Acoustic mapping of pelagic fish distribution and abundance in relation to a seismic shooting area off the Norwegian west coast

TitleAcoustic mapping of pelagic fish distribution and abundance in relation to a seismic shooting area off the Norwegian west coast
Publication TypeJournal Article
Year of Publication2004
AuthorsSlotte, Aril, Hansen Kaare, Dalen John, and Ona Egil
JournalFisheries Research
Volume67
Pagination143-150
ISBN Number0165-7836
EndNote Rec Number8595
Keywordsabundance, Blue whiting, distribution, herring, Mesopelagic fish, Seismic shooting
Abstract

In April 1999 seismic investigations started in an area off western Norway as part of an ordinary three-dimensional survey, using a vessel with two seismic sources, each of 20 air guns and 10 hydrophone streamers. The seismic sources, towed at a depth of 8m, were alternatively fired every 25m along 51 transects, each 51525m long, separated from adjacent transects by 500m. The possible influence of this seismic activity on pelagic fish (herring, blue whiting and mesopelagic species) was investigated in two ways. First, the distribution and abundance within the seismic area and the surrounding waters up to 30–50km away were mapped acoustically three times. In all three surveys the acoustic abundance of pelagic fish was higher outside than inside the seismic shooting area, indicating a long-term effect of the seismic activity. Secondly, the acoustic abundance was recorded directly prior to and after shooting along some of the seismic transects. In these comparisons no differences were found, indicating that the shooting had insignificant short-term scaring effects. However, both blue whiting and mesopelagic species were found in deeper waters in periods with shooting compared to periods without shooting, indicating that vertical movement rather than horizontal movement could be a short-term reaction to this noise.