Hydrographic investigations in the North Sea during the international conjoint herring survey, 1960/61

From tbe beginning of' l":be investigations of the International Council for the Exploration of the Sea (ICES) the fluctuations in the environmental life-history of fish, conditions, having a profound influence on the particularly on migration and occurrence, have been constantly borne in mind. Because of the special nature of the sea and fishery research, our knowledge of the dynamical processes, which have such a decisive influence on the size, the changing composition, and thP- expansion and migration of fish, can only be completed by a close international co-operation.This was the reason why the Herring Committee of ICES when considering the pattern of recruitment in the various stocks of herring in the North Sea called for joint surveys by various countries and for a close collaboration of fishery biologists and hydrographers. Research cruises were carried out by Danish, British, Dutch and German research vessels in spring and autumn l96o and l961 to make a large survey of juvenile herring in the North Sea. The present contribution deals with the meteorologicaJ and hydrographic results of the four research cruises of the International Conjoint Herring Survey 1960/ 6l. Their publicat ion will, above all, give fishery biologists a survey of these environmental influences and thus enable them to evaluate their own material, of them in the light The preparation and evaluation of the environmental data proceeded under a coordinating group consisting of K.P.Andersen (Danish Institute for Fisheries and Marine Research, Charlottenlunct), R.E.Craig (Marine Laboratory, Aberdeen), L.Hannerz (Fishery Board of Sweden, Goteborg), A .. J.Lee (Fisheries Laboratory, Lowestoft), J.A.van Duijnen Montijn (Royal Netherl. Meteorol,Institute, De Bilt), G.Wurlitzer (seewetteramt, Hamburg) and J.J.Zijlstra (Fisheries Research Institute, IJmuiden) with myself as Rapporteur. I am much obliged to tbe group for their co-operation which was so useful in the realization

of this work.