Report 301
Cetacean observations during seismic surveys in 1998
(2000)
Stone, C.J.
Recording of cetaceans during 1998 operations in UK waters and some adjacent areas, in compliance with the Guidelines for minimising acoustic disturbance to marine mammals from seismic surveys (April 1998), yielded a total of 518 sightings comprising 4,175 individuals. There were only four sightings of seals. The total time spent watching for marine mammals during seismic surveys in 1998 was 15,834 hrs 21 mins.

Summary

 
The most frequently seen species was the pilot whale.  Fin whales, sperm whales, white-sided dolphins, common dolphins and minke whales were also seen in moderate numbers, with lower numbers of other species.  Sightings of cetaceans peaked in July, with most occurring in waters to the north and west of the UK, which reflected the location and timing of surveys.
 
Allowing for factors such as geographical distribution, seasonal variations in sightings, weather conditions and the power output of the airguns, the sighting rate of all baleen whales combined was found to be higher when the airguns were firing during seismic surveys.  It was thought that this could possibly reflect an increased tendency to remain near the water surface during periods of shooting, and thus be more visible.  Sighting rates of fin whales, fin/ sei whales, sperm whales, pilot whales, all dolphins combined and white-sided dolphins did not differ significantly with seismic activity.
 
Recommendations for future revisions to the guidelines are made.  Such revisions might include a maximum duration of the soft-start, action to be taken if marine mammals are detected during the soft-start, prohibition of unnecessary shooting, extra protection for vulnerable species, and consideration of the effects of time-sharing.
 
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ISSN 0963 8901
 
Please cite as: Stone, C.J., (2000), Cetacean observations during seismic surveys in 1998, JNCC Report 301, ISSN 0963 8901