Harbor Seals" [Online]. Available: 
    http://animalpicturesarchive.com/animal/APAsrch3.cgi?qt=harbor+seals&type=image [15 October 2001].

send comments to bholzman@sfsu.edu
 

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