SEEEC Report Summary
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1. Setting the Scene
On 15 February 1996 the Sea Empress, bringing crude oil to Milford Haven in south-west Wales, ran aground and over the following week released 72,000 tonnes of crude oil and 480 tonnes of fuel oil into the sea. Despite a rapid and effective clean-up response at sea, oil came ashore along 200 km of coastline – much of it in a National Park – in an area of international importance for its wildlife and natural beauty. A ban was imposed on commercial and recreational fishing in the region and there was concern that tourism, important to the local economy, would be badly affected by the heavily oiled beaches. Several thousand oiled birds washed ashore, leading to a major cleaning and rehabilitation operation.
This is a summary of the report on the spill prepared by the Sea Empress Environmental Evaluation Committee (SEEEC), an independent committee set up on 27 March 1996 by the UK Government with the terms of reference given below (Box 1).
The committee’s full report describes the impact the oil has had on the environment, both at sea and along the shore. It looks at the response to the spill – the clean-up operation, the environmental monitoring programme and the cleaning of oiled birds – and recommends changes in the arrangements for assessing and responding to future spills.
Over a period of 20 months, SEEEC brought together teams of experts and commissioned about 80 scientific studies involving government and public bodies, universities, voluntary organisations, research institutes and companies specialising in oil spill and ecological assessment. The results of these studies along with earlier research on the ecology of the area – and work carried out by other organisations – provided information for this report.
Box 1 SEEEC's terms of reference:
- To co-ordinate monitoring work carried out by government departments and other public bodies to assess the environmental impact of the Sea Empress oil spill and the subsequent clean-up activities.
- To ensure that a comprehensive set of monitoring data on environmental distributions and impacts is obtained, taking account of studies by other organisations and the need to avoid gaps and overlaps.
- Through these monitoring programmes, to assess the overall impact of the incident on environmental resources of the area affected, these resources to include fisheries, agriculture, amenity and wildlife conservation, and to assess the subsequent recovery of these resources. Information on the distribution of pollutants relevant to human health will be passed to public health authorities for assessment.
- To publish the principal findings and conclusions of these studies with the purpose of informing the Government, the public and those specific groups directly affected by the incident. Recommendations will be made where improvements in procedures or further actions are required, which might have wider application.
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The accident itself and the salvage operation were investigated by the Marine Accident Investigation Branch of the Department of the Environment, Transport and the Regions (DETR) which published its report in July 1997. The Marine Pollution Control Unit (MPCU) produced a detailed account of the clean-up operation. Soon after the spill, Pembrokeshire County Council, supported by other public bodies, commissioned a study of its potential economic consequences. The effects of the spill on public health are being investigated by the Dyfed Powys Health authority and a report has been published.
Environmental monitoring work to assess the initial impact started soon after the grounding of the tanker, and SEEEC supplemented this work with a programme of longer-term studies. It was clearly impossible to cover every aspect of the ecology of the region, but all the main types of onshore and marine environments were included in the programme, focusing on key species that were:
- heavily impacted by the oil,
- indicative of the health of the environment,
- of conservation importance to the area,
- important in the marine food chain, or
- of economic value.
The eventual programme of projects proposed by SEEEC – costing about Ł2 million – was funded by the government and its agencies with support from local authorities, the European Commission (EC), voluntary organisations and industry.
South-west Wales is an area of great natural beauty and ecological interest. Around three quarters of the shoreline is made up of rocky cliffs, rock platforms, boulders and shingle, with most of the rest being mud and sand habitats, including some sandy beaches of high amenity value. In recognition of the region’s environmental importance, many areas have been given special national or international status. Much of the coastline lies within the Pembrokeshire Coast National Park, and in the main area affected by the spill there are about 35 Sites of Special Scientific Interest, 2 National Nature Reserves (at Stackpole and Skomer) and, around Skomer, one of the UK’s three Marine Nature Reserves. There are also EC designated Special Protection Areas for birds, and
plans for three Special Areas of Conservation are proposed by the government.
The main towns in south-west Wales are Carmarthen (population 14,600), Milford Haven (13,600), Haverfordwest (13,000), Pembroke Dock (8,600) and Pembroke (7,200). The local economy faces problems from the closure of major industrial and defence establishments and from the decline of the oil-processing and agricultural sectors. Unemployment rates in Pembrokeshire are amongst the highest in Wales. The region’s economy relies heavily on a few key industries, particularly oil, tourism, agriculture and fishing.
Tourism plays a vital role, with many visitors staying in the vicinity of Tenby and Saundersfoot. Opportunities for environmental education are offered by field studies centres. In 1995 tourists spent an estimated Ł160 million in Pembrokeshire.
The fishing industry is centred around the Milford Haven waterway. The region has abundant shellfish, crabs, lobsters, sea bass and other fish, and the local salmon and sea-trout rivers attract many visiting anglers.
These fisheries provide an estimated 1,000 land- and sea-based jobs. Agriculture in the region includes early potatoes and vegetables,
dairy and livestock farming.
The Milford Haven waterway has a long history as an oil port, developed during the 1950s for its deep waters and natural shelter – features making it ideal for large tankers. Whilst it is the second busiest port in Britain for petroleum products, high transport costs from Pembrokeshire have lead to the oil refineries becoming less competitive in recent years.
2. Fate of the Oil
Over a period of seven days – while the Sea Empress was grounded outside the entrance to Milford Haven waterway – about 72,000 tonnes of light crude oil was released, mainly at low tide. About 250 tonnes of heavy fuel oil (used to power the ship’s engine) was also released at this time and probably mixed with the crude oil; a further 230 tonnes was released after the tanker had been towed to a jetty within the waterway.
