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| Marine Mammals | • | Cetaceans | • | Pinnipeds |
A marine mammal could be defined as any mammal that makes the sea home for part of or all of its life. The category includes cetaceans, pinnipeds, sirenians (dugong and manatees), marine mustelids (sea otter) and the polar bear. Marine mammals, as well as terrestrial mammals, are in the class Mammalia, which includes more than 4000 species. Mammals are warm-blooded and have hair; female mammals give birth to live young and have mammary glands that secrete milk to nourish their offspring.
Cetaceans
What are cetaceans?
Cetaceans are mammals that have adapted their bodies and behaviour to live in the water. Their streamlined and elongated shape offers minimum resistance in the aquatic environment. They lack external hind limbs and the forelimbs have been drastically modified into flippers, which vary in size and shape. They propel themselves through the water using the muscular tailstock. A thick layer of fat or blubber just beneath the skin helps reduce heat loss from the body core and also acts as an energy reserve. Cetaceans spend their entire lives in the water. Unlike marine mammals such as seals and other pinnipeds that must breed on dry land, cetaceans feed and breed in the ocean.
Toothed and Baleen Cetaceans
There are about 83 species of cetaceans in the world, classified in two main groups (suborders):
Toothed Cetaceans (odontocetes):
This group of cetaceans have teeth and a single blowhole. The group includes beaked and sperm whales, river and ocean dolphins, porpoises and monodontids (which means 'one-toothed', with only two species, beluga and narwhal). They use echolocation to locate their prey, which include fish, squid and sometimes, as in the case of killer whales (Orcinus orca), other marine mammals.
 Common dolphins (Delphinus delphis). |
Baleen Whales (mysticetes):
| Members of this group have baleen instead of teeth and have two blowholes. Baleen consists of rows of fibrous plates that strain zooplankton, fish and invertebrate prey out of the water column. The world's largest mammal, the blue whale (Baleanoptera musculus), belongs to this group. Minke whales (Balaenoptera acutorostrata) frequent Irish waters and can be often viewed from the coast. |  Minke whale (Balaenopter acutorostrata). |
Distribution maps of some of the cetacean species in Irish waters
| Of the 28 species of cetaceans recorded in northwest European waters, 23 occur in Irish waters. The distribution maps shown in the atlas however, only display the occurrence of 13 species: the Bottlenose Dolphin, the Common Dolphin, the Fin Whale, the Humpback Whale, the Harbour Porpoise, the Killer Whale, the Minke Whale, the Pilot Whale, the Rissos Dolphin, the Striped Dolphin, the Sperm Whale, the White-beaked Dolphin and White-sided Dolphin. |
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Protection of Cetaceans
All cetacean species occurring in European waters are now afforded protection as Annex IV species under the EC Habitats Directive and deliberate capture, killing or disturbance of these species is illegal. Two species, the bottlenose dolphin (Tursiops truncatus) and the harbour porpoise (Phocoena phocoena) are Annex II species (species of Community interest), whose conservation
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Other legislation at different levels that protect cetaceans include: the Bern Convention (1979) on Conservation of European Wildlife and Natural Habitats, and the Bonn Convention (1979) on Conservation of Migratory Species; the Agreement on Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS, 1991); the International Convention for the Regulation of Whaling (1946); and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, 1973).
Pinnipeds
What are pinnipeds?
Pinnipeds are highly modified carnivorous mammals, which have adopted an aquatic life and form a similar group of about 33 species from three families, true seals (Phocidae), eared seals (Otariidae) and the walrus (Odobenidae). Seals body shape and limbs are modified for their aquatic habitat, the streamline shape offers minimum resistance to movement in water and the limbs, with no supporting function, are modified into flippers. The two species of seal that breed in Ireland belong to the family Phocidae. In common with other true seals, they lack external earflaps and have flippers that are covered in hair.
Harbour Seals (Phoca vitulina):
Like their larger grey seal relatives, harbour (or common) seals have established
themselves at terrestrial colonies (or haul-outs) along all coastlines of
Ireland, which they leave when foraging or moving between areas, and to
which they return to rest ashore, rear young, engage in social activity,
etc. These haul-out groups of harbour seals have tended historically to
be found among inshore bays and islands, coves and estuaries (Lockley, 1966;
Summers et al., 1980), particularly around the hours of lowest
tide. Harbour seal distribution in Ireland is predominantly along the west coast with highest concentrations in counties Donegal, Sligo, Mayo, Galway, Cork and Kerry.
A national census of the harbour seal was carried out in 2003, resulting in an up-to-date population estimate for the species (Cronin et al., 2004). Harbour seals are best counted during the annual moult (August-September), when the largest and most consistent part of the population is ashore. The estimate of approximately 2,900 harbour seals refers to the number of animals ashore during the census and does not account for seals that were at sea at the time of the survey, and therefore unavailable for counting. The estimate of 2,900 is referred to therefore as a minimum population estimate.
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Click here to view a map of Harbour Seal distribution. |
| A national census of the
harbour seal was carried out in 2003, resulting in an up-to-date population
estimate for the species (Cronin et al., 2004). Harbour seals
are best counted during the annual moult (August-September), when
the largest and most consistent part of the population is ashore.
The estimate of approximately 2,900 harbour seals refers to the number
of animals ashore during the census and does not account for seals
that were at sea at the time of the survey, and therefore unavailable
for counting. The estimate of 2,900 is referred to therefore as a
minimum population estimate. |
Harbour Seal Census
using Thermal Imagery |
Grey Seals (Halichoerus grypus):
Up
to one third of the world's population of grey seals occurs in the North
East Atlantic, the majority of which breed in Scotland. The existing population
estimate of 2,000-2,500 grey seals in Ireland (Summers, 1983) is outdated
and numbers from more recent local or regional population surveys indicate
that the national grey seal population size is considerably greater today
than was estimated in 1983 (Ó Cadhla & Mackey, 2002); this is
currently being addressed with a population census planned for late 2005.
Unlike harbour seals, grey seals favour more exposed parts of the coast
at which to come ashore. The largest breeding colonies in Ireland are on
the exposed offshore islands off the west and south-west coasts of Ireland,
namely the Blasket Islands Co. Kerry and the Inishkea Islands, Co. Mayo.
Grey seals also breed on some islands off the east coast such as Lambay
Island, Co. Dublin and the Saltee Islands, Co. Wexford and on exposed parts
of the mainland coasts of Co. Donegal and Co. Mayo.  Aerial view of grey seal pups and adults. |
Protection of Seals
Grey and harbour seals are strictly protected in the Republic of Ireland under the Wildlife Acts, 1976 and 2000. They are listed under Annex II of the EU Habitats Directive as species of Community Interest, whose conservation requires the designation of Special Areas of Conservation (SACs). In the latter part of the 1990s, the National Parks & Wildlife Service, NPWS (formerly part of Dúchas the Heritage Service) proposed all of the known major breeding sites of the two species as SACs, ten for the grey seal and seven for the harbor seal.