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After the Spill This section is a compilation of information from various sources including the Fisheries Research Services (FRS) & the Ecological Steering Group on the Oil Spill in Shetland (ESGOSS). It summarises events and research undertaken in the years after the spill and long-term impacts on the Shetland environment. |
associated with the analytical method and the restrictions placed on the number of samples that can be collected and analysed from one location, combined with the inherent sediment variability. These estimates account for a total of around 45-50% of the original cargo. The remainder was assessed as either having dispersed to concentrations approaching background levels or degraded by natural processes. Environmental and ecological impact The south Mainland of Shetland has a varied but narrow economy depending on fishing, aquaculture, shell fishing and agriculture. It is also rich in scenic and heritage values. Like most oil spills, this had damaging environmental and ecological effects. The impact of any oil spill can be measured by changes to habitats that were damaged, by mortalities of plants and animals, and by sub-lethal effects on both short and long time-scales. The Braer oil spill had several unique aspects. These were not only a product of the way the oil was mixed with the sea and the corresponding absence of oil stranding on the coast. They were also due to Shetland-specific ecological and economic circumstances. For example, there were a number of salmon farms that were affected, a circumstance which, quite apart from its serious economic and social implications, gave scientists a unique opportunity for monitoring a captive species; the amount of scientific data on prior conditions, e.g., on otters and birds was much greater than would be expected for comparable coastlines elsewhere in the UK - the dependence of the economy on fishing demanded more vigorous attention than usual from government marine laboratories; and the heritage interest, as expressed by the presence of areas with statutory designations, was considerable. |
In the early aftermath of the spill, the FRS gave priority to the monitoring of commercial fish and shellfish species and of farmed salmon. Flesh samples of these species were tasted by a panel of experts for the presence of taint and analysed chemically for oil concentration. Based on FRS' findings, a Fisheries Exclusion Zone prohibiting the taking of wild fish and shellfish and farmed salmon was quickly established to protect the public from exposure to potentially contaminated fish and shellfish. These also served to maintain the public confidence in the quality of produce from those areas of Shetland unaffected by the spill. |
Farmed salmon The contamination effects of the spill were confined to salmon farms in the south and west of Shetland. Although no direct mortalities were ascribed to the oil, caged fish were unable to swim away and so became heavily tainted and severely contaminated. Oil contamination varied from site to site, but rapid uptake took place. In the context of food safety, the predominant hydrocarbon family of concern is the polycyclic aromatic hydrocarbons (PAH). Once visible oil was no longer present, PAH levels fell rapidly reaching reference concentrations after about 150 days. Those contaminated fish close to being marketed were culled and compensation was given. Younger fish, still some twelve months from harvest, were contaminated, but by the second half of 1993, were free from taint and had typical PAH concentrations. There was also no sign that there was any resuspension of sediment that might contaminate fish in cages and the Exclusion Order for farmed salmon was lifted in December 1993. |
Wild fish Wild fish were contaminated, but at lower levels than those seen in farmed salmon, presumably because they swam away from the areas of highest pollution. The residual oil in the sea bed west and south-east of Shetland, showed no evidence of any effects on whitefish. Generally, round fish, such as cod and haddock which inhabit the water column, were less contaminated than flat fish, such as lemon sole and dab which live in close contact with the sediment. PAH levels fell rapidly to reference concentration values by the middle of March 1993 and the Exclusion Zone for these species was lifted in April 1993. For sandeels, a species of critical importance to several food chains, and an important indicator species for the contamination of sea bed sediments, there was no change in distribution around south Shetland following the spill. In areas where the sea bed was relatively strongly contaminated with oil, there was evidence of some physiological response to oil contamination, but none of effects on sandeel populations. Shellfish The degree of contamination of shellfish also varied with habitat. Crustacean shellfish such as the Norway lobster, Nephrops norvegicus, which live in and on the finer, most heavily impacted sediments, were the most severely affected. Water filtering shellfish, such as mussels, also accumulated high PAH levels. Those