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Report: Seamounts of the Northeast Atlantic

The WWF/OASIS report "Seamounts of the Northeast Atlantic" is a unique product in reviewing the state of knowledge for a particular sea area - it was distributed globally to a very wide audience, covered in relevant media and the requests for copies indicated that it was well received.

There are at least some 800 major seamounts in the North Atlantic, mostly occurring associated with the Arctic Mid-Ocean Ridge, the Mid-Atlantic Ridge (MAR), and the Greenland-Iceland/Iceland-Faeroe Rise. However, there are also clusters of seamounts some distance from the MAR such as those along the south west of the Rockall Bank and west of Portugal on the Madeira-Tore Rise.

Water mass circulation is characterized by the warm North Atlantic Drift setting northeastwards, seasonal up welling off southeastern Europe and North Africa, and cold deep water formation off Greenland which then prevails in the North Atlantic deep sea. The Mid Atlantic Ridge, and in particular in the islands of the Azores, currents, water masses and species of different biogeographic origin meet and mix - shallow seamounts often acting as stepping stones for cross-Atlantic dispersal of species. Reproductive isolation between seamount ridge systems may also lead to elevated numbers of endemic benthic species, however this cannot yet be confirmed based on the limited data available.

Because of their volcanic origin and steep slopes amplifying the prevailing currents, hard substrata are common on seamounts. Softer substrata may also be present.

There is a paucity of information on the benthos, illustrated by the fact that a century of study has resulted in the identification of just 596 invertebrate species from all seamounts explored up to the late 1980 s. The enhanced currents that sweep around the seamounts and the exposed rock surfaces provide ideal conditions for suspension feeders, and it is these that often dominate the benthos.

Studies of the pelagic communities above seamounts reveal qualitative and/or quantitative differences when compared to the surrounding water. The higher biomass of planktonic organisms over seamounts constitutes an important basis for the diet of fish, squid and top predators such as sharks, rays, tuna and swordfish. Small and large cetaceans, and turtles also aggregate at these biologically productive hydrographic features.

The fish communities found around seamounts have evolved a suite of morphological, ecological, life-history and physiological features that enable them to successfully exploit an environment with enhanced currents and greater flux of organic matter than much of the deep sea. Many are adapted for strong swimming performance, deep-bodied and with relatively high rates of metabolism and food intake. They may also be exceptionally long-lived with a slow growth rate. Some are also subject to extremely high recruitment variability, with successful recruitment occurring on approximately decadal time scales.

The most significant threat in terms of geographic spread and scale of impact is commercial fishing. Commercially important species have been the targets of intensive exploitation using longlines, mid-water trawls and bottom trawls that can operate at depths of more than 1500m.

In most cases fishing has taken place before there is a reasonable understanding of the biology of the species being targeted, and in the absence of formal stock assessments or quotas. The result has been over-exploitation and major crashes in the different stocks.

Fishing activity is also known to have had a massive impact on the benthos of seamounts in other areas of the world ocean. However, for the North East Atlantic data on impacts are missing due to lack of scientific studies. Next to demersal fisheries, the use of longlines, driftnets and purse seines are known to have taken many thousands of seabirds, cetaceans, and turtles between them as “incidental catch”.

In recent years, several political initiatives are seeking to address the conflict between human impact and conservation requirements on a global, North East Atlantic regional and national level:
- The UN General Assembly called for urgent coordinated action to integrate and improve the management of seamounts and other underwater features in 2002,

- The need for conservation action in the high seas, i.e. by establishing high seas Marine Protected Areas is recognized by various fora (i.e. the Convention on Biodiversity)

- The OSPAR Ministerial Meeting agreed in 2003 on a regional priority list of species and habitats, including seamounts, for developing conservation action.

- The European Union Natura 2000 network of protected areas will include seamounts, selected as reef-like habitats under EU Habitats Directive Annex I. The first seamount protected is in Azores (Portugal) waters.

Methods and experiences gained with the management of human activities at seamount Marine Protected Areas in other parts of the world are complied in the final chapter.

Informations connexes

Reported by

WWF North-East Atlantic Marine Ecoregion (NEAME)
Am Guetpohl 11
28757 Bremen
Germany