340 THE SEAS 



generation at any rate will be thankful that research was 

 started so many years ago, for oceanographical research 

 is but in its infancy. At this day it is little more than 

 fifty years of age, and in fact it is only in the twentieth 

 century that sufficient observations of a routine nature 

 have been collected for comparison with future years. 



It seems doubtful whether man will ever succeed in 

 actually increasing the productivity of the sea, although 

 even that may not be outside the bounds of possibility. 

 At any rate it is improbable that fish-rearing carried out 

 on its present scale will produce any appreciable effect 

 on the fish population ; for what are the few million young 

 liberated to the many million already present in the sea ? 

 It is certainly desirable that they should be reared to more 

 advanced stages than is at present done. Whether 

 eventually fish hatching and rearing could be carried out on 

 sufficiently large a scale to produce any economic results 

 the future must decide ; at least at the present day the 

 capital expense of such an undertaking precludes its 

 possibility. 



It has been shown that the main cause of the productivity 

 of a given area lies in the quantity of dissolved nutrient 

 salts present in the upper water layers (page 219), and an 

 increase in these salts would probably give rise to a greater 

 abundance of fish life. It may be that in years to come a 

 means for so doing will be found : there is a vast reservoir 

 of nutrient material in the deep waters of the oceans to be 

 drawn upon. Already the manuring of estuarine waters has 

 been suggested as a practical means of improving shellfish 

 cultivation. 



But the aims at the present day must lie rather in 

 estimating the limits to which the fisheries will bear 

 depletion, and in collecting information that will enable 

 a forecast of the state of any fishery to be made some time 

 in T advance. Beyond that it is premature to express opinion . 



