— 20 — 



investigations with regard to the cod have been brought to a conclusion, 

 though only a temporary one; the herring investigations are still in progress. 



We have here to deal with a theoretical question of great practical impor- 

 tance. Certain fish — here chiefly fish of economical importance — are found 

 throughout the whole year in nets which work a certain sea district, while 

 others appear in one or another sea area, or on one or another coast, only at 

 certain seasons of the year. And with regard to these fish, especially cod, 

 herring, mackerel, sardine etc., it has for many years been observed that the 

 proceeds of the catches is subjected to great fluctuations from year to year, 

 the fish appearing one year in great shoals, and the next being far less 

 numerous or even scarce. Cases are even cited in literature of coasts which 

 had long been regularly visited by one or other of these fish, being suddenly, 

 and often for several years at a time, deserted by them. The question 

 naturally arises, whether the fish in question had simply sought other grounds, 

 or whether they were non-existent, or greatly reduced in numbers, during 

 those years. The non-appearance of such fish, and the consequent failure of 

 a certain branch of the fishery, must naturally mean a very serious loss to 

 the fishermen. An attempt must therefore be made to discover the cause of 

 these apparently great irregularities in the appearance of the fish concerned. 

 As already mentioned these investigations, as far as regards the cod and allied 

 species, have been brought to a temporary conclusion. And although the 

 problem cannot yet be regarded as solved, the earlier vague conjectures as to 

 the occurrence and migrations of this fish have taken far clearer and more 

 certain form. The migrations of each species, as well as of the individual 

 stages of each species have their peculiarities, which it has been especially 

 necessary to learn to know. As regards the relation between the migrations 

 or occurrence of fish and the physical conditions of the sea, it has appeared 

 that since the necessities of life are not the same at all stages of growth, and 

 do not lie within the same boundaries, it is necessary to closely study the 

 areas of distribution of the different stages and their natural conditions, in 

 order to know the influence of these physical conditions. 



The question of the possibility of determining the relation between 

 the stock of older fish and the increase in eggs, larvœ, or young fish, 

 has been in many respects elucidated by the investigations. First of all, 

 however, it was necessary to learn to know and sharply distinguish the 



