The Davis Strait - DCE - Nationalt Center for Miljø og Energi

detailed studies on the effect of seismic surveys on bottlenose whales, pilot
whales, white beaked dolphins or harbour porpoises. White whales, narwhals
and bowhead whales are also sensitive to seismic sounds, but are present
in the area during wintertime only. Bowhead whales, for example, migrate
through part of the assessment area in December-January (Heide-
Jørgensen & Laidre 2010). The risk of overlap between these species and
seismic operations is therefore confined to winter.
In general, seals display considerable tolerance to underwater noise
(Richardson et al. 1995), confirmed by a study in Arctic Canada in which
ringed seals showed only limited avoidance of seismic operations (Lee et al.
2005). In another study, ringed seals were shown to habituate to industrial
noise (Blackwell et al. 2004). However, walruses, especially when hauled
out, may be disturbed and displaced by seismic activity but not so much by
the seismic noise. There is an important winter feeding and mating ground
for walrus where they haul out on ice directly north of the assessment area.
Mitigation of impacts from seismic noise
Mitigation measures generally recommend a soft start or ramp up of the airgun
array each time a new line is initiated (review by Compton et al. 2008).
This allows marine mammals to detect and avoid the sound source before it
reaches levels dangerous to the animals.
Secondly, it is recommended that skilled marine mammal observers are present
onboard the seismic ships in order to detect whales and instruct the
crew to delay shooting when whales are within a certain distance (usually
500 m) of the array. In sensitive areas detection of whales in the vicinity can
be made more efficient, depending on species, with the additional use of
hydrophones for recording whale vocalisations (Passive Acoustic Monitoring
– PAM); although the whales present would not necessarily emit sounds.
There are problems with respect to visual observations. In Arctic waters,
very high sound pressures may occur far from the sound source and out of
sight of the observer (see above). Another problem is that seismic surveys
are carried out day and night, and visual observations are only possible in
daylight.
A third mitigating measure is to close areas in sensitive periods. The spawning
grounds for herring and cod are closed for seismic surveys in the Lofoten-Barents
Sea area during the spawning season.
NERI (now DCE) has issued a set of guidelines for conducting seismic surveys
in Greenland waters, and protection areas (where seismic surveys are
regulated) for narwhal and walrus are designated in areas outside the present
assessment area (Boertmann et al. 2010). A similar protection area for
the bowhead whale should be considered in the Disko Bay waters in spring.
Finally, it is recommended that local authorities and hunters' organisations
be informed before seismic activities take place in their local area. This may
help hunters to take into account that animals may be disturbed and displaced
from certain areas at times when activities are taking place.
In Arctic Canada a number of mitigation measures were applied to minimise
impacts from seismic surveys on marine mammals and the subsistence hunting
of these (Miller et al. 2005). Some were identical to those mentioned
above, and the most important was a delay in the start of seismic operation
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