Harbor seal

Phoca vitulina




Phoca vitulina Linnaeus, 1758, "in mari Europaeligo." OTHER COMMON NAMES

English: Common seal, kuril seal, island seal, spotted seal. PHYSICAL CHARACTERISTICS

Males: 5.3-6.3 ft (1.6-1.9 m); 194-312 lb (88-142 kg); Females: 4.9-5.6 ft (1.5-1.7 m); 143-235 lb (65-107 kg). There is considerable variation in pelage coloration both within and among the five subspecies of this species; there is no difference between the sexes. The Atlantic subspecies have background color of various shades of gray or cream covered with dark spots. The Pacific subspecies have light and dark variants of coat color. The dark pelage consists of dense black spots, some of which are outlined by a silver ring. The light pelage has a darker upper body but the sides and underbody have a silvery background with dark spots. Most pups are born without a white natal coat, which has been shed in utero. Consequently, they look like miniature adults.


These seals are found broadly in the Northern Hemisphere in coastal areas of both the east and west Atlantic Ocean and of the east and west Pacific Ocean.


Breed, rest and molt on sand and cobble beaches, rocky islets, sand bars and occasionally ice floes. They may forage in estuaries, along the continental shelf or in deeper waters off the shelf. One population is found in an inland lake.


During the breeding season, males and females with pups form small mixed groups on land in areas traditionally used for pupping. There is no clear organizational structure to these groups. Males spend less time on land at this time than do females with pups. Several weeks after breeding, both sexes haul out to molt. Molting groups may be much larger than the size of groups during breeding. During intensive foraging between breeding and molting, seals disperse to forage rather than migrate to specific forage areas. Harbor seals engage in little in-air vocalizations, but during the mating period males appear to use underwater displays that have visual and vocal components. Females of this species make foraging trips during lactation, similar to those seen in otariid seals.


Foraging patterns and diets of this species are highly variable and depend on local environments. Around Sable Island in Atlantic Canada, foraging is typically at depths of 66-165 ft (20-50 m), whereas in areas of the Pacific it is not uncommon for foraging depths to exceed 330 ft (150 m). The primary food for this species is small to medium size fishes followed by cephalopods (such as squid and octopus). While there may be many species identified as prey items for a given population,

H Phoca vitulina H Leptonycotes weddellii there is usually a couple of species that predominate and this may vary seasonally and inter-annually. At Sable Island, sand eels (Ammodytes spp.) predominate. Around the Aleutian Islands in the Pacific, Atka mackerel (Pleurogrammus monopterygius) is the main fish eaten. On another level, diets in the Moray Firth of Scotland showed Atlantic cod (Gadus morhua) as the main food in January, whereas in June cod was the dominant prey. In January two years later herring (Clupea harengus) was the major food.


Mating in this species occurs at sea so it has been difficult to study the mating system. Recent studies using dive recorders, video cameras, hydrophones, and DNA analyses have begun to reveal some information. Males appear to be polygynous, but at a fairly low level (maximum success of fertilizing five females). In some locations, males may defend territories to control access to females and in others males may display (blowing bubbles and vocalizing) from aquatic positions to attract females. Much more research is needed to confirm such patterns. Males produce sperm about three to seven years of age but do not become successful breeders until older, probably at least 10 years of age. Females give birth for the first time from three to seven years of age, and give birth to a single young annually. Lactation is about 24 days and females produce milk averaging 50% fat. As noted above, females do not fast entirely during lactation and begin regular foraging trips to supplement blubber stores to fuel the production of milk during lactation.


This species is not threatened, but several major die-offs have occurred in recent years with thousands of seals dying from diseases not previously known to be a problem. The coastal nature of this species makes them particularly vulnerable to human-induced impacts such as pollution.


There are small amounts of subsistence hunting of these seals for food and hides, but the species is of no major significance to humans. ♦

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