CHANGES IN THE SPATIAL-DISTRIBUTION OF AUTUMN SPAWNING HERRING (CLUPEA-HARENGUS L.) DERIVED FROM ANNUAL ACOUSTIC SURVEYS DURING THE PERIOD 1984-1996

A time series of abundance data for North Sea autumn spawning herring during the period 1984-1996 was reconstructed from the ICES coordinate d acoustic survey reports. The long-term trends in spatial distributio n of three age categories (2, 3, and 4+ group) were visually interpret ed from contour maps and analysed using Generalized Additive Models. I n general the two analyses revealed the same trends and showed a disti nct northward shift of distribution with increasing age. The most nort herly extent of distribution occurred during the late 1980s and in 199 0. This coincided with a period of low recruitment of 0 group fish and relatively high spawning stock biomass. In contrast there was a disti nct southerly shift in distribution from 1991 to 1993 when recruitment was seen to rise and biomass started to fall. This paper hypothesizes that marked year to year shifts in the distribution of the herring st ock may contribute to the processes governing recruitment. (C) 1998 In ternational Council for the Exploration of the Sea.