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

type or timing of vocalisations. In addition, there may be indirect effects associated
with altered prey availability (Gordon et al. 2003).
There is strong evidence for behavioural effects on marine mammals from
seismic surveys (Compton et al. 2008). Mortality has not been documented,
but there is a potential for physical damage, primarily auditory damage.
Under experimental conditions temporary elevations in hearing threshold
(TTS) have been observed (Richardson et al. 1995, Anon 2005). In the USA a
sound pressure level of 180 dB re 1µPA) (rms) or higher is believed to provoke
TTS or PTS and is adopted by the US National Marine Fisheries Service
as a mitigation standard to protect whales (NMFS 2003, Miller et al. 2005).
Displacement is a behavioural response, and there are many documented
cases of displacement from feeding grounds or migratory routes of marine
mammals exposed to seismic sounds. The extent of displacement varies between
species and also between individuals within the same species. For example,
a study in Australia showed that migrating humpback whales generally
avoided seismic sound sources at distances of 4-8 km but occasionally
came closer. In the Beaufort Sea autumn-migrating bowhead whales avoid
areas where the noise from exploratory drilling and seismic surveys exceeds
117–135 dB and they may avoid the seismic source by distances of up to 35
km (Reeves et al. 1984, Richardson et al. 1986, Ljungblad et al. 1988, Brewer
et al. 1993, Hall et al. 1994, NMFS 2002, Gordon et al. 2003); although a Canadian
study showed somewhat shorter distances (Lee et al. 2005). White
whales avoided seismic operations in Arctic Canada by 10-20 km (Lee et al.
2005). Stone & Tasker (2006) showed a significant reduction in marine
mammal sightings during seismic surveys in the UK during periods of
shooting compared with non-shooting periods. In the Mediterranean, bearings
of singing fin whales estimated with passive acoustic monitoring indicated
that whales moved away from the airgun source and out of the area
for a time period that extended well beyond the duration of the airgun activity
(Castellote et al. 2010). In contrast, minke whales have been observed as
close as 100 m to operating airgun arrays (AU unpublished), which is potentially
close enough to sustain physical damage.
The ecological significance of displacement effects is generally unknown. If
alternative areas are available the impact probably will be low and the temporary
character of seismic surveys will allow displaced animals to return
after the surveys.
In West Greenland waters satellite-tracked humpback whales utilised extensive
areas and moved between widely spaced feeding grounds, presumably
searching for their preferred prey (krill, sandeel and capelin) as prey availability
shifted through the season (Heide-Jørgensen & Laidre 2007). The ability
of humpback whales to find prey in different locations may suggest that
they would have access to alternative foraging areas if they were displaced
from one area by a seismic activity. However, even though many areas can
be used, a few key zones seem to be especially important. The satellitetracked
humpback whales favoured a zone on the shelf within the assessment
area with high concentrations of sandeel (Heide-Jørgensen & Laidre
2007). Similarly, a modelling study based on cetacean and prey surveys
showed that rorquals (fin, sei, blue, minke and humpback whale) and krill
aggregate in three high density areas on the West Greenland banks (Laidre
et al. 2010). One of these important feeding areas covers the northern part of
the assessment area. Displacement from major feeding areas can therefore
189