— 209 — 
have been observed throughout a whole series of years having been found to maintain 
their original relation to other year classes in this respect. Only the further experience 
obtained by many years of future observation can, however, determine how far this 
can be regarded as constantly or generally the case. 
Importance of future investigations as to the causes of numerical variation. 
It will be evident from the foregoing, that a study of the conditions which determine 
the numerical value of the year classes can only attain its object when based upon a 
very extensive plan. As a matter of fact, the object can never be fully attained; new 
questions will constantly arise, as the knowledge obtained creates the demand for new, and 
it will always be possible to increase and intensify our comprehension of the vital con- 
ditions affecting the organisms in question. A study of the fluctuations in the popu- 
lation of the sea, both fish and smaller organisms, and thus of the whole organic life 
existent in the ocean, is therefore the soundest possible basis for marine research, whether 
with theoretical or practical ends in view. There is moreover, scarcely any other que- 
stion which is so well calculated to focus the attention of men engaged upon different 
branches of science, as this must necessarily be the case where several investigators 
are at work on board the same vessel. 
The constantly increasing knowledge of the hydrographical and biological condi- 
tions upon which the numbers of the organisms, and especially of the fish, so greatly depend, 
will naturally be of the greatest importance. Perusal of the mass of fantastic guesses, 
assertions and suggestions which have been published in various works or in the press, 
with the object of combating these fluctuations, will suffice to show that only to have 
led the general trend of ideas into a right or reasonable direction would in itself be 
an achievement worth all the amount of work involved. 
In the interest of biological research, also, it must be of the greatest importance 
to ascertain the nature of the laws which govern the renewal of the animal population, 
especially when taking into consideration all that has been written from time to time 
about overpopulation and the struggle for existence in the animal world, all from the 
point of view of human conditions. 
It is, however, by no means impossible that practical results also may be attained 
by this means. In particular much might be learned which would serve to elucidate 
the old questions of pisciculture or incubation, in regard to which the lack of progress 
and insufficient comprehension of results have long been felt. Once it is possible to 
indicate with certainty the conditions which determine whether great mortality is to 
take place among the young stages or not, the whole position as regards these questions 
may be altered. No definite opinion can of course be expressed as to this until the pro- 
blems have been solved. It is gratifying to observe, however, that the International 
Council has now decided to work towards this end. 
The knowledge obtained will also be of great practical value in considering the que- 
stion of possible decrease in the stock due to overfishing, and will at least serve to show 
that the statement of the fishery statistics can only be safely employed for the 
elucidation of these problems, when the fluctuations due to natural causes. are 
known. 
to 
= 
