Harbor Seal

Phoca vitulina

Summary 3

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.

Pacific Coast 4

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.

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. 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.

Although some of the largest pupping areas harbor seals are found in California, harbor seals are found north along the Pacific Coast of the US in both Oregon and Washington. Large populations move with the season down the West Coast of Canada and may winter on the islands in Washington and Oregon.

Behavior and reproduction 4

Harbor seals are solitary but are gregarious when hauled out and during the breeding season, 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, 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. 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. The timing of onset of moult depends on the age and sex of the animal, with yearlings moulting first and adult males last. 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.

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.

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. 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.

Although some of the largest pupping areas harbor seals are found in California, harbor seals are found north along the Pacific Coast of the US in both Oregon and Washington. Large populations move with the season down the West Coast of Canada and may winter on the islands in Washington and Oregon.

Harbor seals are normally found along the Atlantic Coast and islands from Maine southward to Massachusetts. Occasionally, areas further south in Connecticut, Long Island, New Jersey, and even North Carolina have reported small populations or stranded seals have been found in and near islands or on beaches. Harbor seals move down from eastern Canadian waters to breed along the coast of Maine in May and June, and return northward in fall. Massachusetts is the southernmost point of known pupping areas along the Atlantic Coast.

Behavior and reproduction 4

Harbor seals are solitary but are gregarious when hauled out and during the breeding season, 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, 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. 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. The timing of onset of moult depends on the age and sex of the animal, with yearlings moulting first and adult males last. 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.

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.

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. 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.

Although some of the largest pupping areas harbor seals are found in California, harbor seals are found north along the Pacific Coast of the US in both Oregon and Washington. Large populations move with the season down the West Coast of Canada and may winter on the islands in Washington and Oregon.

Harbor seals are normally found along the Atlantic Coast and islands from Maine southward to Massachusetts. Occasionally, areas further south in Connecticut, Long Island, New Jersey, and even North Carolina have reported small populations or stranded seals have been found in and near islands or on beaches. Harbor seals move down from eastern Canadian waters to breed along the coast of Maine in May and June, and return northward in fall. Massachusetts is the southernmost point of known pupping areas along the Atlantic Coast.

Habitat and diet 4

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. Harbor seals frequently congregate in harbors, sandy intertidal zones, 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. Atlantic subspecies of either Europe or North America will also exploit deeper dwelling fish of the genus Ammodytes as a food source and Pacific subspecies have been recorded occasionally consuming fish of the genus Oncorhynchus. Although primarily coastal, dives to over 500 m have been recorded. Harbor seals have been recorded to attack, kill and eat several kinds of duck.

Habitat and diet 4

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. Harbor seals frequently congregate in harbors, sandy intertidal zones, 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. Atlantic subspecies of either Europe or North America will also exploit deeper dwelling fish of the genus Ammodytes as a food source and Pacific subspecies have been recorded occasionally consuming fish of the genus Oncorhynchus. Although primarily coastal, dives to over 500 m have been recorded. Harbor seals have been recorded to attack, kill and eat several kinds of duck.

Sources and Credits

  1. (c) California State Parks, all rights reserved, uploaded by Mike Merritt, http://www.inaturalist.org/photos/3808625
  2. (c) David A. Hofmann, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/23326361@N04/3062183829/
  3. Adapted by Mike Merritt from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Phoca_vitulina
  4. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Harbor_seal

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