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harbor seal

Phoca vitulina

What do they look like?

The bodies of harbor seals are specialized for diving and living in cold water. They have big round heads and long, flat flippers made of five webbed digits. They don't have ears on the outside of their heads but have large middle ear bones. They conserve oxygen while diving for food by slowing down their heart rate and not breathing underwater. Their back limbs and flexible upper bodies make them quick and mobile in the water. They have thick layers of fat under the skin which give them energy and keep them warm. This also makes the speed they use food energy 1.7 to 2.2 times higher than land mammals that are the same size. They are covered in fur that protects their skin from damage while they are on land. They can have either a yellowish coast with small black ringed spots, or a black coat with dark spots that have light rings on their back. Adult male harbor seals are larger than females. Males are 160 to 190 cm long and weigh 80 to 170 kg. Females are 160 to 170 cm long and weigh 60 to 145 kg. (Berta, et al., 2006; Burns, 2008; Nowak, 2003; Riedman, 1990)

  • Sexual Dimorphism
  • male larger
  • Average mass
    80 to 170 kg
    lb
  • Average mass
    115000 g
    4052.86 oz
    AnAge
  • Average length
    160 to 190 cm
    in
  • Average basal metabolic rate
    73.29 W
    AnAge

Where do they live?

Harbor seals live in a larger area than any other kind of seal, sea lion, or walrus. They are native to the east and west coasts of the Pacific and Atlantic Oceans in the Northern Hemisphere. They live along the western Pacific Ocean coast north to the Gulf of Alaska and to the southeastern Bering Sea. In the western Atlantic ocean, they live along the French coast, up to the North Sea and the Barents Sea, as well as along the east coast of the United States and Canada. There are five subspecies, but scientists are not exactly sure where one subspecies ends and another begins. (Boness, 2004; Burns, 2008; Riedman, 1990)

What kind of habitat do they need?

Harbor seals live in shallow water along the coast, in protected bays, islands along the coasts, and where the ocean meets large rivers. They are commonly spotted on beaches and near piers. They are more common in colder ocean waters that aren't frozen year-round. They usually hunt at ocean depths of 91 m, but can dive as deep as 427 m. (Boness, 2004; Burde and Feldhamer, 2005; Burns, 2008; Riedman, 1990; Spies, 2007)

  • Range depth
    427 (high) m
    1400.92 (high) ft
  • Average depth
    91 m
    298.56 ft

How do they reproduce?

Harbor seals males try to attract females in a few different ways. They show off by making noises, performing deep dives, or by competing against other males. They get in fights when they are on shore and when there are a lot of females around. Scientists don't know very much about their mating habits. Usually males breed with just one female, but sometimes with more than one. (Boness, 2004; Burns, 2008; Nowak, 2003)

Female harbor seals usually give birth to one pup every season. About 85% of females are pregnant in the same year. They are able to have twins as well. The baby grows inside the mother for about ten and a half months. Harbor seals are born near the shore or on land, probably because there are not as many predators. (Burns, 2008; Coltman, et al., 1998; Nowak, 2003)

Nearly all harbor seal pups are born in late winter to summer. They weigh 8 to 12 kg as newborns. When they are born, their fur is like adult fur, which keeps them warm in cold water. They don't develop a full coat until the end of their first summer. After 4 to 6 weeks, pups are able to eat more than just their mother's milk. Female harbor seals can have their own pups after 3 to 4 years, and reach full size after 6 to 7 years. Male harbor seals can have their own pups after 4 to 5 years and reach full size after 7 to 9 years of age. (Burns, 2008; Coltman, et al., 1998; Nowak, 2003)

  • How often does reproduction occur?
    Harbor seals usually breed once per year, normally in late winter to summer.
  • Breeding season
    Breeding occurs during a 10 week period.
  • Range number of offspring
    0 to 2
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    10.5 months
  • Average gestation period
    253 days
    AnAge
  • Range weaning age
    4 to 6 weeks
  • Range time to independence
    4 to 6 weeks
  • Average age at sexual or reproductive maturity (female)
    3-4 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    1095 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    4-5 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    1460 days
    AnAge

Female harbor seals use more effort caring for newborn pups than males do. Mothers bond with with their pups in the first hour after they are born. Mothers nurse their pups with milk for about 4 to 6 weeks. The milk is made up of about 50% fat, so the pups grow quickly. While they are only drinking milk, they cling to their mother’s backs while traveling through the water. (Allen, et al., 1988; Burde and Feldhamer, 2005; Burns, 2008; Geraci and Lounsbury, 2005; Nowak, 2003)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

How long do they live?

