Feeding herring schools do not react to seismic air gun surveys

Abstract

Abstract Peña, H., Handegard, N. O. and Ona, E. 2013. Feeding herring schools do not react to seismic air gun surveys. – ICES Journal of Marine Science, 70: 1174–1180. The real-time behaviour of herring schools exposed to a full-scale 3D seismic survey off Vesterålen, northern Norway, was observed using an omnidirectional fisheries sonar. Throughout the study period, the herring swam slowly against the predominant northeast current, with a net displacement along with the current. The mean swimming speed after subtracting the drift velocities was 0.35 m s−1, and the mean response speed in the direction away from the air gun array was 0.22 m s−1. No changes were observed in swimming speed, swimming direction, or school size that could be attributed to the transmitting seismic vessel as it approached from a distance of 27 to 2 km, over a 6 h period. The unexpected lack of a response to the seismic survey was interpreted as a combination of a strong motivation for feeding, a lack of suddenness of the air gun stimulus, and an increased level of tolerance to the seismic shooting.