In an earlier sketch of the international herring investigations, LEA and the present 
writer*) showed how the figures on which the construction of such average or standard 
scales (Fig. 33) is based, can also be utilised for drawing curves of variation for the growth 
of the herring during different periods, (length of the fish at the age of one year L,, incre- 
ment in second year t,, third t,, etc.). Moreover, it is also possible to ascertain from 
such curves how far a sample consists of fish which are homogeneous in point of growth, 
or contains several different growth-types. 
HEINCKE has previously pointed out that a single feature may in many cases suffice 
to distinguish one race from another; this necessitates, however, examination of a large 
number of individuals. In all probalibity, the study of the growth will be found to furnish 
the most practical means of distinguishing between the various races of herring which 
are found to mix in the North Sea. The greatest efforts are therefore being devoted 
to the treatment of the large number of growth measurements obtained from the North 
Sea samples examined. This important task has been undertaken by LEA, and it is to 
be hoped that the result may form an excellent basis for future closer acquaintance with 
the races and rates of growth of the herring in different parts of the North Sea. By this 
means, valuable light will in course of time be thrown upon the biologically interesting 
question as to the influence of the different natural conditions in this complicated region 
upon the individual growth of the fish and their hereditary characteristics. 
Geographical distribution of the different age groups. 
It is however, also of great importance for the study of the natural history of the 
herring, and thus for the question of race, to investigate the geographical occurrence of 
the different age groups, or the composition with regard to age of the herring in different parts 
of the North Sea. In order to understand the area of distribution of a race it is naturally 
not sufficient to be able to fix the limits of migration for certain stages, as for instance, 
the spawning shoals. Not until we have ascertained where all the different stages are 
to be found is it possible to determine the extent of the area of distribution of the race, 
and define the geographical limits which separate one race from another. If, for instance, 
a certain water is found to contain only older fish, this fact alone is sufficient to indicate 
that the race there represented must have a far more extended area of migration. Thus 
we have in the foregoing seen that in Norwegian waters, the grown herring are found 
principally in the southern part, the immature fish chiefly in the northern regions. No 
investigations on this point have as yet been carried out with regard to the North Sea. 
If we examine the drift net hauls made by the fishermen in the North Sea, it will 
soon be observed that these consist pre-eminently of grown, mature fish. I have alrea- 
dy**) made numerous investigations on this point. It appeared for instance, that five 
steam drifters fishing in the North Sea from the end of May to the beginning of December, 
with a total catch of 14,962 barrels, obtained 
715 barrels or about 4.8°/, fat herring 
14389 — » » 91.4 » fulls, and 
573 —  » » 3.8 » spent fish. 
*) Some results of the International Herring Investigations. 1907—1911, Publ. de Circ. No. 61. 
**) Norsk Havfiske, II. Del, p. 310 ff. 
