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Monitoring Marine Mammals

Cetacean

Background

There are two AFEN-funded projects examining the distribution of marine mammals in the Atlantic Margin. The first, is through sonar surveys, and the second is by visual surveying.

Sonar Survey

Marine mammals can be identified by listening for their sounds, which can travel considerable distance through the water and are comparatively unaffected by rough weather or night-time. AFEN is funding an innovative approach to listening for the large whales by contracting Cornell University to use military hydrophones (underwater microphones) arrays deployed during the cold war period to listen for submarines and other vessels (C.W. Clark and Charif,R.A. 1998)).

Chart

The project is managed by the Joint Nature Conservation Committee. These systems have proved particularly good at detecting the large whales which communicate using low-frequency sounds. Set against the advantages are difficulties such as the seasonal variation in amount of calling made by each species.

Listen to the Sound of the Sonogram

Next Follow this link to hear the whale sounds


Visual Survey

This, in conjunction with the mapping of seabirds, is described under Project 2: Seabirds; all marine mammals seen by biologists are recorded and can be mapped in a similar way to seabirds. These records have the considerable advantage over casual sightings of being effort-related. From these sources, it is possible to give indications of abundance and comparisons between areas. An atlas is being prepared in co-operation with the Sea Mammal Research Unit and the SeaWatch Foundation that will place these sightings in the wider context of NorthWest European waters. However, these surveys have their own limitations. For instance, no sightings can be made by night, and it is difficult to see many species if the sea is rough.

Early Results

Existing survey data suggests that two large baleen whale species - the fin whale and humpback whale - undertake regular seasonal migrations off the edge of the UK Continental Shelf in spring and autumn. However, it now appears that fin whales are present throughout the year, and no directed movements have been detected. Also, during spring and summer months the reported numbers of cetaceans increases.

On the UK Continental Shelf:

  • Harbour porpoises are the commonest species and occur in most waters except the English Channel and southern North Sea where they are rare.
  • White-beaked dolphins are common in the northern North Sea and to the north and west of Britain.
  • Minke whales are the most frequently seen whale species in the northern North Sea and to the west of Britain.

Cetaceans

In deep water to the west of Scotland:

  • Pilot whales are common, while harbour porpoises and white-beaked dolphins are uncommon.
  • White-sided dolphins are the commonest dolphin species.
  • Fin whales are the commonest whale.

To the south and west of Britain:

  • Common dolphins are the commonest species.
  • Species typical of the warmer parts of the Atlantic occur - such as striped dolphin.

Recent Results

These three sources of information have confirmed previous knowledge that the Atlantic Margin area is of great importance to the larger whales and to smaller marine mammals such as pilot whales and white-sided dolphins. The hydrophones project has shown that:

  • Blue whales which are thought to be extremely rare occur regularly in small numbers in these waters, mostly in winter, with a peak in November and December.

  • Humpback whales have only been detected acoustically between mid-November and March, although they have been sighted at other times of the year.

  • Fin whales are present throughout the year, with a lull in activity in May, June and July.
Fin Whale, © 2001 K Young/Sea Watch Foundation
© 2001 K Young/Sea Watch Foundation

Perhaps one of the more unusual findings of the sighting surveys was the discovery that hooded seals regularly feed in the deep water areas far to the north of Shetland. This species breeds on the arctic ice, particularly that east of Greenland, but the survey teams made positive identifications of individuals in the north of Shetland.

See also the Whales and Dolphins Conservation Society Pages

Offshore Working Practices for Seismic

There has been some concern over the interaction of seismic surveys and marine mammals in recent years. All seismic surveys in UK waters are undertaken in accordance with guidelines drawn up by staff working for the Joint Nature Conservation Committee after extensive consultation with industry, non-governmental bodies and others.

In order to further examine this issue, a workshop, partly sponsored by AFEN was held in June 1998 on the subject of marine mammals and seismic surveys.

Summary of Guidelines for Seismic Surveys

This record of environmental sensitivity has been achieved through strict observance of guidelines drawn up by the JNCC for UKOOA members and seismic contractors to follow, to minimise acoustic disturbance to marine mammals.

  • Survey vessels will not start up a survey line if cetaceans are seen within 500m or within 30 minutes of the survey's intended start time.
  • Survey vessels will wait for 20 minutes after the last sighting within this radius before proceeding to start guns.
  • Airgun array firing begins with a 'soft start' - a slow build up of power to allow cetaceans to leave the area.

See the JNCC web pages for guidelines on minimising acoustic disturbance to cetaceans during seismic surveys.


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