68 FISHERIES OF THE NORTH SEA 



seas, especially those of shallow depth, 

 low temperature, and swift currents, con- 

 tain more plankton than other waters ; 

 the submerged North European plateau is 

 especially rich in it, and therefore attract 

 these fish to our coasts in such amazing 

 numbers. 



The herring usually swims in or hear the 

 surface waters, where it finds a greater 

 abundance of these minute organisms on 

 which to feed. Although this food is 

 generally so minute as to be invisible 

 to the naked eye, the fish, by working 

 their gill rakers, which act "as- a sort of 

 filter, sifts the material, and the living 

 substance is retained as food. It will 

 at certain seasons resort to swallowing 

 young pilchard, sprats, its own young, 

 or other small fry. It deposits its eggs 

 on the gravel or stones on the seabed, 

 and the young take two or three seasons 

 to attain maturity. So prolific is this 

 fish that the quantity taken from the 

 North Sea is greater than the total of all 

 other kinds. 



The future problem is how to improve 

 the system of curing, smoking, and pre- 



