u 
Composition in point of age of herring shoals of older age classes. Difficulty 
of investigation. 
It will be sufficiently evident from the foregoing that an elucidation of the important 
question as to the composition in point of age of the herring stock in the North Sea is a task 
which presents grave difficulties. There are in the North Sea several races, the areas 
of developement of which are as yet but little known. We still lack certain information 
as to the rate of growth of the different races, there is for instance some doubt as to whe- 
ther the first winter ring is formed in the first or second winter in the case of the ‘autumn 
spawning fish. There is also the purely practical difficulty that the hauls made by the 
fishermen are carried out with drift nets, which do not furnish samples entirely repre- 
sentative of the actual stock, the younger stages partly escaping. To this must doubt- 
less be added the fact which plays so great a part in the Norwegian waters, viz, that 
the occurrence of the younger year classes exhibits considerable variation, these making 
their appearance sometimes separately, and sometimes mixed, thus causing great fluctu- 
ation in samples from the same locality. 
We are thus still far from being able to finally solve the problem of composition 
with regard to age in the North Sea; further preparatory work is required. It is however 
a question whether it may not already be worth while, for the sake of a preliminary survey, 
to consider some of the many sides of this great question. It would then be natural 
to select for consideration the samples dealt with from the shoals of older spawning or 
mature fish, and endeavour to ascertain how far it may be possible here, as in the case 
of the Norwegian herring, to find some regularity in the composition with regard to 
age of the samples. 
We have seen in the foregoing, that observation of the size of the fish, and the degree 
of development of their genital organs, formed a means by which it was possible, not 
only to distinguish between two samples, one consisting of autumn spawning Shetland 
herring, and the other of spring spawning Norwegian fish, but also to sort out, from 
a mixed sample, the individuals belonging to each of these two races. It is probable, 
that this will be possible to an even greater degree if we take into consideration, not 
only the size and degree of maturity of the fish, but also the age of each individual, and 
the average size of the different year classes in the samples. A knowledge of the general 
results of HEINcKE’S race investigations will also here furnish valuable assistance. 
In the table on page 63 will be found some specimens of the many sample sexamined 
in 1911. The samples have been dealt with from the point of view of composition 
with regard to age, (percentage of year classes) average length for each year class in 
the sample, and maturity. I have here to thank Mr. Pau. BJERKAN for his kind assistance 
in dealing with these samples. 
Different types of composition in point of age. 
Samples 1 and 2 are taken from the north-eastern part of the North Sea (Viking 
Bank). The maturity of the genital organs indicated that most of the fish were spring 
spawning. The May sample (No. 1) revealed genitals recently spent and regenerating, 
the September sample being a mixture, with genitals in varying degrees of development 
towards the large herring stage. These must thus be fish belonging to the Norwegian 
race. The September sample contained, however, some few specimens of spent autumn 
spawning fish. 
