Harbor seal

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Harbor (common) seal
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Carnivora
Suborder:Pinnipedia
Family:Phocidae
Genus:Phoca
Species:P. vitulina
Binomial name
Phoca vitulina
Linnaeus, 1758 [2]
Subspecies

P. vitulina concolor (DeKay, 1842)
P. vitulina mellonae (Doutt, 1942)
P. vitulina richardsi (Gray, 1864)
P. vitulina stejnegeri (J. A. Allen, 1902)
P. vitulina vitulina Linnaeus, 1758

Range of Phoca vitulina
 
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Harbor (common) seal
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Carnivora
Suborder:Pinnipedia
Family:Phocidae
Genus:Phoca
Species:P. vitulina
Binomial name
Phoca vitulina
Linnaeus, 1758 [2]
Subspecies

P. vitulina concolor (DeKay, 1842)
P. vitulina mellonae (Doutt, 1942)
P. vitulina richardsi (Gray, 1864)
P. vitulina stejnegeri (J. A. Allen, 1902)
P. vitulina vitulina Linnaeus, 1758

Range of Phoca vitulina

The harbor (or harbour) seal (Phoca vitulina), also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere. The most widely distributed of pinniped (walruses, eared seals, and true seals), they are found in coastal waters of the northern Atlantic and Pacific oceans, the Baltic and North Seas.

Harbor seals are brown, tan, or gray, with distinctive V-shaped nostrils. An adult can attain a length of 1.85 meters (6.1 ft) and a mass of 132 kilograms (290 lb). Females outlive males (30–35 years versus 20–25 years). Harbor seals stick to familiar resting spots or haulout sites, generally rocky areas (although ice, sand and mud may also be used) where they are protected from adverse weather conditions and predation, near a foraging area. Males may fight over mates underwater and on land. Females bear a single pup, which they care for alone. Pups are able to swim and dive within hours of birth, developing quickly on their mothers' fat-rich milk. Blubber under their skins helps to maintain body temperature.

Their global population is 5–6 million, but subspecies in certain habitats are threatened. Once a common practice, sealing is now illegal in many nations within the animal's range.

Contents

Description

A young harbor seal on the coast of La Jolla, San Diego

Individual harbor seals possess a unique pattern of spots, either dark on a light background or light on a dark. They vary in color from brownish black to tan or grey; underparts are generally lighter. The body and flippers are short, heads are rounded. Nostrils appear distinctively V-shaped. As with other true seals, there is no pinna (ear flap). An ear canal may be visible behind the eye. Including the head and flippers, they may reach an adult length of 1.85 meters (6.1 ft) and a weight of 55 to 168 kg (120 to 370 lb).[3] Females are generally smaller than males.

Population

There are an estimated 5 million to 6 million harbor seals worldwide. While the population is not threatened as a whole, the Greenland, Hokkaidō and Baltic Sea populations are exceptions. Local populations have been reduced or eliminated through disease (especially the phocine distemper virus) and conflict with humans, both unintentionally and intentionally. It is legal to kill seals perceived to threaten fisheries in the United Kingdom, Norway and Canada, but commercial hunting is illegal. Seals are also taken in subsistence hunting and accidentally as bycatch (mainly in bottomset nets). Along the Norwegian coast bycatch accounted for 48% of pup mortality.[4]

Seals in the United Kingdom are protected by the 1970 Conservation of Seals Act, which prohibits most forms of killing. In the United States the Marine Mammal Protection Act of 1972 prohibits the killing of any marine mammals. On the East Coast of the US their numbers are increasing steadily as they are reclaiming parts of their range, and have been seen as far south as Florida.

Subspecies

There are five subspecies of Phoca vitulina:

Habitat and diet

Skeleton

Harbor seals prefer to frequent familiar resting sites. They may spend several days at sea and travel up to 50 kilometers in search of feeding grounds, and will also swim some distance upstream into freshwater in large rivers. Resting sites may be both rugged, rocky coasts, such as those of the Hebrides or the shorelines of New England, or sandy beaches.[1] Harbor seals frequently congregate in harbors, sandy intertidal zones,[1] and estuaries in pursuit of prey fish such as menhaden, anchovy, sea bass, herring, mackerel, cod, whiting and flatfish, and occasionally shrimp, crabs, mollusks and squid. Although primarily coastal, dives to over 500 m have been recorded.[6] Harbor seals have been recorded to attack, kill and eat several kinds of seabirds.[7]

Behavior and reproduction

A harbor seal colony in Helgoland, Germany

Harbor seals are gregarious animals, though they do not form groups as large as some other seals. When not actively feeding they will haul to rest. They tend to be coastal, not venturing more than 20 kilometers offshore. Both courtship and mating occur underwater. The mating system is not known, but thought to be polygamous. Females give birth once per year, with a gestation period of approximately nine months.

