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dc.contributor.authorHjellvik, Vidar
dc.contributor.authorGodø, Olav Rune
dc.contributor.authorTjøstheim, Dag
dc.date.accessioned2007-06-06T07:25:19Z
dc.date.issued2005
dc.identifier.issn0706-652X
dc.identifier.urihttp://hdl.handle.net/11250/108193
dc.description.abstractDiurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%–50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be reanalysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring.en
dc.format.extent1252337 bytes
dc.format.mimetypeapplication/pdf
dc.language.isoengen
dc.subjectcoden
dc.subjecttorsken
dc.subjectherringen
dc.subjectsilden
dc.titleDiurnal variation in acoustic densities: why do we see less in the dark?en
dc.typeJournal articleen
dc.typePeer reviewed
dc.source.pagenumber2237-2254en
dc.source.volume61en
dc.source.journalCanadian Journal of Fisheries and Aquatic Sciencesen
dc.source.issue11
dc.identifier.doihttp://dx.doi.org/10.1139/F04-161


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