REPORT OF THE STUDY GROUP ON RECRUITMENT VARIABILITY IN NORTH SEA PLANKTIVOROUS FISH (SGRECVAP)

The ICES Study Group on Recruitment Variability in North Sea planktivorous fish (SGRECVAP) met in early May 2007 to further consider the population dynamics (especially recruitment) of herring, sandeel and Norway pout in the North Sea. SGRECVAP first met in 2006, when worries were expressed about the apparent synchronous serial poor recruitment in those species since 2001. The second meeting of SGRECVAP in 2007 found that the residuals from the stock to recruit curves for Norway pout and herring still expressed similar trends despite the recent better recruitment in Norway pout, whilst there was no trend in the residuals of sandeel. A detectable change in the recruitment of herring and Norway pout in the North Sea was either caused by a reduction in productivity in the early 2000s or by a longer cycle of decline since the 1980s. There was only a biomass signal on the recruitment of sandeel. The productivity of all three stocks is low at present.The lack of any properly funded research project on the recruitment of planktivorous fish in the North Sea meant that the activities of SGRECVAP were limited to list potential hypotheses, stimulate further investigations and carry out preliminary analysis. Data sets of environmental data were compiled to explore the hypotheses listed by SGRECVAP 2006. Specifically wind, temperature, water density, water colour, flow, copepods, chaetognaths, total zooplankton, nauplii, the ratio of Calanus finmarchicus and Calanus helgolandicus and the abundance of predatory fish were investigated.