MIGRATION OF FISH 95 



north into seas at present uncharted. Who 

 knows but that the North- West Passage 

 may, after all, become an important sea, 

 although perhaps in a way Franklin little 

 imagined ! Cool temperatures and shallow 

 waters are most conducive to the growth 

 of fish, and these Arctic seas perhaps abound 

 in unknown treasures. In springtime 

 thousands of tons of cod-fish are landed in 

 Britain from the shoals which congregate 

 on the Icelandic banks at that season. 

 These enormous shoals arrive with the 

 object of depositing their spawn, and are 

 at the end of a long migration. In future 

 years, as the fishing increases in intensity 

 with the enlargement of the industry, these 

 banks will perhaps sHow signs of depletion. 

 If by that time migration is properly under- 

 stood in its relation to moving masses of 

 plankton and the annual or cyclical change 

 of temperatures and currents, we may be 

 able to trace this migration to its source 

 and find further prolific grounds in the 

 northern seas perhaps far richer than any 

 so far discovered. 



Other kinds of fish have periodic seasons 

 when they "set in " on certain banks. 



