190 BRITISH FISHERIES 



which shows how much fishing operations tax 

 the population of the sea. 



In the sea and on the land one form of animal 

 life depends for its sustenance on the capture and 

 utilisation as food of some other form of life. It 

 is easy to trace this in the case of any particular 

 animal, such as man. A large portion of our own 

 food consists of the flesh of other animals, and the 

 remainder is some form of vegetable tissue. We 

 know from constant observation the animals on 

 which the fishes used as food by man feed. In 

 the case of cod, we find that an almost constant and 

 favourite form of food consists of crabs of various 

 kinds. The cod (which is one of the foods of 

 man) therefore feeds on the crab, and it now 

 becomes our object to determine the food of this 

 crustacean. The crab is catholic in its tastes, but 

 we shall, in many cases, find it feeding on various 

 worms inhabiting the bottom deposits of the sea, 

 and these worms again we shall often find feeding 

 upon the smaller Crustacea (among other things). 

 Pushing our inquiry still further, we may find 

 these smaller Crustacea feeding upon the copepods 

 which live in the mud, and with these micro- 

 crustacea our chain of animal forms which are 

 linked together as the food and sub-foods of the 

 cod (and man) comes to an end. Or if we take 

 the plaice, again, as another food of man, we can 

 establish another, though shorter, series. This 

 fish usually feeds on small bivalve shell-fish living 



