Environmental Statement - Maersk Oil

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Balloch Field Development Environmental Statement
Section 6 Accidental Spills
vulnerable to oil during laboratory experiments. Any changes in the distribution and abundance of
plankton communities could result in secondary effects on organisms that depend on the plankton as
a food source, including commercial fish species and marine mammals. There is also the possible
accumulation and bioaccumulation up the trophic levels of pollutants ingested by plankton (SAHFOS,
2001). However, the plankton community is generally less vulnerable to one‐off incidents such as
crude oil or marine gas oil spills than continuous releases, as many species have the capacity to
recover quickly due to the continual exchange of individuals with surrounding waters (North Sea Task
Force, 1993).
As a result, in the unlikely case of a spill occurring, any immediate potential impacts to plankton
associated with the proposed drilling operations are likely to be short‐term (1 ‐ 2 years). The overall
impact on phytoplankton populations from a tier 3 spill is expected to be slight. It is recognised that
there is potential for longer term variation in populations of organisms at higher trophic levels if a
very large spill over a long period (e.g. >4 months) were to occur, which could affect the spring
plankton bloom.
6.6.2. BENTHIC COMMUNITIES
Oil has been reported to reach the seabed from blowouts (e.g. substantial water column oil
contamination has been reported following the Deepwater Horizon incident, as well as after the
Ekofisk blowout). Thus far this has been without recorded biological effect (DTI, 2001), although
future studies from the Gulf of Mexico may change this view. Investigations into the fate of oil from
the Braer grounding on Shetland in 1993 concluded that less than 1 % was carried ashore to beaches,
14 % evaporated and 85 % went into the water column; subsequently, approximately 30 % of the oil is
believed to have deposited in the seabed sediments, including an area to the southeast of Shetland
some 30 km from the release (Topping et al., 1997). The nature of the oil, partially biodegraded in the
reservoir, meant that further biodegradation rates were low and over 3 years of monitoring no
significant reduction in the deposited oil concentrations was observed, although there was some
redistribution of the oil vertically downwards into the sediment. Some decline in polycyclic aromatic
hydrocarbons (PAHs) , some of the more harmful components, was observed over this period, but this
was not observed at all locations.
Therefore, in the unlikely case of a very large spill occurring from the proposed operations, it is
recognised that there is potential for moderate/severe benthic impacts. Sediments could potentially
become locally contaminated with high levels of hydrocarbons for long periods of time, which in turn
could cause toxic impacts to the benthic communities.
6.6.3. FISH
Several fish species have been recorded across the North Sea; annual fish landings data presented to
ICES include over 200 species of fish and shellfish. Some of the more commercially important species
known to spawn in the area of the development are given in Table 3‐12.
It is likely that fishing would be suspended in the vicinity of a release until monitoring could be carried
out, reflecting the fact that oil in water concentrations very close to the release point could be toxic
to fish and cause tainting. Modelling predicts that water column oil and surface oil will disperse,
degrade and evaporate within days and weeks of the release ceasing.
Fish are not generally affected by oil slicks on the sea surface and mature fish of most species can
tolerate water‐soluble oil fraction concentrations of about 10 mg/l. Some species can survive much
higher concentrations unless whole oil or dispersed oil droplets coat the gills and cause asphyxiation.
Adult fish are generally more resistant than other marine organisms to oil because their surfaces are
coated with an oil‐repellent mucus, but they can be affected through the gills, by ingestion, or by
eating oiled prey (USCG, 2006). Although various developmental disorders may occur to some degree
under oil slicks, as well as mortalities, so far it has proved impossible to detect consequential effects
on adult populations. Potential sub‐lethal effects of spilled oil on fish include impairment of
reproductive processes and increased susceptibility to disease and predators. In fish life cycles, it is