Report 228
Marine mammal observations during seismic surveys in 1996
(1997)
Stone, C.J.
Cetacean sightings were recorded during seismic surveys in 1996

Summary

 
1. Cetacean sightings were recorded during seismic surveys in 1996, in compliance with the Department of the Environment's Guidelines for minimising acoustic disturbance to small cetaceans. A total of 236 sightings of cetaceans, comprising 1,315 individuals, were reported.
 
2. The most abundant species were white-sided dolphins, white-beaked dolphins, pilot whales, killer whales and fin whales. Sightings peaked during July and August and were concentrated to the west of Shetland, in the northern North Sea and to the west of Ireland. Large whales and white-sided dolphins were found mainly to the west of Shetland, while white-beaked dolphins were found in the North Sea.
 
3. After taking account of the proportion of time spent shooting, sightings of fin whales were more frequent when the airguns were firing, while sightings of white-beaked dolphins were less frequent when shooting was taking place. White-sided dolphins were also seen less frequently when the airguns were firing, but this was not significant. More frequent sightings of whales seen when shooting could reflect the greater ease of detecting cetaceans in the calmer weather conditions necessary for shooting.
 
4. Although numbers of cetaceans declined after August, this was not thought to be a result of prolonged seismic activity. Any disturbance seemed to be only temporary, with cetaceans rapidly appearing in the survey areas between periods of shooting.
 
5. Nearly all species were found to be further from the airguns when the guns were firing than when they were not, although this was only statistically significant for fin whales and white-sided dolphins.
 
6. Few cetaceans came towards the ship or crossed its path when the airguns were firing. Cetaceans were observed actively feeding both when the airguns were firing and when they were not, although those seen feeding when the guns were firing were at a greater distance. Positive interactions with the survey vessel were rare when the airguns were firing.
 
7. Increasing depth may reduce the effect of seismic activity - relatively more fin whales were seen when shooting in waters of greater than 1,000 m depth than in shallower waters.
 
8. Sample sizes were small, therefore conclusions should be treated with caution.
 
9. Recommendations are made for revisions to the cetacean recording forms.
 
Download
You will need the free Adobe Acrobat Reader to view this document.
56 pages
ISSN 0963 8091
 
Please cite as: Stone, C.J., (1997), Marine mammal observations during seismic surveys in 1996, JNCC Report 228, 56 pages, ISSN 0963 8091