types 
1911 (No. 9). These three samples, (3, 4 and 9) thus support HEINcKE’s theory, viz, 
that the Bohus herring (spents) consist in winter of fish which have spawned in the autumn 
in the North Sea, especially on the Jutland Bank. The samples from Bohuslan, Fe- 
bruary 1911 (10 and 11), on the other hand, reveal so strong an admixture of fat herring 
that the composition in point of age is thereby altered. 
Autumn spawning fish are also found in the Kattegat in the autumn, samples 5, 6, 
7 from 1910 and 12, 13, 14 from 1911. These fish doubtless differ considerably from 
the autumn herring of the North Sea, and should probably be regarded as a local race 
belonging chiefly to the Kattegat. x 
Fat herring oceur, as will be seen, in considerable quantities everywhere throughout 
the Skagerak and Kattegat; at Risor and Langesund on the Norwegian side of the Skage- 
rak (samples 1 and 8) on the Jutland Bank (2 and 9) and in most of the samples from 
Bohuslän and the Kattegat. 
The samples thus confirm the idea that the Skagerak and Kattegat have a mixed 
stock of herring, consisting of immigrant ocean herring, both spring spawning Nor- 
wegian fish and especially autumn spawning North Sea fish; autumn spawning Kattegat 
herring; probably spring spawning coast herring; and, in addition, a large number of 
young fat herring. 
The Skagerak and Kattegat form nurseries for great numbers of herring; the great 
fisheries, however, are based upon the large shoals of ocean fish which spawn in the aut- 
umn out in the North Sea, moving in during the winter towards the coast of Bohuslan. 
Similar large immigrations — of spring spawning Norwegian ocean herring — most 
probably take place in certain years, along the Norwegian coast of the Skagerak towards 
the mouth of the Christiania Bion and the northern part of the Bohuslän coast. 
Variations in age composition from year to year. 
We have hitherto only considered the age composition of the North Sea herring 
for a single year. It is evident, however, that a comparison of several years in this re- 
spect, as in the case of the Norwegian herring, is necessary in order to discover the charac- 
teristic regularity in the average composition of the stock, and in the variations of this 
composition. The international herring investigations in the North Sea are af com- 
paratively recent date; for the years 1910—1912 however, I am in a position to state 
the results of the investigation of samples from the Shetland and Lowestoft districts. 
Fig. 42 shows the composition in point of age of five samples from Shetland 
waters, viz. 
Ey: 
2) Winter 1910—1911. 
3) May 1911. 
4) June 1911. 
5) July 1911. 
The two uppermost figures for July 1910 and the following winter show a fairly 
equable representation of the year classes 1903, 1904 and 1905. From May 1911 to 
