1. Recording of cetaceans during 1997 operations in UK waters
and some adjacent areas, in compliance with the Guidelines for
minimising acoustic disturbance to small cetaceans, yielded a total
of 730 sightings comprising 8,528 individuals.
2. The most frequently seen species were pilot whales, fin
whales, sperm whales, white-sided dolphins, common dolphins,
white-beaked dolphins and minke whales. Sightings peaked during
July and August and were particularly concentrated in deep waters
to the north-west of the UK.
3. After taking account of various factors such as
geographical distribution, seasonal variations in sightings,
weather conditions and the power output of the airguns, the
sighting rate of pilot whales was found to be significantly higher
while the airguns were firing during seismic surveys, while
white-sided dolphins, white-beaked dolphins and all dolphin species
combined were seen significantly less often during periods of
shooting. Sighting rates of fin whales, fin/ sei whales, sperm
whales and all large whales combined did not differ significantly
between periods of shooting and not shooting.
4. Allowing for weather conditions at the time of sighting,
white-sided dolphins, unidentified dolphins, minke whales and fin/
sei whales were found to be significantly further from the airguns
when they were firing during seismic surveys than when they were
not. Most other species were also further from the airguns during
periods of shooting, but not significantly so. Although white-sided
dolphins remained further from the airguns during periods of
shooting, they were less far away if they were in association with
pilot whales than if they were on their own.
5. There were some behavioural responses to seismic activity.
Pilot whales and fin whales were more likely to swim at an
increased speed during periods of shooting. Cetaceans altered
course more often when the airguns were firing than when they were
not firing. A significantly greater number of pods of pilot whales
were seen to be heading away from the ship when the airguns were
firing. Sperm whales dived more often during periods of shooting.
Positive interactions of cetaceans with the survey vessel
(bow-riding, swimming alongside the paravanes, following the vessel
or approaching the vessel) were more frequent when the airguns were
not firing, although some individuals were sufficiently tolerant of
seismic activity to engage in positive interactions with the vessel
while the airguns were firing.
6. There were indications that in deeper water the effects of
seismic activity may be reduced. Relatively more cetaceans were
seen during periods of shooting in deeper waters than during these
periods in shallower waters.
7. Sample sizes from site surveys (small scale localised
surveys, usually made prior to drilling) were small, therefore
results from these surveys should be treated with particular
caution. There were indications from site surveys that sighting
rates of dolphins were higher when the airguns were not firing,
while sighting rates of pilot whales and unidentified large whales
were higher when the airguns were firing. However, sample sizes
were too small to test the statistical significance of these
results. No significant differences were found in the distance of
cetaceans from the airguns between periods of shooting and not
shooting.
8. The results presented here confirm many of the findings of
previous analyses of data collected during seismic surveys. The
only exception is that pilot whales have on some occasions
previously been seen less frequently during periods of shooting,
whereas in the present study the opposite situation was
found.
9. Recommendations are made for minor revisions to the
existing recording forms, and an additional form is
proposed.