The waters north and west of Scotland, encompassing the Shetland and Orkney Isles and Outer Hebrides are probably the richest of all sea areas in Europe for cetaceans; species recently recorded include the humpback whale, fin whale, sei whale, minke whale, sperm whale, Northern bottlenose whale, Cuvier's beaked whale, Sowerby's beaked whale, harbour porpoise, common dolphin, Atlantic white-sided dolphin, white-beaked dolphin, killer whale, false killer whale, long-finned pilot whale, Risso's dolphin and beluga (Evans 1994) (Evans 1995) (Evans 1992). In the past year, blue whales have also been detected (acoustically) in waters west and north of the British Isles (Tasker pers. comm.). Large numbers of cetaceans appear to be present in these waters (Bloor et. al. 1996).

These waters are highly productive - marine productivity is high in areas where water with different properties meets to form fronts. Islands and steep bottom topography enhance mixing, and enriched waters result in high plankton productivity. West of the British Isles, the warm waters of the Gulf stream meet cooler coastal waters, providing good conditions for primary production in the waters of the Atlantic fringe (Evans 1990). The waters off the Hebrides and Shetland are known to be important fish spawning areas for herring, sprat, whiting, gadoids (which spawn west of the outer Hebrides) and sandeels. Mackerel migrate along the continental shelf edge between spawning grounds west of Ireland and northern feeding grounds (Evans 1990) (Evans et. al. 1993).

The continental shelf edge runs north and west of Shetland. This is widely accepted to be an important migration route along which many of the great whales travel during their long migrations from breeding areas to the south and west of Britain to feeding areas to the north. The bathymetry of the area (see fig. 1), with deep water, trenches, ridges and island platforms and a wide variety of bottom topographical features mean that a variety of pelagic species are present in the area either during migration or for more extended periods. High productivity and food resources such as plankton, fish and cephalopods, support a large marine mammal community, including seabirds as well as seals and cetaceans. Many cetacean species are known to favour areas with steep bottom topography.

The importance of the European continental shelf edge to cetaceans is confirmed by whaling data from earlier this century. Whalers, operating from stations in the Hebrides and Shetland, took large catches of whales, up until the 1950's in some cases. There are also more recent indications of the areas importance to cetaceans. Analysis of the JNCC's cetaceans sightings database indicates that the Hebrides appear to be an area of high cetacean density throughout the year, and high seasonal concentrations of some species occur around Orkney and Shetland and in the waters between the Shetland and Faroe Islands (Northridge et. al. 1995) (Bloor et. al. 1996). Incidental sightings from around Britain and Ireland, and recent (as yet unpublished) acoustic data indicate that some large baleen whales such as fin, sei, humpback and even blue whales may be returning to former feeding grounds and migration routes (Evans 1992) (Evans and Scanlan 1989). Rare sightings, such as that of a Northern right whale in deep water off the Outer Hebrides, west of Harris (Evans 1981) provide a glimmer of hope that even this critically endangered species might still occasionally pass through British or Irish waters.

Gunnlaugsson and Sigurjonsson (1990) and Sigurjonsson et. al. (1989) report sightings of fin, minke, killer, sperm, a humpback and bottlenose whales during surveys north of Shetland, west of the Outer Hebrides and around the Faroes. In addition, blue, humpback and sei whales were sighted south and east of Iceland. Several right whales (and calves) have been sighted south-west of Iceland. Blue, fin, minke, sperm northern bottlenose, killer, pilot and humpback whales were also recorded off the south-east coast of Iceland (Sigurjonsson et. al. 1991). There are some indications that the distribution of unusual and little known beaked whales such as Sowerby's beaked whale distribution may be centred on Norwegian Basin and adjacent Faroe-Shetland Channel (Evans 1980).

Although the data is presently very patchy, there is a good deal of evidence, both historical and contemporary, to support the notion that waters of the Atlantic fringe are important to cetaceans. Sperm whales, fin whales, minke whales, northern bottlenose whales and sei whales, depleted by commercial whaling and of unknown status, are still regularly documented here. Long-finned pilot whales, killer whales, white-beaked and white-sided dolphins, harbour porpoises and common dolphins appear to be widespread throughout the region.