168 FISHERIES OF THE NORTH SEA 



the survivors far away into much deeper water 

 beyond the reach of the apparatus of fishermen. 



There is little doubt but that excessive 

 cold caused the shoals to move away 

 suddenly. Tile-fish prefer warmer currents 

 than the other varieties of cod-fish, and 

 evidently had their habitat in a lower 

 stratum of water which, owing to the ex- 

 cessively cold winter storms of that year, 

 was suddenly invaded by ice. The quick 

 change of temperature, to which tile-fish 

 are very susceptible, would kill off a 

 great quantity, while others, taking fright, 

 would make a wholesale migration, just 

 as certain species of birds would do if our 

 climate were suddenly to change. -Such 

 a catastrophic interference with their 

 normal conditions of life had perhaps 

 caused them to keep away from such an 

 area for many years. 



