Abundance estimation of Norwegian spring spawning herring wintering in the Vestfjord system, December 1996

The spawning stock of Norwegian spawning herring has been surveyed when wintering in the Vestfjord, Tysfjord, and Ofotfjord, in northem Norway in December 1996. The basic method is that of echo integration, with compensation for acoustic extinction. Physical capture has been effected by means of the Multisampler pelagic trawl, which allows remote opening and closing of each of three codends at arbitrary depths. This has shown essentially thorough mixing of the dominant year classes except in the two fjord arms, where the samples contained a larger proportion of older fish (1983 year class). Geostatistics has been employed to describe the spatial structure and to provide an estimate of variance. Data quality control procedures have been performed and are described