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Petroleum exploration at sea:
Seismic studies expose fish to "rock concert"
Petroleum exploration entails activities that affect marine life and fishery catches. How, for example, do fish react when subjected to the noise of seismic surveying at sea? Seismic "shooting" has been described as the equivalent of a continuously pounding rock concert for several weeks.
Seismic surveying is a method of using sound waves to map geological structures beneath the seabed. A technology showing rapid advancement, it is applied to petroleum exploration and other fields.
Colossal echo sounder: Seismic vessels tow a fanned array of high-pressure pneumatic guns several kilometres behind them to map oil and gas reservoirs and other geological structures. Illustration of a 3D seismic survey, where P = pressure waves and S = shear waves. (Illustration: StatoilHydro)
Seismic shooting was once performed with explosives, but today's seismic vessels employ high-pressure airguns. These specialised vessels tow a fanned-out array of kilometres-long streamers equipped with hydrophones. The system acts in principle as a gigantic echo sounder. The major difference lies in what is being mapped: oil, gas and other geological structures beneath the ocean floor.
Controversial practice in Norway
The activity produces extreme noise - as well as controversy. Norwegians experienced the shooting for four weeks this summer when seismic data collection commenced off the coast of Vesterålen in Nordland county in the start-up of surveying in connection with petroleum exploration and possible drilling for oil and gas there and near the Lofoten Islands.
The Lofoten landscape.
These areas boast spectacular natural beauty - and the shooting proved to be this summer's political hot potato in Norway. The Norwegian Storting commissioned the Institute of Marine Research to monitor the surveying activity closely and document its impact on the area's fish and other marine life.
Animal life affected
Egil Ona of the Institute of Marine Research directed the research voyages in Lofoten and Vesterålen this summer. (Photo: Kjartan Mæstad)
This summer's air-pressure salvos off Vesterålen were clearly audible, fired every ten seconds for weeks at a time. Exposure to the shooting has been likened to being forced to attend a non-stop rock concert for several weeks. Researchers know that fish and whales can hear seismic shots over 100 kilometres away.
But the body of knowledge about the effects of seismic shooting is limited. A smaller-scale study on the Nordkapp Bank in the 1990s showed that the volume of fish caught was halved from seismic surveying activities. Other research on fry and larvae conducted at Austevoll Aquaculture Research Station revealed that damage to fish larvae was considerably less severe than expected.
Fish talk too
Sound is a critical mode of communication for marine mammals and many piscine species. Through sounds, marine animals "talk" with one another about food, survival and reproduction. The low-frequency sound blasts from seismic guns invade the frequency range fish use to communicate and hear their surroundings.
This autumn the findings of the Institute of Marine Research study will reveal just how disruptive seismic shooting actually is in scaring away fish - and reducing fishery catches.
Many answers forthcoming
The summer's research project is one of the world's most comprehensive studies on how seismic data collection affects marine life and fishery catches.
The Institute of Marine Research's Egil Ona, who directed the research voyages, is extremely pleased with the quality of data he and his colleagues collected. Their specific findings, which provide many answers to how the animals react to seismic shooting, will be made public in the institute's reports to the Norwegian Petroleum Directorate and the Ministry of Fisheries and Coastal Affairs later this autumn.
| This article was originally published in Norwegian in Forskning magazine no. 3/09. Read more articles in English from this issue. |
- Published:
- 22.09.2009
- Last updated:
- 23.09.2009
