Improved mapping of schooling fish near the surface: comparison of abundance estimates obtained by sonar and echo integration

• Published in: Fisheries and Plankton Acoustics. Proceedings of an ICES International Symposium held in Aberdeen, Scotland, 12-16 June 1995 Vol. 53; no. 2; pp. 383 - 388
• Main Authors: Misund, Ole Arve, Aglen, Asgeir, Hamre, Johannes, Ona, Egil, Røttingen, Ingolf, Skagen, Dankert, Valdemarsen, John Willy
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford University Press 01-04-1996
• Subjects: abundance estimation; anchovy; Clupea harengus; echo integration; Engraulis capensis; Etrumeus whiteheadi; herring; Marine; pelagic trawl; pilchard; Sardinops ocellatus; sonar; ANE, Norwegian Sea; PNE, Barents Sea; PSW, Namibia; abundance estimation; anchovy; pelagic trawl; echo integration; herring; pilchard; sonar
• ISSN: 1054-3139; 1095-9289
• DOI: 10.1006/jmsc.1996.0053

A method is described for recording fish schools near the surface by means of a computerized sonar system, a conventional echo integration unit, and sampling by a near-surface trawl. The sonar system consists of a 95 kHz SIMRAD SA950 multi-beam sonar connected to a work station with software for automatic detection and measurement of schools, and logging of the sonar data. The technique for near-surface trawling is based on re-rigging a pelagic trawl by extending the upper bridles, removing the weights, and attaching two large buoys to each wing. Pelagic fish stocks were mapped in the north-eastern Atlantic and off Namibia. The abundance estimates obtained by the near-surface recording method were compared with that obtained by conventional echo integration alone for four different surveys. It is concluded that the near-surface recording method can provide more precise mapping and abundance estimates of pelagic fish stocks in schools near the surface.