732 DEPTHS OF THE OCEAN 



This power of distinguishing the different species in early 

 stages has been of great advantage to oceanography. By 

 securing the eggs and larvae floating in the surface waters, we 

 can decide what species spawn in a definite area. We capture 

 in our silk nets a profusion of different eggs and larvse, and 

 can with certain limitations separate them as belonging to 

 various species, just as we assort the catches of adult fishes 

 Spawning from 3. haul with the trawl. The spawning area of a species 

 can thus be determined by merely taking numerous tow-nettings, 

 and ascertaining the presence or absence of the eggs belonging 

 to the species in question. 



To catch the adult spawners is very often difficult, and takes 

 a long time. The floating eggs can, on the other hand, be 

 taken with the greatest ease, and the simple appliance of the 

 tow-net furnishes an excellent means of ascertaining where the 

 fishes spawn, for most species remain some time underneath 

 the recently spawned eggs. In April 1901- I followed up this 

 reasoning on the coast banks off northern Norway, and 

 succeeded in finding enormous shoals of cod on certain 

 banks, where no fishing was carried on, and where, as a con- 

 sequence of our discovery, millions of cod were afterwards 

 taken. ^ 



Stimulated by this experience I advised the International 

 Council for the Study of the Sea to effect a systematic survey 

 of the spawning areas of the cod family. My proposals were 

 adopted, and an enormous amount of material relating to the 

 natural history of the cod family was accumulated, thanks to 

 the exertions of those on board the Danish, Belgian, English, 

 Scottish, Dutch, Norwegian, Swedish, and German investigation 

 steamers. 



The Danish steamer " Thor," under the leadership of 

 Schmidt, investigated certain parts of the Atlantic and the 

 waters round Iceland. The Norwegian steamer " Michael 

 Sars" examined the Norwegian Sea and the northern portion of 

 the North Sea, while the steamers of the other countries worked 

 mainly in the North Sea. The results obtained through this 

 organisation of the work proved that even closely related 

 species presented certain peculiarities as regards the situation 

 and extent of their spawning places," as shown in the following 

 table : — 



^ Fiskeri og Hvalfangst i det nordUge Norge, Bergen, iqo2. 



^ "Rapport sur les travaux de la commission A dans la periode 1902-1907," Rapports et 

 Proces verba iix dit Conseil iuteniatioiial, vol. x. Copenhague, 1909. 



