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minaries requisite thereto, as well as the possibilities, difficulties and imperfections 
attaching to such method. 
A characteristic feature of the method is, as we have seen, the comparison of 
results obtained by age analysis of samples with the fishermen’s hauls, as expressed in 
the statements of the fishery statistics, with a view to forming an opinion as to the 
composition of the stock in point of age, the relative numbers of the year classes at 
the moment, and probable consequent size of the stock in the future. It is here pre- 
supposed: 
That it is possible to obtain samples which are truly representative of the stock 
as regards composition in point of age. 
That the longevity of year classes among the different species is generally known. 
That there exists a certain approximate relation, not too closely defined, between 
the size of the stock and the yield of the fishery. 
A final word may here be added as to these three principles. 
Possibility of obtaining samples truly representative of the composition of 
the stock in point of age. 
From Chapters I, II and IV we found that the various shoals of fish exhibited one 
point of difference, i. e. their composition, the mature, spawning fish being remarkably 
constant and homogeneous in this respect, while the young immature fish appear in 
shoals of highly variable composition in regard to age within one and the same year. 
Thus while the samples of large herring, spring herring and skrei were found to correspond 
very closely, the fat herring and Finmark cod were far less constant in this respect. The 
most reliable results should therefore be obtained from the study of the mature fish, 
and it has been found that a comparatively small amount of such material will 
suffice to give a full and reliable survey. As regards the younger fish, greater difficulties 
are here apparent; these need not however, by any means be regarded as insuperable. 
First of all, investigation of a greater number of samples will be necessary, and in addi- 
tion, a closer acquaintance with the laws which govern the migrations of the different 
year classes. Such investigations have therefore already been laid down for 1914. It 
is obvious, that the earlier the period of life at which it is possible to determine the nu- 
merical value of a year class, the greater will be the value of the method as a means by 
which to judge of the future character of the fishery, presenting a longer period of time 
during which the presence of rich year classes is known. 
Possibility of general knowledge as to the longevity of different species. 
The next point of importance is to ascertain for what length of time the occurrence 
of any year class may be reckoned with. It is obviously not sufficient here to take the 
extreme period durmg which some isolated specimens may still be encountered; it is 
necessary to know how long the fish will continue to occur in numbers. In other words, 
it is necessary to know the mortality (or percentage of mortality at different ages). This 
can only be ascertained by experience, based on the observation of many years; it is 
obvious that any accurate scientific determination of the laws which here prevail must 
rest upon continued actual observation of the appearance, presence, and disappearance 
of several rich year classes. It is scarcely to be expected that the mortality will prove 
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