~ Harp & Harbor Seals ~
Adult male harp seals grow to about 1.7 m and 130 kg; females are slightly smaller. Gregarious by nature, harp seals haul out in dense herds to give birth and moult. Females and males reach sexual maturity at approximately 4-6 years of age. A single pup weighing about 10 kg (22 lbs) is born each year from mid February to March. Mating occurs after the pups are weaned at about 12 days. After mating, adult males are joined on the moulting patches by immature and non-breeding seals, followed by adult females. Harp seals consume a wide range of prey species and their diet appears to vary with age, season, location and year. Harp seals can live up to 30 years.
Distribution and Habitat:
Harp seals inhabit the North Atlantic and Arctic Oceans from northern Russia, to Newfoundland and the Gulf of St. Lawrence, Canada. They are separated into three populations based on where they breed... the White Sea, the "West Ice" and the Northwest Atlantic "Gulf" and "Front". Harp seals are closely associated with pack ice, undergoing spring migrations of up to 2,500 km on their way to summer feeding grounds, returning south ahead of the new ice in the fall.
All three populations exhibit similar patterns of annual migration, although the timing of specific events such as pupping, varies slightly from place to place.
The Northwest Atlantic harp seal population is the largest and most studied. The best estimate of 1994 population size is 4.5 million animals. The population is now showing signs of reaching the limit of its food base and may be declining as a result of increased sealing since 1996. In 1994 pup production and population size for the West Ice were estimated at 59,000 and 286,000, respectively. A 1998 survey in the White Sea found that pup production was on the order of 300,000 - 400,000, higher than previously thought. These results are consistent with a total population size of about 1.5 to 2.0 million animals.
Threats to the Species:
All three populations are hunted annually. Harp seal pups are easily taken because they have no fear of man, hunters can simply walk up to a pup and club it to death. Seal pups are clubbed in the head rather than shot or speared to keep their coats from being damaged. Over-exploitation, particularly in the Northwest Atlantic, and an expanding and unregulated trade in seal products remain a threat. Other potential threats include: proposals to cull harp seal populations, ostensibly to benefit fisheries, reduced food availablilty due to human overfishing or climate change, incidental catches in fishing gear, and environmental contaminants.
Distribution and Population:
The harbor seal is the most widely-distributed pinniped, inhabiting temperate and subarctic coastal areas on both sides of the north Atlantic and north Pacific Oceans. Population estimates are imprecise or unavailable for most areas in the harbor seal's range. It is thought however that there may be a total world population of about 400,000-500,000 seals. There has been much debate in recent years regarding the classification of the species, but five separate subspecies are generally recognised at the present time.
These five subspecies include:
1. Eastern Atlantic harbor seal also known as the common seal.
2. Western Atlantic harbor seal.
3. Eastern Pacific harbor seal.
4. Western Pacific harbor seal.
5. Ungava Seal.
There is much variation in the appearance, physiology and behaviour of the harbor seal throughout its wide range. Generally, however, the species is gregarious, hauling out in small scattered groups to breed, moult and rest. Many different types of habitat are used for hauling out, including rocky shores, reefs, skerries, sand and gravel beaches, intertidal mud and sand bars, piers, and, in some places, drifting glacial ice. In general the species seems to prefer protected rather than exposed areas. Suitable characteristics for a haulout site seem to include adequate protection from land predators, direct access to deep water, proximity to food resources, and protection from strong wind and waves. It is thought that the necessity to avoid predators is one of the main reasons that harbor seals prefer to haul out in groups rather than alone. The species' haulout patterns tend to be strongly influenced by tidal cycles and many seals haul out on the falling tide in areas below the high tide mark. Lesser numbers of harbor seals are generally seen hauled out in autumn and winter than in spring and summer. Individuals of the species tend to stay in the same area all year round. Some seals, particularly juveniles, are however known to travel long distances, sometimes up to 500km, to feed. More localised movements in search of food, or perhaps to follow migrating fish, are common. Harbor seals tend to stay within 20km of the shore but individuals are occasionally found 100km or more offshore. Some seals seasonally visit or inhabit freshwater streams and lakes, while the distribution range of many populations seems to be extended during the autumn.
