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dc.contributor.advisorOlsen, Kjell Kristian
dc.contributor.authorJørgensen, Roar
dc.date.accessioned2012-04-19T08:37:59Z
dc.date.available2012-04-19T08:37:59Z
dc.date.issued2004
dc.description.abstractThe general objective of this thesis was to collect improved knowledge about the target strength (TS) of capelin (Mallotus villosus) through experimental studies, as well as to undertake adequate observations of behaviour of capelin during surveying situations, including the effect of different depth distributions and of vessel avoidance. Pre- and post-spawning capelin from the Balsfjord and the Barents Sea stock were observed in a net pen and in a submersible rig with a calibrated 38-kHz scientific splitbeam echo sounder. The net pen experiment showed that the acoustic TS of capelin depended on swimbladder length. In females, TS tended to be negatively influenced by condition. The experiments in the submersible rig demonstrated that the TS of capelin depends on the tilt-angle distribution and ambient pressure. The avoidance reactions of Barents Sea capelin to Norwegian research vessels were studied by means of the Bergen Acoustic Buoy (BAB), which was equipped with a 38 kHz echo sounder. BAB experiments were carried out in the capelin’s feeding area in the Barents Sea in the autumn, and on its spawning grounds in Varangerfjord in North Norway in early spring. There was no significant influence of the avoidance reactions of capelin to survey vessels on the volume scattering coefficient, either in the feeding area or on the spawning grounds. However, there were indications of changes in the centre of depth distribution (diving) before the pass, especially in dense concentrations on the spawning grounds. The findings of this thesis indicate that differences in vertical distribution of capelin in different areas and seasons, or between years with differences in oceanographic conditions or predation, may bias absolute estimates of stock abundance of capelin if the depth distribution of the fish is not taken into consideration. It is therefore recommended that the effects of ambient pressure are included in the TS equation used in surveys in order to make the acoustic stock size estimate of capelin in the Barents Sea a better absolute estimate of the stock abundance.en
dc.descriptionPapers 1-3 of this thesis are not available in Munin: <br/>1. Jørgensen, R., and K.K. Olsen.: 'Acoustic target strength of capelin measured by single-target tracking in a controlled cage experiment', ICES Journal of Marine Science 59: 1081-1085. Available at <a href=http://dx.doi.org/10.1006/jmsc.2002.1239>http://dx.doi.org/10.1006/jmsc.2002.1239</a> <br/>2. Jørgensen, R.: 'The effects of swimbladder size, condition and gonads on the acoustic target strength of mature capelin', ICES Journal of Marine Science (2003), 60:1056-1062. Available at <a href=http://dx.doi.org/10.1016/S1054-3139(03)00115-2>http://dx.doi.org/10.1016/S1054-3139(03)00115-2</a> <br/>3. Jørgensen, R., N.O. Handegard, H. Gjøsæter, and A. Slotte: 'Possible vessel avoidance behaviour of capelin in a feeding area and on a spawning ground', Fisheries Research (2004), 69:252-261. Available at <a href=http://dx.doi.org/10.1016/j.fishres.2004.04.012>http://dx.doi.org/10.1016/j.fishres.2004.04.012</a>en
dc.identifier.urihttps://hdl.handle.net/10037/4115
dc.identifier.urnURN:NBN:no-uit_munin_3835
dc.language.isoengen
dc.publisherUniversitetet i Tromsøen
dc.publisherUniversity of Tromsøen
dc.rights.accessRightsopenAccess
dc.rights.holderCopyright 2004 The Author(s)
dc.rights.urihttps://creativecommons.org/licenses/by-nc-sa/3.0en_US
dc.rightsAttribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)en_US
dc.subjectVDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921en
dc.subjectVDP::Landbruks- og Fiskerifag: 900::Fiskerifag: 920::Ressursbiologi: 921en
dc.subjectVDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fisheries technology: 924en
dc.subjectVDP::Landbruks- og Fiskerifag: 900::Fiskerifag: 920::Fiskeriteknologi: 924en
dc.subjectLoddeen
dc.titleThe effects of behaviour on the acoustic target strength of capelin (Mallotus villosus) and implications for acoustic abundance estimationen
dc.typeDoctoral thesisen
dc.typeDoktorgradsavhandlingen


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Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)
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