206 THE SCIENTIFIC RESULTS OF V 



fered, although very many less young soles are pro- 

 duced. It is thus quite clear that there is in reality 

 no reserve stock of young to take the place of the 

 adults removed by the special interference of man. 

 The increasing scarcity of the sole is a serious fact, 

 and is thus to be explained. 



From this point of view it is clearly important, if 

 we wish to keep up the number of food-fishes in an 

 area which is fished by man, or to increase that 

 number, that we should (1) either know what are the 

 natural enemies of the food-fish in question at various 

 stages of its growth, and seek to destroy those enemies 

 in proportion as we remove the adult fish ; (2) or, 

 again, that we should isolate and protect the young 

 fish from these natural enemies for a part of their 

 lives ; (3) or, lastly, that we should, in proportion as 

 we remove breeding fish from the area, artificially 

 introduce into that area eggs, or young fish hatched 

 under supervision, so as to supply the deficit created 

 by the fishery of egg-producing adults. 



Any of these operations requires very considerable 

 and most accurate zoological knowledge, and it would 

 be madness to attempt to carry any of them out by 

 proceeding upon hasty guesses or suppositions as to 

 the habits and life-history of the animals concerned. 



There is also no doubt that certain modes of fish- 

 ing and seasons of fishing may be more destructive, 

 more disturbing to the balance of life in a given area, 

 than other modes and other seasons of fishing. The 

 food of the fish which are valued may be destroyed 

 by some of man's operations, their enemies may be 



