Report 322
Marine mammal observations during seismic surveys in 2000
(2003)
Stone, C.J.
There were 467 sightings of marine mammals (9,258 individuals) during seismic surveys in UK waters and some adjacent areas in 2000. 12,069 hrs 40 mins were spent watching for marine mammals during seismic surveys in 2000. The most frequently seen species were white-sided and white-beaked dolphins. Sperm whales, fin whales and minke whales were also seen with moderate frequency, with lower numbers of sightings of other species. 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.

Summary

 
There were 467 sightings of marine mammals (9,258 individuals) during seismic surveys in UK waters and some adjacent areas in 2000. 12,069 hrs 40 mins were spent watching for marine mammals during seismic surveys in 2000.
 
The most frequently seen species were white-sided and white-beaked dolphins. Sperm whales, fin whales and minke whales were also seen with moderate frequency, with lower numbers of sightings of other species. 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 controlling 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 fin whales, sperm whales, white-beaked dolphins, all baleen whales combined and all dolphins combined did not differ significantly with seismic activity.
 
After controlling for weather conditions at the time of the sighting, white-beaked dolphins, white-sided dolphins and all dolphins 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 a decreased tendency for cetaceans to engage in feeding activity during periods of shooting. Positive interactions of cetaceans with the survey vessel or its equipment occurred significantly more often when the airguns were not firing. When all baleen whales, all dolphins or all cetaceans were combined, significantly fewer were found to be heading towards the vessel during periods of shooting. Similarly, significantly more dolphins were observed to be heading away from the vessel during periods of shooting.
 
Sample sizes were lower for site surveys than for surveys with larger airgun arrays. Where sample sizes were sufficient to permit statistical testing for site surveys, no effects of seismic activity on sighting rates of marine mammals or the distance they remained from the airguns were found. However, some low level disturbance was indicated on site surveys, as significantly fewer animals were observed heading towards the vessel during periods of shooting when all dolphins or all cetaceans were combined.
 
Sample sizes were low for many species, therefore the results should be treated with caution.
Both notification and a report were received by JNCC for 76% of seismic surveys taking place during 2000 (in blocks licensed in the 16th, 17th and 18th rounds of offshore licensing).
 
The use of dedicated marine mammal observers had increased slightly from previous years, but such observers were still only used on a minority of surveys. Where JNCC requested specific types of observers on surveys, these requests were complied with on 62% of occasions for the primary observer, but on only 41% of occasions for the secondary observer.
 
The duration of pre-shooting searches for marine mammals met or exceeded the required minimum of 30 minutes for 79% of occasions when the airguns were used during daylight hours in blocks where compliance with the guidelines was a licence condition (16th, 17th and 18th round blocks), which represents a decline in standards from previous years. This decline was mainly due to inadequate pre-shooting searches on site surveys, particularly where members of ships' crews were responsible for marine mammal observations.
 
Excluding site surveys, 95% of soft-starts met or exceeded the required minimum duration of 20 minutes in blocks where compliance with the guidelines was a licence condition. This represents an increase in standards from previous years.
 
For site surveys, soft-starts were mostly inadequate. Only 37% of soft-starts were of acceptable duration for site surveys in blocks where compliance with the guidelines was a licence condition.
 
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; the subsequent soft-start should also last for a minimum of 20 minutes. On all seven occasions shooting was delayed for at least 20 minutes, but on one occasion the subsequent soft-start was too short. The proportion of delay situations where correct procedures were followed had increased from previous years.
 
For surveys with large airgun arrays, the guidelines were applied throughout all UK waters, not just in those blocks (16th, 17th and 18th round) where compliance with the guidelines is a licence condition. There was little difference in the standard of pre-shooting searches and soft-starts between blocks, and there was one instance of shooting being delayed outside 16th, 17th and 18th round blocks.
 
For site surveys there was a difference in the level of compliance with the guidelines according to the location of the survey. The standard of pre-shooting searches and soft-starts was lower outside 16th, 17th and 18th round blocks.
 
The main area of concern regarding compliance with the guidelines was site surveys. Standards of pre-shooting searches and soft-starts were low, and reports from site surveys were often missing or incomplete.
 
Differences were found in the level of compliance with the guidelines according to the type of observer used. Dedicated marine mammal observers provided the highest standard of pre-shooting searches, while fishery liaison officers showed a gradual improvement in the standard of their pre-shooting searches. Members of ships' crews were the least likely to perform an adequate pre-shooting search. There was considerable variation in the standard of soft-starts on site surveys according to the type of observer used; very few soft-starts were of adequate duration when either fishery liaison officers or members of ships' crews were acting as marine mammal observers.
 
There were also variations in the quality of observations according to the type of observer used. Dedicated marine mammal observers were more efficient at detecting marine mammals than other personnel. Dedicated marine mammal observers also made fewer errors when completing the recording forms, and their identification skills were better than those of other personnel. However, fishery liaison officers had improved both their ability to detect marine mammals and their identification skills from previous years. The ability of ships' crew members to detect marine mammals was very low.
 
The use of trained, dedicated marine mammal observers is recommended, both in terms of compliance with the requirements of the guidelines and the provision of high quality data. Sole reliance on members of ships' crews to carry out observations of marine mammals is the least effective alternative.
 
A number of items for consideration when the Guidelines for minimising acoustic disturbance to marine mammals from seismic surveys are next revised are noted.
 
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89 pages
ISSN 0963 8091
 
Please cite as: Stone, C.J., (2003), Marine mammal observations during seismic surveys in 2000, JNCC Report 322, 89 pages, ISSN 0963 8091