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

In general, species with distinct spawning concentrations and with eggs and
larvae in distinct geographic concentrations in the upper water layer will be
particularly vulnerable. The Barents Sea stock of Atlantic cod is such a species,
where eggs and larvae can be concentrated in the upper 10 m in a limited
area. Based on oil spill simulations for different scenarios and different
toxicities of the dissolved oil, individual oil exposure and population mortality
have been calculated for the Barents Sea stock of Atlantic cod. The population
impact is to a large degree dependent on whether there is a match or a
mismatch between high oil concentrations in the water column (which will
only occur for a short period when the oil is fresh) and the highest egg and
larvae concentrations (which will also only be present for weeks or a few
months, and just be concentrated in surface water in calm weather). For
combinations of unfavourable circumstances and using the PNEC with a 10
X safety factor (Johansen et al. 2003), there could be losses in the region of
5%, and in some cases up to 15%, for a blowout lasting less than two weeks,
while very long-lasting blowouts could give losses of eggs and larvae in excess
of 25%. A 20% loss in recruitment to the cod population is estimated to
cause a 15% loss in the cod spawning biomass and it would take approx.
eight years for the population to recover fully.
Hjermann et al. (2007) reviewed the impact assessment of the Barents Sea
stock of Atlantic cod, herring and capelin by Johansen et al. (2003) and suggested
improvements by emphasising the need for more focus on oceanographic
and ecological variation in the modelling. It was also emphasised
that it is not possible to draw conclusions about on long-term effects due to
the variability in the ecosystem. At best, we can attempt, by modelling, to attain
a quantitative indication of the possible outcomes of oil spills in the ecosystem
context. Qualitatively, we can assess at which places and times an oil
spill may be expected to have the most significant long-term effects.
Compared with the Lofoten Barents Sea area, there is much less knowledge
available on concentrations of eggs and larvae in West Greenland, including
the assessment area. However, the highly localised spawning areas of cod
with high concentrations of eggs and larvae for a whole stock near the surface
seen in the Lofoten-Barents Sea do not currently occur in West Greenland.
However, there have been spawning grounds of cod in West Greenland
during the past century and recolonisation by cod of the assessment area
is possible. Currently, the cod fishery in Southwest Greenland is highly
influenced by recruitment from Icelandic spawning grounds. Occasionally,
significant quantities of offspring from Iceland are transported with the
Irminger current to Greenland waters.
Eggs of Atlantic cod concentrate in the upper 10 m of the water column,
whereas larvae of shrimp and Greenland halibut are found deeper and
would therefore be less exposed to harmful oil concentrations from an oil
spill at the surface. This implies that an oil spill would most likely impact a
much smaller proportion of a season’s production of eggs and/or larvae of
these species than modelled for cod in the Barents Sea. Impacts on recruitment
to Greenland halibut and northern shrimp stocks would therefore
most likely be insignificant. However, a subsea blowout with the properties
and quantities of the Deepwater Horizon spill in 2010, when huge plumes of
dispersed oil occurred in the water column, may expose eggs and larvae
over much larger areas and depth ranges, and potentially impact the recruitment
and stock size of these bottom-living species.
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