While the tanker was grounded, the wind varied between a moderate breeze and a near gale and initially (15-17 February) the released oil was driven towards the Haven. From 18 to 22 February (a period during which about 90% of oil was released) the winds carried the oil south, away from the Pembrokeshire shoreline, allowing chemical dispersants to be used to disperse the oil into deep water. On 23 February the wind veered to the south-west and over the next few days carried residual oil to the beaches of Carmarthen Bay, mainly from Tenby to Pendine.
Crude oil is a mixture of a very large number of different components. Tests at the spill showed that about 40% of the oil – including many of the components that are toxic to marine life – evaporated rapidly after release. For much of this period the winds were offshore. Oil vapour concentrations were measured continuously on shore, though these remained low, reaching a maximum of 9 parts per million (ppm). (It had been agreed that action, for example advising people to stay indoors, would be taken if concentrations rose above 50 ppm) A predictive model confirmed that concentrations of oil vapour over land would be low because of the generally favourable wind directions.
About 50% of the oil dispersed in the water column, due to natural mixing and the use of 446 tonnes of chemical dispersants sprayed onto the oil from aircraft. The dispersants enhanced the effectiveness of natural processes in causing the oil to form small droplets and mix into the water, substantially decreasing the amount of oil on the surface but increasing concentrations at depth. Oil remaining on the sea surface generally formed an emulsion (a stable mixture of about 70% water and 30% oil) which impeded the natural dispersion process, though monitoring from boats in the area where the dispersant was being sprayed confirmed the effectiveness of the chemical dispersants even on emulsion. In addition to the dispersant operation, around 1-2% of the oil was
collected from the sea surface using recovery vessels.
Oil is a natural product and eventually most of it will have been broken down by micro-organisms in the water. By the end of March concentrations of oil in the water column were low (less than 100 µg/l) and near to background levels over the affected area.
Extensive offshore surveys were conducted to determine if oil had combined with sediment particles and been deposited on the sea bed. No major concentrations of oil were found, except near to some shores where bulk oil had remained for long periods.
Oil came ashore along 200 km of coastline, with the worst hit areas within the Milford Haven waterway and along the south Pembrokeshire coast. Estimates suggested that between 3,700 and 5,300 tonnes of oil came ashore (5-7% of the total); this was reduced to about 500 tonnes by late summer as a result of a major shoreline clean-up operation and natural cleaning. Much of the oil remaining by the end of summer was buried below the surface.
3. Marine Impacts
As a precautionary measure, a ban on all fishing and the collection of edible plants and seaweeds was imposed shortly after the spill for an area stretching from St David’s Head to Port Eynon on the Gower (see map). Fishing for salmon and sea trout was also banned in the rivers flowing into this area. Samples of various species of fish, shellfish and crustaceans were analysed for oil content over the subsequent months, and the closure orders were lifted in stages as analysis showed that oil concentrations in different classes of organism had returned to background levels. Salmon and sea trout did not appear to have been affected and the ban on these was lifted on 3 May 1996, while that for other fish was lifted on 21 May 1996. The ban was lifted for crabs and lobsters outside the Milford Haven waterway and for whelks throughout the whole area on 29 August 1996, and over the following year the ban was progressively lifted in stages until all remaining restrictions were removed on 12 September 1997.
Whilst there was no clear evidence of damage to commercial stocks of fish, extended monitoring – particularly of individuals reaching commercially-exploitable size – will be required to determine whether breeding and recruitment of some species (including bass, edible crabs, lobsters and whelks) was successful after the spill in 1996.
The catch rate in the Tywi of sea trout – though not of salmon – decreased in 1996, but further analysis of catch data from other rivers is required before this decrease can be attributed to the spill.
In the weeks following the spill large numbers of dead or moribund animals were washed ashore – mostly bivalve molluscs (such as cockles and razor shells) and sediment-dwelling animals of the lower shore and below the shoreline. This phenomenon can happen naturally with some species, but the timing, number of individuals, range of species and in some cases increased levels of tissue hydrocarbons suggested that most of the strandings were related to exposure to the oil. Studies of the seabed showed little impact resulting from the spill except for the absence of amphipods (small crustaceans which are important in the food chain) in some areas near to the site of the spill. The death of amphipods and the stranding of molluscs have both been recorded following other major oil spills. The use of dispersants, in distributing oil droplets deep into the water column, may have increased the exposure to oil of those species living in sediments and contributed to the strandings and the decrease in amphipod populations in some areas.
4. Shoreline Impacts
Large numbers of limpets were killed on heavily-oiled rocky shores near to the grounding site, with 90% mortality recorded in some parts of West Angle Bay. Topshells and periwinkles also died, though in lower numbers. As a result of reduced grazing by these animals, there was an extensive growth of algae (mostly green algae) which prevented the settlement of barnacle larvae at some sites. The recovery process of limpet and other mollusc populations has started but, from experience with previous spills, complete recovery is likely to take several years at the worst-affected sites.
Amphipod mortalities were extensive but substantial recolonisation was evident at most sites by 1997. Great concern was expressed about the impact on the rare cushion star (Asterina phylactica) at West Angle Bay as this population is of considerable conservation importance. Despite mortalities which reduced the populations to a very low number, a slow recovery is now under way. There did not appear to be any other serious impact on rocky shore or rock pool communities.
Impacts on sedimentary shores are generally less easy to discern as most animals are hidden, but strandings of several bivalve species were evident after the spill and amphipod populations were affected. Some opportunistic species such as polychaete worms exploited vacant ecological niches and temporarily increased in numbers, but there was evidence of a restoration of the former balance by the late autumn of 1996.
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