Report 316
Marine mammal observations during seismic surveys in 1999
(2003)
Stone, C.J.,
There were 501 sightings of marine mammals (13,398 individuals) during seismic surveys in UK waters and some adjacent areas in 1999. 14,341 hrs 19 mins were spent watching for marine mammals during seismic surveys in 1999

Summary

 
There were 501 sightings of marine mammals (13,398 individuals) during seismic surveys in UK waters and some adjacent areas in 1999. 14,341 hrs 19 mins were spent watching for marine mammals during seismic surveys in 1999.
 
The most frequently seen species was the white-beaked dolphin. White-sided dolphins, sperm whales, minke whales and killer whales were also seen with moderate frequency, with lower numbers of sightings of other species. There were significantly more sightings of minke whales and white-beaked dolphins when compared to previous years. Sightings of marine mammals peaked in August, with most occurring to the west of Shetland and in the northern North Sea, which reflected the location and timing of surveys.
After allowing for potential sources of bias (location, season, weather conditions) the sighting rate of white-sided dolphins was found to be significantly lower during periods of shooting (excluding during low power site surveys). Sighting rates of minke whales, sperm whales, white-beaked dolphins and all dolphins combined did not differ significantly with seismic activity.
 
After taking account of weather conditions at the time of the sighting, white-beaked dolphins, all dolphins combined and all baleen whales combined were found to be significantly further from the airguns when they were firing than when they were silent (excluding site surveys).
 
Some effects of seismic activity on the behaviour of marine mammals were evident during seismic surveys (excluding site surveys). There was an increased tendency for cetaceans to engage in fast swimming and breaching, jumping or somersaulting during periods of shooting. This increased tendency was evident at distances of up to 4 km or more from the source for breaching, jumping or somersaulting, and at distances of up to 3 km for fast swimming. Positive interactions of cetaceans with the survey vessel or its equipment occurred significantly more often when the airguns were not firing.
 
When all cetaceans were combined, significantly more were found to be heading away from the vessel and fewer heading towards it during periods of shooting (excluding site surveys). More were also milling or travelling in various directions during periods of shooting. When all baleen whales were combined, significantly more were found to be heading away from the vessel during periods of shooting; for white-beaked dolphins and all dolphins combined significantly fewer were heading towards the vessel when the airguns were firing.
 
No significant effects of seismic activity were observed for site surveys, but sample sizes were low, precluding allowance for potential sources of bias such as weather conditions.
 
Both notification and a report were received by JNCC for 81% of seismic surveys taking place during 1999 (in blocks licensed in the 16th, 17th and 18th rounds of offshore licensing).
 
The duration of pre-shooting searches for marine mammals met or exceeded the required minimum of 30 minutes for 85% of occasions when the airguns were used during daylight hours in blocks where compliance with the guidelines was a licence condition. On 6% of occasions when the airguns were used during daylight hours in these blocks there was no pre-shooting search, while on 9% of occasions the pre-shooting search was shorter than the required minimum duration or was terminated prematurely. The proportion of short or absent pre-shooting searches was higher in other blocks. Short or absent pre-shooting searches occurred more frequently when fishery liaison officers or members of ships' crews were acting as marine mammal observers than when dedicated marine mammal observers were used; members of ships' crews were the least likely to perform an adequate pre-shooting search.
 
Excluding site surveys, 87% of soft-starts met or exceeded the required minimum duration of 20 minutes in blocks where compliance with the guidelines was a licence condition. Short or absent soft-starts were more frequent in other blocks. Short or absent soft-starts were more frequent when dedicated marine mammal observers were not present.
 
Marine mammals were seen within 500 m of the airguns shortly before shooting was due to commence on seven occasions in blocks where compliance with the guidelines was a licence condition. The guidelines require that in such circumstances shooting should be delayed for a minimum of 20 minutes after the animals are last seen; on two of the seven occasions no action was taken to minimise disturbance to the marine mammals and shooting commenced shortly after they were seen, while on a third occasion the delay was shorter than the minimum required and the subsequent soft-start was also short.
 
Dedicated marine mammal observers were much more efficient at detecting marine mammals than other personnel - mean sighting rates for dedicated marine mammal observers were more than eight times higher than that of other personnel. Dedicated marine mammal observers also made fewer errors when completing the recording forms.
 
The proportion of seismic surveys using dedicated marine mammal observers has steadily increased since the introduction of the guidelines, although in 1999 it was still only on a minority of surveys that such observers were used. The use of dedicated marine mammal observers is recommended, both in terms of compliance with the requirements of the guidelines and the provision of accurate data. Sole reliance on members of ships' crews to carry out observations of marine mammals was found to be the least effective alternative.
 
Revised standard recording forms are proposed in line with comments and suggestions received. A number of items for consideration when the Guidelines for minimising acoustic disturbance to marine mammals from seismic surveys are next revised are discussed.
 
Low sample sizes for many species limited the use of the data. It is recommended that the next analysis performed combines data from 1998, 1999 and 2000. As the recording forms have remained the same throughout these three years this would provide an opportunity to increase sample sizes, both for individual species and for site surveys.
 
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ISSN 0963 8091
 
Please cite as: Stone, C.J.,, (2003), Marine mammal observations during seismic surveys in 1999, JNCC Report 316, ISSN 0963 8091