Marine Mammals

Eurasian otter

THOUGH the Eurasian otter is an aquatic rather than a truly marine mammal, we shall include it here because a significant proportion of Ireland's population inhabits the coastal zone, where they spend part of their lives on land and the remainder at sea, whilst depending on both.

With their webbed toes, streamlined body and dense waterproof coat of fur, otters are well adapted to an aquatic way of life. They feed on a variety of aquatic prey, including fish, eels, crabs and other crustaceans, and to a lesser extent frogs and birds. Much of Ireland's extensive low rocky shore environment provides ideal habitats for coastal otter populations, which often breed and rear their cubs (usually two per litter) within easy reach of the shore.

Pinnipeds (seals)

The common seal, sometimes referred to as the harbour seal, is a coastal species that inhabits sheltered waters around Ireland. It occurs most frequently along the north, east and southwest coasts, being less abundant in the west. They prefer to feed on fish, both bottom-dwelling and free-swimming, and some invertebrates in narrow channels near the mouths of bays. At low tide they haul out onto skerries (rocky islets and reefs) or sand banks to rest and digest their food. Common seals are gregarious, preferring to live in groups, probably made up of related animals. Around Ireland, common seals give birth during June and July. The single pup, which is able to swim within just a few minutes after its birth, suckles for between 3-6 weeks.

The grey seal is also a coastal species, though it may forage further out at sea than the common seal. It is sparsely distributed around Ireland and widely dispersed outside the breeding season. Grey seals feed on a wide variety of fish and some invertebrates. Adults congregate to form herds during the late summer to autumn breeding season. One of Ireland's largest herds (about 200 individuals) hauls out to breed on the Blasket Island group in County Kerry, especially the White Strand (An Trá Bhán) on the Great Blasket Island, and on the shores of Beginish. The other main Irish breeding group is centred on the remote Inishkea islands off the coast of northwest County Mayo, while other much smaller rocky shore breeding sites are dotted around the coast.

Unlike common seals, the single grey seal pup is born in white lanugo (natal coat). Lactation lasts for 2-3 weeks before the mother abandons the pup, around which time it begins to moult its lanugo. The pup spends another two weeks or so on land while it moults before entering the sea when it must learn to forage efficiently before its body fat reserves are depleted. Recent research by the UK Sea Mammal Research Unit suggests that grey seal pup mortality is high, with approximately 50 per cent of newborn pups dying during the first year (Seal Conservation Society, 1998).

Cetaceans (porpoise, dolphins and whales)

Twenty-three cetacean species have so far been identified in Irish waters, of which eleven are frequently recorded.

The harbour porpoise is considered to be the most abundant species and has been recorded on all coasts but is especially abundant off southwest Ireland, where an estimated 20,000 may occur in summer (Leopold et al., 1992). This, together with a population in the southern Irish Sea, represents an important part of the overall North-East Atlantic population, which is considered to be vulnerable (Simmonds et al., 1997). Sightings made in deeper waters above the Rockall and Faroe Banks show that the species is not just restricted to shallow shelf waters, as was previously thought. A survey conducted in July 1994 confirmed that the harbour porpoise is present throughout most of the Celtic Sea shelf area.

There is considerable genetic and other evidence to indicate that harbour porpoises live in discrete populations with little movement between them (Simmonds et al., 1997). The harbour porpoise is relatively short-lived (average life span is only nine years). They are known to calve off the southwest and east coasts of Ireland between June and September (Irish Whale and Dolphin Group, 1993). Their low reproductive rate, typical of all cetaceans, makes them especially vulnerable to threats.

The bottlenose dolphin is the other most frequently sighted cetacean in Irish waters. They are most commonly seen in coastal waters, though they are frequently reported further out at sea, especially in the Celtic Sea shelf area. Anecdotal evidence suggests that, historically, bottlenose dolphins used to frequent various Irish estuaries and other inshore waters where they are now no longer (or very rarely) seen. It has been suggested that a major decline in the species, dating from as early as the 19th century, may have occurred. As the human population has increased (accompanied by industrial pollution, expanding fisheries, coastal development and habitat disturbance), so bottlenose dolphin populations seem to have declined (Simmonds et al., 1997).

Work by researchers in the UK suggests that bottlenose dolphins in European waters typically form well-established groups of some 130 individuals, comprising several sub-pods. A bottlenose dolphin group off Cornwall and Devon has been found to have a large home range of several hundred kilometres of coastline, which may be typical. This group also appears to travel more in the spring and summer than at other times.

The discovery of this extensive range ... has very significant implications for their conservation as it challenges the view that their conservation can be simply addressed via small "protected areas". (Simmonds et al., 1997)

Bottlenose dolphins are known to calve in Irish coastal waters, including the funnel-like mouth of the Shannon Estuary, which is a clearly identified home range, summer calving and nursery ground for a group of about 100 bottlenose dolphins. Consequently, the Mouth of the Shannon is of very high European conservation importance.

Both the harbour porpoise and bottlenose dolphin are listed in Annex II of the EU Habitats Directive as species that not only require strict protection but also warrant designation of Special Areas of Conservation (SAC).