Pupping seasons vary for different populations. Most pups are born with their adult coat, having shed a grey-white woolly coat before birth. Some pups however, especially the pups of younger mothers, are born with this pre-natal coat and moult it shortly afterwards. Harbor seal pups are precocious and are almost immediately able to crawl and swim, often within an hour of birth. This adaptation is essential for those pups born in intertidal areas. Pups weigh an average of 13-14% of their mother's body weight at birth, large compared to other phocid seals at 8-10%. Nursing of the pup, mostly on land but also in water, usually takes about 4 weeks. The pup puts on weight at the rate of around 0.5-0.7kg per day. During this time the mother makes short feeding trips, the duration of which become longer through the nursing period. Weaning of the pup can either be abrupt or gradual, both mother and pup becoming less interested in each other towards the end of the nursing period. After being weaned the pups tend to disperse from their birth site, often travelling long distances to explore their new habitat. The vast majority of the lakes and rivers in the subspecies' range are covered by ice at the time of pupping. It is thought that the seals may winter in the larger lakes and then disperse into the smaller rivers and lakes when the ice melts.
Coat Patterns and Moulting:
The pattern of harbor seal coats varies widely. The background colour, often brown, tan or grey, ranges from dark to light in different seals and is covered with light or dark rings, spots and blotches. The pattern on a harbor seal's coat is unique to each seal and does not change from year to year, a useful feature in the identification of individuals. A red to orange coloration is also found in a number of seals, especially in San Francisco Bay which has the highest incidence of red fur in the world, 40% of the seals on average compared to 1% at most other locations. The time of year and duration of the moult vary between populations, also varying within each population for individuals of differing age, sex and reproductive status. Seals haul out a lot during the moult, probably because warm skin enhances the growth of new hair. The metabolism of harbor seals also reduces while they are moulting, meaning that the seals do not need to spend as much time catching food during the moult than at other times of the year.
Pupping and Moulting Seasons:
- Eastern Atlantic: Pupping: June to mid-July. Moulting: June - September.
- Western Atlantic: Pupping: mid-May to July. Moulting: July - August.
- Eastern Pacific: Pupping: February-March in Mexico and progressively later northwards up to British Columbia and Washington (June - September). May-July in Alaska. Moulting: May - October, taking place progressively later the further north the population goes.
- Western Pacific: Pupping: mid-May to July.
- Ungava Seal: Pupping: mid-April to mid-May.
Mating takes place around the time of weaning and, for the most part, in the water. Very little is known about the mating habits of harbor seals, although recent studies indicate that the adult males gather in an area where females may be attracted to mate. During this period the males perform aquatic displays and underwater vocalisations that may be related to competition with other males or may serve to attract females. Many fights between males take place and neck wounds are commonly seen during this period. Males lose up to 25% of their body weight during the breeding season from the energetic requirements of competing and breeding.
Feeding Habits and Predators:
Harbor seals are opportunistic foragers, feeding on locally and seasonally abundant prey that includes a large number of species of fish, crustaceans and molluscs. Feeding is usually carried out near the shore, individuals diving to fairly shallow depths, usually less than 100m, for short periods of a few minutes. Most feeding trips last less than 12 hours. Ungava seals haul out in small groups in spring but alone or in pairs at the end of summer. The subspecies feeds exclusively in freshwater and is the only known harbour seal population resident in freshwater all year round. The diet of Ungava seals has not been well studied, but they are known to prey on salmonids such as small brook trout. The harbor seal species are preyed upon in many parts of its range by killer whales and sharks. Polar bears are known to be predators of Western Atlantic harbour seals. Pups may also be preyed on by foxes and large birds of prey, while harbor seals in the Pacific are known to be killed by Steller sea lions.
Alaskan and western Pacific harbor seals are significantly larger than those in the Atlantic and those in the more southern areas of the eastern Pacific. Hokkaido seals appear to be the largest with an average length of 1.9m for adult males and 1.7m for adult females. Generally however adult males measure 1.4-1.9m in length and weigh 55-170kg, while the smaller adult females measure 1.2-1.7m in length and weigh 45-105kg. Pups are usually born measuring 70-100cm in length and weighing 8-12kg. Females reach sexual maturity at 3-6 years, males at 3-7 years. Harbor seals have sometimes been known to dive over 500m and for periods over 25 minutes. Male harbor seals have a shorter lifespan than females, possibly due to the stress of competing and fighting during the breeding season, males living up to 20-25 years and females living up to 30-35 years.
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