| Nature - Wildlife |
|
Common Seal |
Classification and names
Marine mammal, order: Carnivora (predators), family: Phocidae
Other and local names:
In English also: common seal
In French/Français: le veau marin
In German/Deutsch: Gemeiner Seehund
In Dutch/Nederlands: gewone zeehond
Description
Torpedo-shaped body with small head. An important difference with the grey seal
is that the harbour seal has V-shaped nostrils.
Colour: varies grey to brown-grey, with black spots.
Underside a little lighter. Young are born with a steel grey fur and have already
lost their white fur before birth. Sub-adults have a sand coloured fur.
Length: males 150-190 cm, females 120-155 cm, new-borns
70-90 cm
Weight: males 55-130 kg, females 45-105 kg, new-borns
9-11 kg
Distribution
In general, four different sub-species of the harbour seal (Phoca vitulina)
are distinguished: the eastern Atlantic harbour seal (P. v. vitulina),
de western Atlantic harbour seal (P. v. concolor), the western Pacific
harbour seal (P. v. stejnegeri), and the eastern Pacific harbour seal
(P. v. richardsi).
Within Europe, the eastern Atlantic harbour seal (P. v. vitulina) can
be found around the British isles and Ireland, in Kattegat-Skagerrak, in the
south-western part of the Baltic Sea, in the Wadden Sea and along the North
Sea coasts of Denmark, the Netherlands and Brittany (France).
The most northern distribution of the harbour seal coincides with the most northern
ice-free waters in the Arctic region, along the western coast of Prins Karls
Forland (Spitsbergen). The relatively high temperature there is caused by the
warm Gulf Stream. The harbour seal is also present in the waters around Iceland,
along the Norwegian coast and the coast of Kola peninsula (Russia).
Migration: can travel hundreds of kilometres and settle
elsewhere. Preliminary results with marked individuals show that 70% of weaned
pups stay in the area they where marked, for older seals this figure is 90%.
Habitat
Common seals use a variety of coastal habitats: both rocky and sandy coasts.
Rocky coasts are especially used in the tidal areas sheltered from the open
sea. Intertidal rocks on offshore islets are particularly favoured. Reefs and
pebble beaches are also used for hauling out where they are free from human
disturbance. In the Baltic they use beaches in the vicinity of the sea-cliffs.
Sandy beaches along tidal coasts and in estuaries are also used, e.g. in the
Wash (England) and the Wadden Sea.
Both inshore and offshore waters are used for foraging. Foraging habitats around
the North Sea are mainly shallow sandy or muddy sea bottoms.
Important criteria for the selection of haul-out sites, used for resting, breeding
and moulting, include the absence of human disturbance and access to deep water.
Food
Common Seals feed on most fish species available, within relatively distinct
feeding habitats, rather than preferring specific prey species. Therefore, the
diet varies considerably, both in time and in space. Feeding occurs predominantly
in inshore waters on a wide variety of fish species, such as Flounder (Platichthys
flesus), Sole (Solea vulgaris), Herring (Clupea harengus),
Cod (Gadus morhua), Whiting (Merlangius merlangus) and Sand eel
(Ammodytus spp).
Behaviour & Reproduction
Feeding: In general, harbour seals forage around their
breeding sites throughout the year. However, this can be 60 km from the haul-out
sites. The animals travel quickly and directly to the preferred localities,
and remain in defined areas. Trips typically last 1-5 days and most active feeding
occurs at night. Seals are present at local haul-out sites throughout the year.
Dives 2-10 minutes in shallow waters (10 m).
Sociability: solitary, but can be found in groups
up to 500 animals. Group size is variable, and local differences between groups
are maintained over long periods. Group size may be related either to the size
of the haul-out site or foraging areas (food availability), or to site fidelity.
Vocalising: pups sometimes make crying noises. Males
slap the water with their flippers to threaten. Example
1, Example 2
Mobility: can swim up to 35 km/h, movement on land
difficult, can dive up to 500 m
Specifics: can sleep on land as well as in/under water,
young are able to swim directly after birth
Sexual maturity: females become mature at 3-5 years
of age, males at 5 years
Reproduction capacity: around the North Sea on average
87% of females are pregnant each year
Reproduction period: the actual pregnancy is 7 months,
but for seals it may take 3 months for a fertilised egg to implant in the uterus.
Young are born from May to July, with a peak in the second part of June.
Nursing period: weaned at 3-6 weeks when young reach
a weight of about 24 kg
Life span: females on average 38 years, males on average
25 years.
Predation and competition
Not much is known about competition with other marine top predators or about
predation. Depending on the habitat type there is some dietary overlap with
Black cormorants (Phalcrocorax carbo). There may also be some dietary
overlap with the Grey seal (Halichoerus grypus); spatial overlap with
foraging areas of grey seals can occur.
Protection
The Common seal is protected though:
There is no risk of extinction at present, although the Common seal population in the Baltic is considered vulnerable due to its small size.
Population size
Historically, hunting and later pollution (e.g. PCB's) have had the greatest
impact on population size. In 1987, the total population of P. v. vitulina
in the eastern Atlantic was estimated to be at least 75,000. As a result of
the Phocid Distemper Virus (PDV) infection in 1988 local populations were severely
depleted but recovered well, and were estimated at 70,000 in 1992. The 1997
level of at least 72,000 is close to the pre-epizootic level.
Sources & further reading:
P.J.H. Reijnders et al., Status of Pinnipeds relevant to the European Union,
IBN
Scientific Contributions 8, Wageningen 1997.
The Atlas of European Mammals. T & D Poyser Natural History.