Birthing of pups occurs annually on shore. The timing of the pupping season varies with location,[8] occurring in February for populations in lower latitudes, and as late as July in the subarctic zone. The mothers are the sole providers of care, with lactation lasting four to six weeks. Researchers have found males gather underwater, turn on their backs, put their heads together and vocalize to attract females ready for breeding.[9] The single pups are born well developed, capable of swimming and diving within hours. Suckling for three to four weeks, pups feed on the mother's rich, fatty milk and grow rapidly; born weighing up to 16 kilograms, the pups may double their weight by the time of weaning.

Harbor seals must spend a great deal of time on shore when moulting, which occurs shortly after breeding. This onshore time is important to the life cycle, and can be disturbed when there is substantial human presence.[10] The timing of onset of moult depends on the age and sex of the animal, with yearlings moulting first and adult males last.[11] A female will mate again immediately following the weaning of her pup. Harbor seals are sometimes reluctant to haul out in the presence of humans, so shoreline development and access must be carefully studied in known locations of seal haul out.[citation needed]

Harbor seals in California

A pup nursing at Point Lobos

The California population of subspecies richardsi amounted to approximately 25,000 individuals as of 1984. Pacific harbor seals or Californian harbor seals are found along the entire Pacific coast shoreline of the state. They prefer to remain relatively close to shore in subtidal and intertidal zones, and have not been seen beyond the Channel Islands as a pelagic form; moreover, they will often venture into bays and estuaries and even swim up coastal rivers. They feed in shallow littoral waters on herring, flounder, hake, anchovy, codfish and sculpin.[12]

Breeding occurs in California from March to May, pupping between April and May, depending on local populations. As top level feeders in the kelp forest, harbor seals enhance species diversity and productivity. They are preyed upon by killer whales (orcas) and white sharks.

Considerable scientific inquiry has been carried out by The Marine Mammal Center and other research organizations beginning in the 1980s regarding the incidence and transmission of diseases in harbor seals in the wild, including analysis of phocine herpesvirus.[13] In the San Francisco Bay, some harbor seals are fully or partially reddish in color, possibly caused by an accumulation of trace elements such as iron or selenium in the ocean, or a change in the hair follicles.

See also

References

  1. ^ a b c Thompson, D. & Härkönen, T. (2008). Phoca vitulina. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 29 January 2009.
  2. ^ Linnæus, Carl (1758) (in Latin). Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I (10 ed.). Holmiæ (Stockholm): Laurentius Salvius. p. 38. http://www.biodiversitylibrary.org/item/80764#page/48/mode/1up. Retrieved 23 November 2012.
  3. ^ Kindersley, Dorling (2001,2005). Animal. New York City: DK Publishing. ISBN 0-7894-7764-5.
  4. ^ Bjørge, A.; Øien, N., Hartvedt, S.,Bøthum, G. and Bekkby, T. (2002). "Dispersal and bycatch mortality in grey, Halichoerus grypys, and harbour, Phoca vitulina, seals tagged at the Norwegian coast.". Mar. Mamm. Sci. 18: 963–976.
  5. ^ Berta, A. & Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies". Mammal Review 42 (3): 207–234. doi:10.1111/j.1365-2907.2011.00193.x.
  6. ^ Burns, J. J. 2002. Harbor seal and spotted seal Phoca vitulina and P. largha. In: W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 552–560. Academic Press.
  7. ^ "Harbour seal kills and eats duck", Tetrapod Zoology, 6 march 2008
  8. ^ Temte, J. L. 1994. "Photoperiod control of birth timing in harbour seal (Phoca vitulina)". Journal of Zoology (London) 233: 369–384.
  9. ^ Van Parijs, S. M. and Kovacs, K. M. 2002. "In-air and underwater vocalizations of eastern Canadian harbour seals, Phoca vitulina". Canadian Journal of Zoology 80: 1173–1179.
  10. ^ Patrick Sullivan, Gary Deghi and C.Michael Hogan, Harbor Seal Study for Strawberry Spit, Marin County, California, Earth Metrics file reference 10323, BCDC and County of Marin, January 23, 1989.
  11. ^ Reder, S., Lydersen, C., Arnold, W. and Kovacs, K. M. 2003. "Haulout behaviour of High Arctic harbour seals (Phoca vitulina vitulina) in Svalbard, Norway". Polar Biology 27: 6–16.
  12. ^ T.C. Newby, Pacific Harbor Seal, pp 184–191 in D. Haley, ed. Marine Mammals of Eastern North Pacific and Arctic Waters, Pacific Search Press, Seattle WA (1978)
  13. ^ Goldstein, T., Mazet, J.A.K., Gulland, F.M.D., Rowles, T., Harvey, J.T., Allen, S.G., King, D.P., Aldridge, B.M., Stott, J.L., "The transmission of phocine herpesvirus-1 in rehabilitating and free-ranging Pacific harbor seals (Phoca vitulina) in California", Veterinary Microbiology 103:131–141 (2004)

External links