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

Table 11.2.1. Overview of potential impacts of a large oil spill on VECs in the Davis Strait assessment area. See section 4.9 for
a summary of the VECs. This assessment assumes the application of current (2011) mitigation guidelines, see text for details.
VEC Typical vulnerable organisms
210
Population impact* - worst case
Displacement Sublethal effect Direct mortality
Pelagic hotspots halibut larvae - moderate (L) moderate (R)
Tidal/subtidal zone capelin, bivalves long term (L) major (L) major (L)
sandeel, Gl. halibut, shrimp, shelf
Demersal fish & offshore benthos short term (L)
bank benthos
moderate (L) moderate (L)
Seabirds (breeding) auks, c. eiders short term (L) major (R) major (R)
Seabirds (non-breeding) auks, eiders, harlequins short term (L) major (R) major (R)
Marine mammals (summer) baleen- & toothed whales short term (L) moderate (R) minor (R)
bowheads, hooded seals,
Marine mammals (winter)
walruses, narwhals
* L = local, R = regional and G = global
short term (L) moderate (R) moderate (R)
11.2.1 Oil spill impact on plankton and fish incl. larvae of fish and
crustacean
Adult fish and shrimp
In the open sea, an oil spill at the surface will usually not result in oil concentrations
that are lethal to adult fish, due to dispersion and dilution. Furthermore,
many fish can detect oil and will attempt to avoid it, and therefore
populations of adult fish in the open sea are not likely to be significantly affected
by an oil spill. The situation is different in coastal areas, where high
and toxic oil concentrations can build up in sheltered bays and fjords resulting
in high fish mortality (see below).
Adult shrimps live on and near the bottom in relatively deep waters (100-
600 m), where oil concentrations from a surface spill will be very low, if detectable
at all. No effects were seen on the shrimp stocks (same species as in
Greenland) in Prince William Sound in Alaska after the large oil spill from
Exxon Valdez in 1989 (Armstrong et al. 1995). Under certain conditions, a
subsea blowout may cause high concentrations of oil and dispersants in the
water column, as observed during the Deepwater Horizon spill in 2010
(Thibodeaux et al. 2011). Shrimp habitats can therefore be affected.
Fish and crustacean larvae
Eggs and larvae of fish and shrimp are more sensitive to oil than adults.
Theoretically, impacts on fish and crustacean larvae may be significant and
reduce the annual recruitment strength with some effect on subsequent
populations and fisheries for a number of years. However, such effects are
extremely difficult to identify/filter out from natural variability and they
have never been documented after spills.
The distribution of fish eggs and early larval stages in the water column is
governed by density, currents and turbulence. In the Barents Sea the pelagic
eggs of cod will rise and be distributed in the upper part of the water column.
As oil is also buoyant, the highest exposure of eggs will be under calm
conditions while high energy wind and wave conditions will mix eggs and
oil deeper into the water column, where both are diluted and the exposure
limited. As larvae grow older their ability to move around becomes increasingly
important for their depth distribution.