In the wild, harbor seals live about 40 years. The longest recorded lifespan in captivity is 47.6 years. (de Magalhaes and Costa, 2009)

How do they behave?

Harbor seals are active during the day and are usually found by themselves. Right after they have pups or when they are shedding their fur, they can be found in groups of males, females, and pups. These groups don't have social organization or hierarchies. Harbor seals spread out to search for food instead of traveling together to a special feeding location. (Boness, 2004)

Harbor seals often move from the ocean waters onto land or icebergs. This makes it easier for them to give birth, maintain their body temperature, rest, and stay away from predators. They often move onto land when they shed all their fur, which happens 2 to 3 months after they have pups. Usually pups shed their fur first, then juveniles, then female adults, and lastly male adults. Whether they move to land or not also always depends on the weather. (Boness, 2004; Burns, 2008)

Harbor seals can dive to depths of 427 m and stay underwater for almost 30 minutes without coming up for air. They usually don't dive this far down, though. Their average dive lasts a few minutes and is 91 m deep. They dive in V-shapes or U-shapes for catching prey. (Baechler, et al., 2002)

  • Average territory size
    25 m^2

Home Range

Harbor seals usually stay within 50 meters of the spot where they got out of the water, and spend most of their time even closer (within 10 meters). Staying close to land keeps them away from predators. (Grigg, et al., 2009; Nowak, 2003)

How do they communicate with each other?

Harbor seals seem to always be aware of their surroundings, even when they are in captivity. They make fewer noises than other seals, which may help them avoid predators. The sounds they make have frequencies of 0.1 to 10 kHz. They make noises that sound like burping, grunting, and yelping. Harbor seals are playful animals and often play by themselves or with seaweed or other objects. They have large eyes that are specialized to take in more light to see brighter images in dark water. They have sensitive whiskers that pick up sound waves, helping them catch prey. Harbor seals often slap their flippers on the water, but scientists don't know exactly why. (Burns, 2008; Nowak, 2003; Riedman, 1990)

What do they eat?

Harbor seals are carnivores that eat mostly fish. They eat fish that are easy to catch so that they don't have to spend as much energy hunting. Adult harbor seals eat fish whole or head-first. They prefer to eat codfish, hake, mackerel, and herring. Other times, they eat octopus, squid, and also crustaceans like crabs and shrimp. Young harbor seal pups are not very good at diving, so they eat more crustaceans that are easier to catch. Adult harbor seals that weigh 100 kg eat around 5 to 7 kg of food per day. (Berta, et al., 2006; Burns, 2008; Grigg, et al., 2009; Nowak, 2003)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

What eats them and how do they avoid being eaten?

Predators of harbor seals are sharks, killer whales, and polar bears. They are safer when they are land, but there is still danger. For example, coyotes sometimes prey on pups when their mothers are out looking for food. Humans also hunt them in some parts of the Arctic. (Geraci and Lounsbury, 2005; Nowak, 2003; Riedman, 1990)

What roles do they have in the ecosystem?

Harbor seals can have many parasites. These include roundworms called Pseudoterranova decipiens and Contracaecum osculatum and tapeworms called Anophryocephalus and Diplogonoporus. Most of the parasites that live on their skin are harmless. However, if they get infected while they are already sick, they can die. Parasites can also transmit bacteria or viruses and make them sick. The bacteria that kills most harbor seals and related animals is called Leptospira interrogans. (Geraci and Lounsbury, 2005; Herreman, et al., 2011)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • nematodes (Pseudoterranova decipiens)
  • nematodes (Contracaecum osculatum)
  • cestodes (Anophryocephalus)
  • cestodes (Diplogonoporus)
  • bacteria (Leptospira interrogans)

Do they cause problems?

Harbor seals have a negative impact on fishermen because they eat a lot of fish and get tangled in nets that could have been used to catch fish. (Jefferson, et al., 2008)

How do they interact with us?

