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During the period 12 March to 20 July 1990 the spawning area of the North Sea mackerel was investigated by research vessels from the Netherlands, Denmark and Norway. Based on the plankton samples and temperature observations obtained during this period the egg production and spawning stock size were estimated. The estimated total egg production of mackerel (53 x 10^12 eggs) represents a spawning stock biomass of 78 000 tonnes, which is about twice the estimate in 1988.

Four herring acoustic surveys coordinated by ICES were carried out by Scottish, Norwegian, Swedish and Danish research vessels during the period 28 June to 9 August 1989. The reports on the individual surveys, giving a short description of the survey, and a presentation of the results, are collected in this paper. The combined estimated spawning stock biomasses of herring were 1.6 million tonnes autumn spawners and 255 000 tonnes of spring spawners. The combined results are discussed in the paper.

An acoustic survey in the North Sea, Skagerrak and Kattegat was carried out in July-August 1987 by vessels from Denmark and Norway. This paper gives the distribution and the abundance estimates for mackerel.

Four herring acoustic surveys coordinated by ICES were carried out by Scottish, Norwegian, Swedish and Danish vessels during the period 24 June to 19 August 1988. The reports on the individual surveys, giving a short description of the survey, and a presentation of the results, are collected in this paper.

During the period 22 May to 17 July the spawning area of North Sea mackerel was investigated by research vessels from Scotland, the Netherlands, Denmark and Norway. Based on the 629 plankton samples and temperature observations obtained during this period the egg production and spawning stock size were estimated.