SCHOOLING BEHAVIOUR OF SARDINE SARDINOPS SAGAX IN FALSE BAY, SOUTH AFRICA

The schooling behaviour of sardine Sardinops sagax in False Bay on the south coast of South Africa was studied in October 1995 using high-resolution sonar and a hull-mounted, echo-integration unit. School formation and disintegration were studied, and school shape, packing density, swimming behaviour and inter- and intra-school event rates were quantified. Mean fish density was 29.5 fish m-3 (SD 46 fish m-3), but it varied between schools by a factor of about 100 (from 2 to 233 fish m-3). Tracked schools moved at average speeds of 0.67–1.59 m s-3. Schools changed shape on average every 2.08 minutes, and underwent either splits or merges with other schools on average every 5 minutes. Relationships between the geometric dimensions and biomass of the schools were established.Afr. J. mar. Sci. 25: 185–19

Protocols for calibrating multibeam sonar

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 2013-2027, doi:10.1121/1.1869073.Development of protocols for calibrating multibeam sonar by means of the standard-target method is documented. Particular systems used in the development work included three that provide the water-column signals, namely the SIMRAD SM2000/90- and 200-kHz sonars and RESON SeaBat 8101 sonar, with operating frequency of 240 kHz. Two facilities were instrumented specifically for the work: a sea well at the Woods Hole Oceanographic Institution and a large, indoor freshwater tank at the University of New Hampshire. Methods for measuring the transfer characteristics of each sonar, with transducers attached, are described and illustrated with measurement results. The principal results, however, are the protocols themselves. These are elaborated for positioning the target, choosing the receiver gain function, quantifying the system stability, mapping the directionality in the plane of the receiving array and in the plane normal to the central axis, measuring the directionality of individual beams, and measuring the nearfield response. General preparations for calibrating multibeam sonars and a method for measuring the receiver response electronically are outlined. Advantages of multibeam sonar calibration and outstanding problems, such as that of validation of the performance of multibeam sonars as configured for use, are mentioned.Support by the National Science Foundation through Award No. OCE-0002664, NOAA through Grant No. NA97OG0241, and the Cooperative Institute for Climate and Ocean Research (CICOR) through NOAA Contract No. NA17RJ1223 is acknowledged

Observations on the near-surface behaviour of sardinella schools in Angolan waters

The schooling dynamics and swimming behaviour of sardinella Sardinella maderensis and S. aurita schooling near the surface in Angolan waters were recorded visually, using a calibrated echo integration system and a 95kHz high resolution sonar on board RV Dr Fridtjof Nansen during three cruises; July 1996, May 1997 and May 1998. The mean packing density of the sardinella schools was about 3 fish m–3, but this figure varied by two orders of magnitude among the schools. There was a linear relationship between the area and the biomass of the schools, which can be used in future surveys to convert recordings of school area by camera, lidar or sonar to school biomass. The sardinella schools swam at an average horizontal speed of 1.24m s–1, mostly towards or away from the coast. The schools seemed to be feeding near the surface and behaved rather dynamically. Intra-school events such as change of shape, reorganisation, splitting and leaving occurred every 2.4 minutes on average. Inter-school events such as approach and join was every 14.2 minutes on average. The schools were visible on the surface in the morning and in the afternoon, but seemed remarkably undisturbed by predating birds, fish and seals during the day. It is suggested that the low predation activity near the surface enables the sardinella to exploit plankton prey that is concentrated at surface fronts of internal waves and along the convergence lines of coastal and oceanic currents. African Journal of Marine Science 2005, 27(1): 169–17