Sammendrag
Low frequency (26 - 30 kHz) omnidirectional fisheries sonars (Simrad SX90 and SU90) were
used to measure the acoustic backscatter and dimensions of herring (Clupea harengus) and
mackerel (Scomber scombrus) schools from fishing vessels between 2012 and 2014. Detailed
sonar sampling of each school included operations at slow vessel speeds and fixed distances to
the school, similar to pre-catch school inspection procedures during commercial fishing.
Calibrated digital sonar data were processed using new school segmentation procedures,
including school area correction procedures. Data on segmented schools from horizontal and
vertical sonar beams were used to compute school volume and mean acoustic backscattering
strength (Sv). Using mean lateral target strength estimates and fish length and weight, individual
school biomass estimates were derived. Biomass estimates were compared with purse seine
catches of the same schools, and the accuracy of the estimates assessed in relation to the significant
parameters used.
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