Environmental Report 1999 Index

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Seismic Surveys Seismic surveying techniques underpin all exploration and production. By allowing scientists to build up images of rock formations below the seabed, they help to pin-point potential oil reserves. In general terms, seismic surveying equipment uses the same principle as radar or sonar devices. Pulses of low frequency sound are released at regular intervals, then pass through the water and the seabed to be reflected by the geological layers beneath the surface of the earth. The reflected echoes are recorded and analysed, and the results are used to create a computer-generated image of the geology far below the bottom of the sea. Survey engineers use an array of underwater 'air guns' which are towed behind the survey ship and release a brief "pop" of compressed air approximately every ten seconds. The echoes coming back from the subsurface rock formations are detected by another towed-array of cables fitted with hydrophone sound detectors. During a survey, the vessel will sail along a pre-determined line several kilometres long. Seismic And Marine Mammals Industry operators fully accept that seismic survey activities should not harm marine wildlife, and all seismic surveys in UK waters are undertaken in accordance with guidelines drawn up by the JNCC after extensive consultation with the industry, NGOs and others. Guidelines aimed at minimising acoustic disturbance to marine mammals from seismic surveys and other operations where acoustic energy is released have been drawn up. The guidelines apply to all marine mammals, including seals, whales, dolphins and porpoises and UKOOA member companies and their seismic contractors comply with the guidelines in all areas of the UK Continental Shelf. The guidelines cover the planning stage, the steps to be taken during the seismic survey and the report to be made to JNCC once the survey is over. Although oil companies have been exploring the Atlantic Margin for more than 20 years, increased levels of activity in recent years have led to concerns among regulators, NGOs and the general public about the potential impact of these operations, and seismic activity in particular, on the area's marine mammals. Responding to this concern, representatives from offshore oil companies, geophysical contractors, environmental regulators and NGOs, along with marine biologists, academics and bio-acoustics specialists, met in London in June 1998 to discuss the impact of seismic operations on marine mammals. The Seismic and Marine Mammals Workshop was organised jointly by the Atlantic Margin Joint Industry Group, the International Association of Geophysical Contractors, the JNCC, the National Environment Research Council Sea Mammal Research Unit and the International Fund for Animal Welfare. The event, which attracted almost 100 delegates from across Europe and as far afield as the Far East and the United States, was the first time experts in all the relevant fields had gathered in the UK. Its purpose was to develop a common understanding of the interaction between seismic operations and marine mammals. Seismic And Fish Seismic surveys may have two potential impacts on fish - direct physical and/or behavioural effects. Physiological effects will mainly affect fish at the egg, larval and fry stages because at those times they either lack or have very limited ability to move from the area of the survey. However, research shows that the numbers affected are small, since serious injury occurs only if the eggs, larvae or fry are very close to an air gun. However, research shows that our industries' impact on the larvae and fry are insignificant. The behavioural effects on adult fish are considered to be more important. Fish vary greatly in their ability to hear sounds. In many cases, fish with good hearing (e.g., herring) have a swim bladder connected directly to the inner ear, which makes them more sensitive to sound. Due to the variation in hearing ability among fish, it is impossible to generalise about their ability to detect sounds at a particular frequency or level. Nevertheless, it is clear that many species can hear low frequency sound pulses such as those produced by seismic air guns. Evidence seems to indicate that during seismic surveys in the open sea, fish generally swim away from air guns by diving or changing direction. They are disturbed and leave the area, implying a potential knock-on effect on birds, cetaceans and seals which prey on the fish. Another consequence would be that fishing vessels in the immediate area would have reduced catches - but fishermen nearby may benefit if the shoals move into their area. Fish And Seismic Research In the summer of 1998, scientists from the Fisheries Research Services Marine Laboratory combined a tagging programme with observations of fish in the vicinity of an air gun as it was discharged. Using underwater TV cameras to monitor the behaviour of fish around an inshore reef, the researchers found that the fish displayed a brief, voluntary reaction (similar, in neurological terms, to the blink of a human eye-lid). The response was no more than would be observed if someone tapped on the glass of an aquarium window, and the moment the stimulus ceased the fish resumed their activities, with their intended track apparently unaltered. The long-term, day-to-night movements of shoals were also uninterrupted by low-frequency pulses projected into their path. This contrasts both with the reported behaviour of fish in the open sea and with the response of the inshore fish to a grey seal. Proximity to this predator produced an identifiable, disturbed pattern of behaviour that lasted for about an hour. Fisheries Sensitivities Atlas During 1998, the fisheries agencies MAFF and the Scottish Executive with support from UKOOA, the Scottish Fisherman's Federation and the National Federation of Fisherman's Organisations, prepared an atlas of fish congregation and breeding grounds. It has two purposes. First, it provides information that enables all interested parties better to understand the potential for interaction between the fishing and offshore oil and gas industries. Second, it encourages meaningful dialogue between users of the sea so that competing concerns can be addressed and, wherever possible, dealt with as early as possible. It will also aid the environmental impact assessment process; inform seismic, exploration, field development and decommissioning activities; and help in the preparation of oil spill response strategies.