bivalve molluscs which favour coarser sediments, for example, scallops and queens were less severely affected. Shellfish took longer to eliminate their hydrocarbon burdens than wild fish, due to their higher initial burdens and slower rate of loss, partly due to the fact that they were in direct contact with contaminated sediment. Research showed that short term exposure to oil concentrations of 4 ppm, 10 ppm and 50 ppm has an adverse effect on adult, juvenile and larval lobsters and on lobster eggs. In the days following the spill the waters around the wreck site exhibited oil concentrations as high as 50 ppm (20,000 times 'normal' levels), but by ten days after the spill this had fallen to about 4 ppm. With the exception of Nephrops, the Exclusion Order was lifted for crustaceans at the end of September 1994. The Order was lifted for scallops and queens in February 1995. But restrictions remained in place for Nephrops and for mussels. Within the area of the Zone, Nephrops were predominantly to be found in the still heavily contaminated Burra Haaf area. Not surprisingly, levels fell most slowly here. Mussels typically showed depuration during the summer followed by slight increases during winter. This is thought to be a reflection of previously deposited contamination becoming remobilised by winter storms and available for uptake. Eventually, the Order for these species was lifted in March 2000, more than seven years after the event. The Island's fisheries were compensated for their losses. Compensation for the destruction of the 1991 and 1992 salmon stocks was respectively £7.176 and £12.118 million. The effects of the exclusion zone on the fishing fleets attracted compensation of £1.363 million for the demersal fleet and £4.57 million for the shellfish fleet. Compensation for market losses in reduced prices for Shetland seafood products was worth a further £3.781 million. However these payments do not really reflect the economic losses (or reputation) that can last for some time. Benthic Communities The benthic communities in areas of fine sediment affected by oil showed disturbances to populations but not such as to disrupt community structure significantly; there were some increases in characteristic opportunistic and oil tolerant species of macrofauna, and an abundance of some indicator meiofauna species had declined. In near-shore and inter-tidal coastal areas, there was little evidence of hydrocarbon contamination, and residual sediment toxicity was negligible. For the coastal macrobenthos, the oil does not appear to have affected communities significantly. On rocky shores, any impact was small and limited to coastlines near the wreck. Overall, the oil spill had a surprisingly light effect on near-shore and coastline habitats. Wildlife In seals, otters and cetaceans, the short-term effects of the oil spill were negligible. For all species of birds, direct mortality was low by comparison with other spills or periodic wrecks, and there were no signs of sub-lethal toxic effects (apart from some minor effects on kittiwakes). Populations of shags and black guillemots in the immediate area of the spill were reduced, but there were no effects on breeding success in these or any other species. Land On land, effects were confined to very small areas (e.g., damage to bryophytes was localised to a 10m band between Garths Wick and Garths Ness). Effects on livestock, plants, grazing land and soils were slight and short-lived. |
Gulfalks oil equivalent (µg g-1 dry weight) in surface sediment collected from Burra Haaf between 1993 and 2003. |
Longer term monitoring With the passage of time, FRS monitoring increasingly turned to the longer term fate of oil in the sedimentary basins. From 1993, core sediment samples were collected from the Burra Haaf and the south east Fair Isle sedimentary basins. The figure shows the change in Gullfaks oil equivalents (µg g-1 dry weight) in the 0-2 cm sediment cores taken from the Burra Haaf for ten years after the spill. |
The total PAH concentrations at different horizons at several stations in the Burra Haaf area in 2003 showed that levels are now lower at the surface. The low levels at greatest depth are presumed to be a reflection of the situation pre-Braer. This apparent movement of hydrocarbon contamination downcore could be the consequence of continuing deposition of relatively uncontaminated material onto previously deposited and Braer impacted horizons. The vertical axis on the graph is on a logarithmic scale. This allows a greater range of concentrations and their decline over time to be better appreciated. The figure shows that levels in surface sediments have fallen by over 100 times during the monitoring period. By 2003, total PAH concentrations in surface sediments were generally low with individual PAH concentrations below |
