Report on herring acoustic surveys in northern and central North Sea during summer 1987

Abstract

Acoustic surveys covering the Northern and Central North Sea were carried out by Scottish and Norwegian vessels during the period 24 June to 11 August. The estimated biomass of mature herring was 817 000 tonnes. For the area north of 57°N the estimate was 553 000 tonnes compared to 534 000 tonnes estimated in July 1986. For this area the estimates by age groups indicate a high mortality on the 1981-1983 year-classes. The estimated number of the 1984 year-class was about twice as large as the estimate for all older age groups together. The 1985 year-class was estimated to be quite strong (13.7 · 10[9]).