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

Impact of seismic noise on zoo- and ichtyoplankton
Zooplankton and fish larvae and eggs (=ichtyoplankton) cannot avoid the
pressure wave from the airguns and can be killed within a distance of less
than 2 m, and sublethal injuries may occur within 5 m (Østby et al. 2003).
The relative volume of water affected is very small and population effects, if
any, are considered to be very limited in e.g. Norwegian and Canadian assessments
(Anon 2003a). However, in Norway, specific spawning areas in
certain periods of the year may have very high densities of fish larvae in the
uppermost water layers, and the Lofoten-Barents Sea area is closed for seismic
activities during the cod and herring spawning period in May–June
(Anon 2003a). It was concluded in an assessment of seismic activities in the
Disko West Area that it was most likely that impacts of seismic activity (3D)
were negligible on the recruitment to fish stocks in West Greenland waters
(Mosbech et al. 2007). In general densities of fish eggs and larvae are low in
the upper 10 m and most fish species spawn in a dispersed manner in winter
or spring, with little or no temporal overlap with seismic activities. Recent
studies suggest that eggs and larvae drift slowly though the assessment area
at depths of 13-40 m (Simonsen et al. 2006). There is limited data on fish egg
and larvae densities as well as zooplankton, but it can be assumed that the
density in the upper 10 m will not be significantly higher than that which
has been found to date in Greenland waters. It is therefore most likely that
impacts of seismic activity (even 3D) on zooplankton and on the recruitment
to fish stocks are negligible in the assessment area.
Impact of seismic noise on fisheries
Norwegian studies (Engås et al. 1996) have shown that 3D seismic surveys (a
shot fired every 10 seconds and 125 m between 36 lines 10 nm long) reduced
catches of Atlantic cod (Gadus morhua) and haddock (Melanogramma aeglefinus)
at 250–280 m in depth. This occurred not only in the shooting area but
as far as 18 nautical miles away. The catches did not return to normal levels
within 5 days after shooting (when the experiment was terminated), but it
was assumed that the effect was short term and catches would return to
normal after the studies. The effect was, moreover, more pronounced for
large fish compared with smaller fish.
The commercial fisheries which will overlap in space with seismic surveys in
the assessment area are the offshore trawling for Greenland halibut and
northern shrimp and snow crab catches.
A Canadian review (DFO 2004) concluded that the ecological effect of seismic
surveys on fish is low and that changes in catchability probably are species
dependent. A Norwegian review (Dalen et al. 2008) concluded that the
results of Engås et al. (1996) described above cannot be applied to other fish
species and to fisheries at other water depths. Greenland halibut is very different
from Atlantic cod and haddock with respect to anatomy, taxonomy
and ecology. For example Greenland halibut has no swim bladder, which
means that its hearing ability is reduced compared with fish with a swim
bladder, in particular at higher frequencies, as it is likely to be sensitive to
only the particle motion part of the sound field, not the pressure field.
Moreover, the fishery takes place in much deeper waters than in the Norwegian
experiments with haddock and Atlantic cod. The only study including
Greenland halibut is a Norwegian study dealing with gillnet and longline
fisheries (Løkkeborg et al. 2010). However, this study showed contradictory
results, where gillnet catches increased during seismic shooting and re-
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