background concentrations. Despite this, all Burra Haaf sediments still showed evidence of past petrogenic contamination and of Gullfaks in particular, since biomarkers typical of North Sea oil could be seen. FRS has undertaken biological effects monitoring in the ten year period since the spill, measuring the levels of detoxifying enzyme produced in the liver of the dab. In 1993, enzyme levels were higher in fish taken from the sedimentary basins mentioned above. By 1996, however, and on subsequent occasions, levels had fallen to those found at remote sites. Although this was the eleventh largest spill in history, the overall environmental impact was localised and apparently less obvious than in other spills. Adverse impacts did occur but were limited due to the very light nature of the oil. Those same properties however, enabled its widespread dispersion which resulted in its incorporation into areas of fine sediments and the biota living in their vicinity. Harvesting of crustacean and bivalve shellfish from some areas was affected for several years. By early summer 1993 the only visible part of the Braer was the bow and the surrounding waters were clear. Seals now swim around the wreck, birds nest and feed nearby and the vegetation has recovered. It was estimated that Shetland would lose £18.2 million of tourist revenue by the year 2000 as a result of the oil spill (The Scotsman, 1994). In the short term, tourism was certainly reduced following the spill but today it is hard to visualise the events of January 1993 when the eleventh largest oil spill in history impacted the coastline of Shetland. |
The only part of the Braer visible at the end of 1993. There is now nothing visible. Photo, W. Ritchie. |
braer.net |
M.V. Braer grounding and oil spill Garth's Ness, Shetland, 5 Jan 1993 |
The nature of the Braer oil, a partially weathered oil with a low wax content, and the extreme weather over the period of the spill combined to disperse most of the oil into the water, often to considerable depths. Consequently, very little of the oil was found on the rocky shores, beaches or shallow subtidal sediments around Shetland. The wind at the time was so severe that a significant amount of oil was carried onshore, although its effect was minimal and it degraded quickly. The bulk of the oil was dispersed into the water column to the west of Shetland with the highest concentrations found in the immediate coastal waters and decreasing concentrations to the west. Concentrations in the water to the east and |
south of Shetland were low. The oil was transported by the prevailing currents until it reached quiescent areas, where it deposited onto the sediments. Two of these areas are offshore, one to the west of the Shetland peninsula in Burra Haaf, the other south-east of Fair Isle. Oil was also deposited in the sheltered Voes of south-west Shetland. In all around 35 % of the oil can be accounted for in these sediment sinks. The oil in these sediments is likely to be long-lived. Studies carried out in 1993 1994 and 1995 show that the oil was mixing down into the sediments but with little evidence of degradation. |
Wreck Site |
Fair Isle |
The Marine Pollution Control Unit suggested that approximately 1% of the oil (800 tonnes) was deposited on the seashore. On the basis of measurements of oil in soil or on plants, it has been estimated that perhaps as much as 600 tonnes of the oil could have been deposited on the adjacent land, affecting about 12% of the coastline of Shetland. Some of the oil was volatilised or transported by the wind away from the wreck in the direction of the land. Unfortunately, no measurements were made to permit a quantitative assessment of the amount of Braer oil lost through volatilisation. Measurement of losses from experimental slicks in the North Sea and elsewhere have indicated that within a matter of hours those components with boiling points less than 150 °C are volatilised. However, the Food Science Laboratory, Norwich, found elevated concentrations of ethyl benzenes and xylenes in salmon taken from the nearby farms shortly after the spill. These components have boiling points that range from 136 °C to 144 °C and might have been expected to volatilise. It is assumed therefore that these components were retained in the oil droplets in the water because of the rapid dispersion of the oil into the water. This information, taken together with the composition of Gullfaks crude suggests that less than 12% (approx. 10,000 tonnes) of the crude oil and perhaps 20% (360 tonnes) of the fuel oil would have evaporated. A further unknown amount of oil would have been lost through aerosol formation and atmospheric transport. All of these estimates have a large margin of error but an estimate of the quantity of oil that remained in the marine environment can be drawn from survey work carried out. These indicate that about 35 % of the oil discharged from the tanker was ultimately deposited in the sediments around Shetland. Total oil spilled 84,000 tonnes Estimated oil on coast / land <800 t (<1%) Estimated oil in subtidal sediments 30,000 t (35%) Estimated oil in atmosphere 8,000-16,000 t (14%) Although the estimates for oil in sediments are better than those for the oil deposited on land or transported in the atmosphere, they also carry a wide margin of error |
Levels of oil in water around the Shetland coast, Jan - Apr 1993. From 'Impact of an oil spill in Turbulent Waters: The Braer'. |