Seismic surveys both increased and reduced fish catches

These are the main results from the research commissioned by the Norwegian Petroleum Directorate (NPD) and carried out by the Institute of Marine Research during the summer of 2009 on the effects of seismic surveys off Vesterålen.

Sound waves from seismic data acquisition resulted in increased catches for some species and smaller catches for others. It appears that pollack may, to some extent, have withdrawn from the area, while other species seem to remain.

This consequential research project  is one of the largest ever conducted. The survey clearly indicates that the fish reacted to the sound from the seismic guns. The most probable explanation for both the increased and reduced catches for the various species and fishing gear is that the sound waves from the seismic guns put the fish under some stress, causing more swimming activity.  This would, for example, explain why more Greenland halibut went into the net, while long line catches of the same species declined.

NOK 25 million

The NPD both initiated and funded this research project, which had a cost ceiling of NOK 25 million. 

The seismic data acquisition was carried out in a defined section (approx. 15 x 85 km) of the area outside Vesterålen known as Nordland VII. Here the vessel ”Geo Pacific" acquired 3D seismics from 29 June to 6 August 2009.  The period was chosen based on advice from the Directorate of Fisheries, the Institute of Marine Research and the fishermen's organisations in Nordland and Troms, with the aim of conducting the survey during a period when the seismic acquisition activity would cause as little inconvenience as possible to the fishing industry, and to avoid the spawning periods.

Researching the consequences

The Institute of Marine Research was charged with the task of examining the consequences of seismic data acquisition on the presence of the fish species normally caught in this area.

The results are presented in the report entitled ”The effects of seismic surveys on fish distribution and catch rates for net and line fishing in Vesterålen in the summer of 2009".

The Institute of Marine Research commenced its studies 12 days prior to the start-up of the seismic data acquisition and continued for 25 days after the activities stopped. Chartered fishing vessels conducted fishing in the area using both nets and lines, while the research vessel "Håkon Mosby" worked with another chartered fishing vessel to map the occurrence of fish and plankton using echo sounders and sonar. In addition, stomach specimens were taken from the catches, and recordings were made of the sound from the air guns on the seismic vessel.

Results

Research on the consequences of the seismic acquisition activity identified the following:

• The net catches of Greenland halibut and Norway haddock were higher during and after the seismics than before.
• The line catches of Greenland halibut declined during the seismics, but increased afterwards.
• The catches of pollack showed a declining trend during and after the seismics, but the variations were not statistically certain.
• By-catches of ling in haddock and pollack nets showed an increasing trend immediately after the seismics started, but declined after a few days. After the seismics, the catches returned to approximately the same level as before.
• Line catches of haddock showed a downward trend towards the end of the seismic shooting when the seismic vessel approached the haddock lines. At its closest, the seismic acquisition vessel was within 1 nautical mile of the haddock lines.

Substantiates and deviates

To a large degree, the mapping using echo sounders and sonar substantiates the results from the fishing tests. Analyses of the stomach contents in the fish caught did not reveal changes which could be attributed to the seismic survey. Neither were any changes in the distribution of plankton proven during the seismic data acquisition.

The results from this study deviate from the results of previous studies, which have demonstrated considerable reductions in the catch rates for trawl and line fishing. In the previous study from the Nordkapp bank, the seismic acquisition activity was, however, concentrated within a smaller area. This entailed a stronger and more continuous sound impact on the fish (number of air gun shots per surface measure and time unit) than what was the case within the seismic acquisition area for this study.