A field experiment on the effect of seismic shooting on the lesser sandeel (Ammodytes marinus) was conducted on the fishing grounds in the southeastern part of the North Sea in May 2002. Sandeel buried in the sand at night were trapped in steel frame cages (2.0 × 1.8 × 2.0 m) deployed in positions with high abundance of fish located by a van Veen grab. In an experimental area, three sandeel cages were exposed to full-scale seismic shooting for about 2.5 d. Cameras in the cage and on a remotely operated vehicle (ROV) were used to monitor the activity of the enclosed fish. A control area about 35 km southeast of the seismic shooting area was established with two sandeel cages. The distribution and abundance of the lesser sandeel during daytime in the experimental region were regularly monitored by acoustic surveying, but the present methodology could not demonstrate that seismic shooting caused any change in sandeel abundance. Repeated grab surveys were conducted using a van Veen grab for a predetermined set of localities almost every night during the experimental period, both prior to and after seismic shooting. The results indicate that the seismic shooting had a moderate effect on the behaviour of the lesser sandeel. We did not observe any immediate lethal effect, neither from the cage experiments nor from the grab samples. The total mortality in the cages of about 35% on average, both in the experimental group and the control group, was probably a result of injuries during deployment, due to handling and confinement. Analyses of landing data from the Norwegian sandeel trawlers show a temporary drop in the sandeel landings for a short period after the seismic experiment.

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