Seals
Harbor Seals
General
Description and Status
Harbor seals, Phoca vitulina concolor, are the most abundant
pinniped species off the eastern coast of the United States. Their maximum
length is nearly 6 feet. Harbor seals are recognized by their short,
concave snout, giving them a profile shaped much like the head of a
dog. Approximately 4,000-4,500 harbor seals are believed to overwinter
in southern New England (Payne and Selzer 1989).
Distribution
and Abundance
Harbor seals range from Labrador to Long Island, New York with occasional
sightings as far south as South Carolina and Florida (Brimley 1931,
Caldwell and Caldwell 1969, Payne and Selzer 1986). This species previously
bred as far south as Cape Cod during the first part of the twentieth
century (Katona et al. 1993). However, their breeding range and seasonal
distribution have changed over time which has most likely been a direct
result of a state-offered bounty in effect in Massachusetts from the
late 1800's until 1962 (Payne and Selzer 1989). Since the enactment
of the Marine Mammal Protection Act in 1972, harbor seals have more
than doubled their numbers in southern New England (Payne and Schneider
1984).
In southern
New England, harbor seals occur mainly from late September through May
(Schneider and Payne 1983). Following May, they move northward and are
found along the coast of Maine and eastern Canada (Whitman and Payne
1990). By the end of November, many seals leave their more northern
habitats with great numbers traveling to the Cape Cod area (Katona et
al. 1993). Harbor seals are abundant in the waters off Cape Cod during
the winter and spring (Payne and Selzer 1989) although periodic sightings
also occur in the summer and fall (Center for Coastal Studies, unpublished
data).
Feeding
Analyses of fecal samples from harbor seals indicated that the main
prey item for this species in the Cape Cod area is sand lance, Ammodytes
(spp.) (Payne and Selzer 1989). Overall, though, harbor seals are considered
to be opportunistic feeders and tend to forage on fish and squid species
that are regionally and seasonally abundant, showing a preference for
small schooling fishes (Payne and Selzer 1989).
Reproduction
Presently in New England, no pupping ledges are known to exist south
of Maine (Payne and Selzer 1989). Adult females commonly pup in the
same area in which they were born. Pups are born from mid-April to mid-June
and generally, are weaned within 4 to 6 weeks (Wilson 1978). Shortly
after weaning, females will mate again. Both sexes are thought to reach
sexual maturity by the age of 6 (Boulva and McLaren 1979). Segregation
by both sex and age class has been reported at haul-out sites during
the breeding season in many locations (see Kovacs et al. 1990). However,
along the beaches of Sable Island, Nova Scotia, there was no evidence
of segregation by age, sex or breeding condition (Godsell 1988). Breeding
males are known to display while in the water which may be attributed
to territory defense or possibly self-advertising (Perry et al. 1993),
although Godsell (1988) found that such displays or fights did not appear
to influence male haul-out patterns.
Group
Size and Composition
Little information exists regarding the social structure or group composition
of harbor seals in the Cape Cod region. According to Whitman and Payne
(1990), younger seals appear to occupy mainly the outer parameters of
breeding areas and they found that, in the waters surrounding Cape Cod,
95% of the seals were juveniles (less than 1 year) and subadults (less
than 4 years). Data on harbor seals inhabiting rock haul-out sites indicate
that they create hierarchies based on size and sex with territorial
adult males dominating all other sex and age classes while protecting
their preferred sites (Sullivan 1982). Whitman and Payne (1990) reported
that dominant males appeared to displace subadults of both sexes on
rock haul-out sites after weaning occurs and competition for receptive
females begins to increase. This displacement of subordinate subadults
and juveniles may explain somewhat their great abundance in the Cape
Cod area.
Grey Seals
General
Description and Status
Grey seals, Halichoerus grypus, are the largest seals seen in
the Stellwagen region with any frequency. They reach up to 8 feet in
length and are most often recognized by their long, straight snout which
gives them a horse-shaped head. A frontal view of the nostrils reveals
a "W" shape unlike the "V" shape appearance of the
harbor seal. There are no current population estimates for grey seals
in the Gulf of Maine but their numbers appear to be increasing.
Distribution and Abundance
The western North Atlantic grey seal ranges from the Labrador coast
southward to Nantucket with the main concentration found around the
Gulf of St. Lawrence (Bonner 1990). In the early 1960's, the Massachusetts
population of grey seals was thought to number around 20 animals as
a result of bounty hunts (Shurman 1986). Presently, that remnant population
is located southwest of Nantucket Island and is the only active breeding
colony off the eastern coast of the United States (Payne and Selzer
1986). In recent years, sightings of grey seals in Massachusetts waters
(including the Stellwgen Bank region) have become more frequent which
is probably due to animals
immigrating from the expanding Canadian stock (Katona et al. 1993).
The majority of grey seal
sightings in Cape Cod Bay and the Stellwagen Bank area occur during
the winter and spring, although periodic sightings have been recorded
in the summer (Center for Coastal studies unpublished data).
Feeding
Grey seals prey mostly on fish but will also forage on invertebrates
(Katona et al. 1993). In the Nantucket area, grey seals are thought
to feed on skates, Raja spp., alewife, Alosa pseudoharengus,
and sand lance, Ammodytes spp. (Shurman 1983).
Reproduction
In the northwest Atlantic, pups are born in January and February, either
on land or on ice (Bonner 1990). Nursing lasts for 2 to 3 weeks and
breeding occurs shortly after weaning (Bonner 1990, Katona et al. 1993).
Data from Sable Island, Nova Scotia, suggest that females return to
the same beach area to pup from year to year (Bones and James 1979).
Bones and James (1979) also reported that males did not appear to defend
territories or form dominance hierarchies but instead competed for the
right to stay within the aggregation of receptive females. Males that
failed to establish themselves with receptive cows tried to intercept
females returning to the sea at the end of the breeding season, but
appeared not to be as reproductively successful. Studies of grey seals
around Great Britain indicate that both sexes exhibit fidelity to previous
breeding sites (Amos et al. 1993, Twiss et al. 1993). Amos and others
(1993) found that 30% of pups born to the same female in different years
were full siblings, which may be partly due to this high degree of site
fidelity. Amos and others (1993) also reported that this species breeds
colonially in remote areas around the British Isles and that males compete
aggressively for receptive females and even though the dominant males
are generally more successful, subordinate males do gain some access
to females. This was attributed to subordinates either being able to
"sneak" access to females or, perhaps, that some females are
fertilized outside of the breeding colony.
Group
Size and Composition
Information regarding the social structure or group composition of grey
seals in the Cape Cod area is not available.
continue
to next section
