— OY 
2) The difference in the composition of the samples with regard to age is due to 
the fact that the numbers of the year classes varied, and especially to the circumstance 
that one year class, that dating from 1904, was far more numerously represented than 
the others. 
The very important question now arises, whether these results should be considered 
as due to fortuitous conditions in the three samples, or to natural variation in the stock 
of the fat herring as a whole. Can we, from these observations, deduce a general law? 
It is evident, that only experience, obtamed by the examination of many samples and 
covering several years, can enable us to answer this question, and, since the point is 
of fundamental importance for comprehension of the composition with regard to age 
and size, and of the fluctuations in the herring fishery, I will endeavour to show what 
conclusions may be drawn from the material at present available. 
The samples of fat herring examined in the years 1907—1909 were as follows*): 
No. of No. of specimens 
samples therein contained 
107. 5 c+ 12 2383 
1908 8 2398 
1909 3 1958 
Total 23 6739 
In 16 of these 23 samples, the year class 1904 was found to be represented by a 
percentage of over 40. In spite of this, however, the average percentage for the year 
class in all the samples is only as follows: 
in 1907, 51.3%, in 1908, 37.8, in 1909, 16.9. 
A comparison of all the different samples clearly shows to what this is due. Several 
samples are found to contain a large admixture of small herring, the 1?/, and 2?/, year 
fish, which are entirely lacking in other samples. Of the 1?/, year fish, a single sample 
contained 91.9%. In 1908 there were in one sample 93.9, in another only 3.6 %, 
of the 2?/; year fish. Far more certain results could have been obtained by taking out 
all the younger fish, but as the question of the movement of the younger year classes 
in shoals is as yet only imperfectly investigated and understood, I prefer not to make 
any attempt in this direction. We will mstead proceed to consider the composition 
in point of age and size of the older classes of fish, the large herring and the spring 
herring. 
Year class 1904 among large herring and spring herring. 
As regards the large herring, figures are available for the years 1909—1913; in the 
case of the spring herring, from 1907—1913. The average percentages of the 1904 class 
for all samples from these years are given in the table below, in which, for the sake of 
convenience, I have also included the mean figures for fat herring in the years 1907— 
1910. 
*). The results of the age determinations in each individual sample will be found in the tables 
on pp. 31-34 in Publ. de Circ. No. 61, Copenhagen 1911. 
