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Seismikk_Nordland_VII6576.jpg
Seismikkfartøyet "Geo Pacific" utenfor Vesterålen sommeren 2009
Photo: Kjartan Mæstad
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Seismic activity both increased and reduced fish catches

The sound produced by a seismic survey increased catches for some species and reduced them for others. It appears that saithe may have partially migrated out of the area, whilst other species apparently stayed. These are the main findings of the Institute of Marine Research's summer 2009 investigation into the impact of seismic activities off Vesterålen, a project commissioned by the Norwegian Petroleum Directorate.

The study was one of the largest ever of its kind. It found clear evidence that the fish reacted to the sound of the seismic air guns. The most probable explanation for both the increased and reduced catches for different species and types of fishing gear is that the sound waves produced by the seismic activity stressed the fish, causing them to swim more. This would explain why, for instance, more Greenland halibut were caught in gillnets during the air gun shooting, whereas the longline catches of that species fell. 

NOK 25 million budget

The Norwegian Petroleum Directorate commissioned and financed the project, which had a budget of NOK 25 million.

The seismic survey took place in a limited part (around 15 by 85 kilometres) off Vesterålen known as Nordland VII, where the vessel "Geo Pacific" acquired 3D seismic data 29 June to 6 August 2009. The period was chosen after consultation between the Directorate of Fisheries, The Institute of Marine Research and the fishermen's associations in the counties of Nordland and Troms, during which the seismic activity would cause as little disruption to the fisheries as possible and to avoid spawning periods.

Impact assessment

The task of The Institute of Marine Research was to investigate the impacts of seismic data collection on the prevalence of the species that are fished in the study area.

The findings are presented in the report Effekter av seismiske undersøkelser på fiskefordeling og fangstrater for garn og line i Vesterålen sommeren 2009 ("Impact of seismic surveys on fish distribution and net and longline catch rates in Vesterålen summer 2009").

The Institute of Marine Research's field work started 12 days before the seismic activities began, and continued 25 days after their conclusion. Four hired fishing vessels were used to fish in the area using nets and longlines. The research vessel "Håkon Mosby" used echo sounders and a sonar to map the fish and plankton in the area with a hired fishing vessel. In addition, stomach samples were taken from the fish catches and the sound of the air guns was recorded as well.

Findings

Our investigation into the impact of the seismic activities to the fisheries revealed the following:

- Gillnet catch rates of Greenland halibut and redfish were higher during and after the seismic survey than before it.
- Longline catch rates of Greenland halibut fell during the seismic survey, but rose afterwards.
- Saithe catch rates tended to decrease during and after the seismic survey, but the differences were not statistically significant.
- By-catches of ling in redfish and saithe gillnets tended to increase immediately after the seismic activities commenced, before decreasing after a few days. After the seismic survey was concluded, catch rates returned to roughly the same level as prior to the seismic period.
- Longline catch rates of haddock tended to decrease towards the end of the seismic shooting, when the seismic vessel came closer to the haddock longlines. At its closest, the seismic vessel was within a nautical mile of the haddock longlines.

Confirmation and divergence

The echo sounder data and sonar mapping generally confirmed the catch results. The analyses of the stomach contents of the fish showed no changes that could be attributed to the seismic survey, nor were any changes in plankton distribution discovered during the seismic data collection.

The results of this investigation diverge from the results of previous studies, which one of which found significant reductions in trawl and longline catch rates. However, in the previous study from Nordkapp Bank, seismic activity was concentrated in a smaller area, which meant that the fish were exposed to more intense and continuous sound (number of air gun shots by area and time) than was the case in the area mapped by this study.

 

Contact

Svein Løkkeborg
941 37 809
Ole Arve Misund
79 02 33 05
Kjartan Mæstad
958 08 470