Harbor seals are hunted for their meat, fur, skin, and fat tissue which is burned for energy. They may also generate economic value from ecotourism. (Riedman, 1990)

  • Ways that people benefit from these animals:
  • food
  • body parts are source of valuable material
  • ecotourism
  • research and education

Are they endangered?

The number of harbor seals worldwide has been increasing since around the 1970s. However, many harbor seals have died in recent years from new diseases. They are also at risk for damage from pollution, because they live along the coast. On the IUCN Red List, they are listed as "least concern." On the other hand, two harbor seal subspecies are currently on the brink of extinction. The number of Japanese harbor seals, called Phoca vitulina stejnegeri, has decreased since the 1980s because of overhunting. Another species called Phoca vitulina mellonae that lives in the Ungava Peninsula in Canada now includes only 120 to 600 seals. They are at high risk because they have low genetic variation and have been affected by installing river dams. No serious efforts to conserve these subspecies are currently occuring.

Contributors

Kristan Cale (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Catherine Kent (editor), Special Projects.

References

Allen, S., C. Ribic, J. Kjelmyr. 1988. Herd segregation in harbor seals at Point Reyes, California. Calif. Fish and Game, 74/1: 55-59.

Baechler, J., C. Beck, W. Bowen. 2002. Dive shapes reveal temporal changes in the foraging behaviour of different age and sex classes of harbour seals (Phoca vitulina). Canadian Journal Of Zoology, 80/9: 1569.

Berta, A., J. Sumich, K. Kovacs. 2006. Marine Mammals: Evolutionary Biology. Burlington, MA: American Press.

Boness, D. 2004. True Seals (Phocidae): Harbor Seal. Pp. 417-436 in M Hutchins, A Evans, J Jackson, D Kleiman, J Murphy, D Thoney, eds. Grzimek's Animal Life Encyclopedia, Vol. 14: Mammals III, 2nd Edition. Detroit: Gale.

Burde, J., G. Feldhamer. 2005. Mammals of the National Parks. Baltimore, MD: The Johns Hopkins University Press.

Burns, J. 2008. Encyclopedia of Marine Mammals. Pp. 533-541 in W Perrin, B Wursig, J Thewissen, eds. Harbor Seal and Spotted Seal, Vol. 1, 2 Edition. New York, NY: Academic Press.

Coltman, D., W. Bowen, J. Wright. 1998. Male mating success in an aquatically mating pinniped, the harbour seal (Phoca vitulina), assessed by microsatellite DNA marker. Behavioral Ecology and Sociobiology, 7/5: 627-638.

Geraci, J., V. Lounsbury. 2005. Marine Mammals Ashore: A Field Guide for Strandings. Baltimore, MD: National Aquarium in Baltimore.

Grigg, E., A. Klimley, S. Allen, D. Green, D. Elliott-Fisk, H. Markowitz. 2009. Spatial and seasonal relationships between Pacific harbor seals (Phoca vitulina richardii) and their prey, at multiple scales. Fishery Bulletin, 107/3: 359-372.

Herreman, J., A. McIntosh, R. Dziuba, G. Blundell, M. Ben-David, E. Greiner. 2011. Parasites of harbor seals (Phoca vitulina) in Glacier Bay and Prince William Sound, Alaska. Marine Mammal Science, 27/1: 247-253.

Jefferson, T., M. Webber, R. Pitman. 2008. Marine mammals of the World. Canada: Elsevier.

Nowak, R. 2003. Walker's Marine Mammals of the World. Baltimore, MD: The John Hopkins University Press.

Riedman, M. 1990. The Pinnipeds: Seals, Sea Lions, and Walruses. Oxford, England: University of California Press.

Spies, R. 2007. Long-Term Ecological Change in the Northern Gulf of Alaska. Kidlington, Ox, UK: Elsevier B.V..

de Magalhaes, J., J. Costa. 2009. A database of vertebrate longevity records and their relation to other life-history traits. Journal of Evolutionary Biology, 22/8: 1770-1774.

 
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Cale, K. 2012. "Phoca vitulina" (On-line), Animal Diversity Web. Accessed November 25, 2014 at http://www.biokids.umich.edu/accounts/Phoca_vitulina/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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