336 THE SEAS 



the first year after the war, showing that the fish are being 

 removed at such a rate that they are never allowed to reach 

 a good size. These results may be taken as direct evidence 

 that fishing is being carried on to a dangerously heavy 

 degree. The beneficial effects of fishing up to a certain 

 extent, however, were shown by the fact that after the 

 first year, when large numbers of the old plaice were 

 removed, the growth rate temporarily improved. 



The first care then of fishery research is what is known as 

 a rational exploitation of the sea. That is, that the areas 

 concerned shall be fished right up to their limit, without 

 overstepping it and harming the stock for future years or 

 upsetting too severely the balance of nature. To discover 

 these limits the productivity of the sea must be estimated ; 

 the life -histories of all the fishes, and animals and plants that 

 concern them, must be worked out ; the causes of the 

 various fluctuations that occur from year to year in the 

 supply of different fish must be found and these fluctua- 

 tions must be discriminated from those that may have been 

 brought about by overfishing. 



Although many of the methods employed in fishery 

 research have been mentioned in the above outline of 

 the study of two such fish as the plaice and the herring, 

 there are still others that remain unmentioned. Space 

 will not allow of further expansion on this subject but 

 enough should have been said to impress the reader with 

 the immense amount of labour that is involved in such 

 investigations. We cannot be satisfied with one or two 

 observations only. Day in, day out, information must be 

 gathered from all possible sources ; statistics of fish landings, 

 measurements of fish, samples of the bottom, collections 

 of plankton, observations of currents, temperatures and 

 saltness, all are needed. Furthermore we cannot be content 

 with such information gathered over a period of only one 