Other "small cetaceans" in Irish waters are usually animals that are oceanic in habit and hardly ever come into inshore waters. The common dolphin is one of the most abundant cetacean species found off the south and southwest coasts and is frequently observed in the Irish Sea and on the Celtic Sea shelf.

The white-beaked dolphin and Atlantic white-sided dolphin frequently occur offshore where they feed on a variety of pelagic fish species. White-beaked dolphins may move closer to shore in summer, although they are most usually found over the continental shelf area. Atlantic white-sided dolphins have been shown to calve off the southwest coast during early summer. Their distribution seems to be closely related to that of blue whiting — an important prey species for them.

In recent years there has been an increase in sightings of the striped dolphin in Irish waters. This species prefers warmer waters and the increase in sightings may relate to changes in the warm water currents of the North Atlantic Drift.

Risso's dolphin has a wide distribution, mainly off the west coast of Ireland, though they are occasionally reported in the Irish Sea. This largely oceanic dolphin has been shown to calve in Irish waters in late spring and early summer.

The long-finned pilot whale is the most commonly observed "whale" species in Irish waters (though it is technically a "small cetacean" because it does not yet come under formal International Whaling Commission jurisdiction). Although mainly inhabiting waters of the deep open ocean, where they feed principally on squid, large numbers have been recorded along the edge of the continental shelf west of Ireland. The waters off southwest Ireland are thought to be an important breeding ground for this species (Evans, 1980).

The orca, or killer whale is a frequently recorded species in Irish waters, being observed in small numbers, especially off the west coast.

Of the baleen whales, the minke whale and fin whale are the most frequently observed in Irish waters. The minke whale is widely distributed along the Atlantic seaboard and is reported sporadically in the Irish Sea. It is the baleen whale most frequently seen from land. Minke whales that over-winter in warmer waters, such as near the Azores, may regularly return to feed in Irish waters where they may also breed. Others pass through Irish waters on migration to the rich sub-arctic summer feeding grounds. Fin whales also migrate through Irish waters along the edge of the continental shelf from breeding grounds at lower, warmer latitudes to summer feeding grounds in the sub-arctic. It is thought that some fin whales (possibly a genetically discrete sub-population) may in fact breed off the south coast of Ireland.

Other baleen whales reported or believed to transit through Irish waters on migration along the shelf edge are the sei whale, humpback whale, the rare blue whale and possibly the even rarer northern right whale.

As for the toothed whales, the deep-sea to the west of the continental shelf provides suitable habitats for deep-diving species such as the sperm whale and various beaked whales (Ziphiidae). There is evidence that sperm whales may be occurring more frequently off the Irish coast (Berrow et al., 1993), but many of the beaked whales, apart from the northern bottlenose whale, have never been seen alive and are known only from stranded carcasses. Six of the nine European records of True's beaked whale are from the west coast of Ireland and a recent stranding of a Gervais' beaked whale was only the second record for Europe (Bruton et al., 1989).

The northern bottlenose whale inhabits deep ocean waters and is very occasionally seen in Irish territorial waters along the continental shelf edge where they feed on squid and other deep-sea animals. The International Whaling Commission classifies the North-East Atlantic population as a Protection Stock due to its depletion (by commercial whaling) and continued vulnerability.

Commercial whaling by Europeans and Scandinavians from the late 16th century through to the 20th century — peaking in the late 19th century with the introduction of modern whaling technology such as harpoon cannon, exploding harpoons, steam then diesel driven catcher vessels and factory motherships — has depleted most North-East Atlantic populations of "great whales" and some small cetacean species.

The North-East Atlantic populations of blue, fin, sei, humpback, right and sperm whales were further depleted between 1908 and 1923 by commercial whaling operations in Irish waters undertaken from Norwegian owned shore stations in County Mayo. Commercial whaling operations for northern bottlenose whales by Norwegian vessels are thought to have continued in waters to the northwest of Ireland until 1973. In recent years, whaling interests in the Faroe Islands have sought to establish a commercial hunt of between 200-400 northern bottlenose whales annually.

Long-finned pilot whales, including those which transit through offshore Irish territorial waters, continue to be subject to a drive-fishery in the Faroe Islands with as yet undetermined long-term consequences to the overall North-East Atlantic population and constituent, genetically discrete sub-populations.

Likewise the North-East Atlantic minke whale population is subject to an increasingly large-scale commercial whale hunt by Norway during the summer whaling season. Some of these minke whales may seasonally migrate through Irish waters — either along the Atlantic seaboard or else through the Irish Sea. In 2002 Norwegian whalers caught 634 minke whales from a self-allocated quota of 671; the 2003 self-allocated quota is 711 minke whales. Whaling interests in Norway are currently pushing for quotas approaching 2,000 minke whales annually, plus government-approval for takes of other species, including fin whales. During 2002, Iceland rejoined the International Whaling Commission; it has expressed its long-term aim to resume hunting minke, sei and fin whales, and has even mentioned taking humpback and blue whales once their North Atlantic populations have "recovered"!

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