Abundance estimation of Norwegian spring spawning herring wintering in the Vestfjord system, December 1996
Original version
This report is not to be cited without prior reference to the authorsAbstract
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.