As shown by several authors, Hjort, Delsman, Bjerkan 1 ) a. o. 
the drift-nets used by the herring fishers in the North Sea are adapted 
to the capture of grown herring of the size frequenting the different 
fishing-grounds. Special implements must thus be used to obtain in¬ 
formation as to the distribution of the younger, immature age-groups 
of the herring. 
Investigations on the younger age-groups have previously been 
made at many places on the coasts bordering the North Sea; as, for 
instance Scotland (Firth of Forth, Murray Firth), England (Plymouth), 
Holland, Germany and Denmark. No closer investigation has, however, 
been made about their distribution in the open waters of the North 
Sea and of their subsequent growth and habitat. It is also of great 
difficulty to study these conditions on the open coasts of the North 
Sea, the service of a steamer and implements of many kinds being 
required. 
In 1912 Dr. Johan Hjort therefore made several cruises in the 
North Sea with the Norwegian research steamer „Michael Sars“ espe¬ 
cially for the purpose of studying the distribution of the younger stages 
of the herring, accompanied by his assistants, E. Koefoed and E. Lea. 
The cruises were carried out in June—July, and October—November 
in order to compare the conditions prevailing in the summer with those 
of the autumn. 
9 Johan Hjort: Fluctuations in the great Fisheries of Northern Europe, Rap. 
& Proces-Verbaux, Vol. XX Cons. perm, intern, p. expl. de la mer. Copen¬ 
hagen, 1914. 
H. C. Delsman: Uber das Wachstum von Nordseehering und Zuiderseehering nach 
Untersuchungcn an den Schuppen, Rapportcn en Verhand. Rijksinstituut 
voor Visscherijonderzoek. Deel I. Afl. 2. S. Gravenhage, 1914. 
Paul Bjerkan: Age, Maturity and Quality of North Sea Herrings, Rep. on Norw. 
Fishery and Marine Investigation. Vol. Ill, No. 1. Bergen, 1917. 
9 
