Methods in Oceanography 17 (2016) 206–220 Contents lists available at ScienceDirect Methods in Oceanography journal homepage: www.elsevier.com/locate/mio Full length article Practical calibration of ship-mounted omni-directional fisheries sonars Gavin J. Macaulay a,* , Sindre Vatnehol a , Ole Bernt Gammelsæter b , Héctor Peña a , Egil Ona a a Institute of Marine Research, P.O. Box 1870 Nordnes, N-5817 Bergen, Norway b Kongsberg Maritime AS, Strandpromenaden 50, 3191, Horten, Norway highlights • Calibration is essential for quantitative use of fisheries sonar backscatter. • A method for calibration of ship-mounted fisheries sonars is proposed. • We measured and corrected for the effect of sonar configuration on the calibration. • The accuracy and stability of sonar calibrations are measured. article info Article history: Received 12 July 2016 Received in revised form 27 September 2016 Accepted 11 October 2016 Keywords: Omni-directional fisheries sonar Calibration Echo-integration abstract Conventional ship-mounted vertically-oriented echosounders are poor at detecting organisms that are close to the sea surface. In contrast, omni-directional sonars can ensonify these near-surface waters unavailable to hull-mounted echosounders. If calibrated, sonars can provide quantitative biomass estimates of pelagic ag- gregations. However, for sonars that have not been designed as scientific and research instruments, the quantification and veri- fication of the system performance is of heightened importance, and should include how parameters such as the shape and gain of the beams vary with system and operational configurations. We present a practical methodology for absolute calibration of omni- directional sonars when conventionally mounted on a vessel, il- lustrate the achievable calibration accuracies and precision, and document their variability over time and for a range of operating parameters. This work forms an essential prerequisite to the use of such sonars for quantitative measurement of backscatter, such * Corresponding author. E-mail address: gavin.macaulay@imr.no (G.J. Macaulay). http://dx.doi.org/10.1016/j.mio.2016.10.001 2211-1220/© 2016 Elsevier B.V. All rights reserved.