Aooording to Gilson (1932) 334,000 plaice, 6,963,000 flounder 

 and 264,000 small sole were destroyed in May 1932 alone by 105 

 Belgian motor vessels. Finally Tesoh (1933) estimates that the 

 quantity of non-marketable plaice landed in Hollanpl in 1932 amounted 

 to 345 million fish which were largely older than 2 years o Tesch 

 calculates that by fishing for such small fish, a year class has 

 only 15 percent of its original strength when the fish reach a 

 marketable size. We also have the idea (see po 78 and table 16a) 

 that by using narrow^neshed nets, without avoidance of the grounds 

 where the young plaice are, a year class will have been reduced to 

 about 20 percent of its starting strength when the plaice reach a 

 length of 25 centimeters o 



During the last 10 years before the second World War, it was a 

 frequent occurrence that our fishermen not only did not avoid the 

 grounds where young plaice were found chiefly, but deliberately 

 searched for them. The reasons here werej 1) o the marketable fish 

 had become very scarce, and 2)o all sales of small fish reverted 

 entirely to the crewo Therefore, the crew often received more profit 

 frcsE large catches of small fish than from large ca-fcches of marketable 

 fish. 



The fragmentary observations mentioned will suffice to copvince 

 the reader that the limited fish production of the Worth Sea was 

 handled wastefullyo An enormous wastage took place which we shall 

 have to limit to an unavoidable minimimi if the annual quota of 390 

 million kilograms is to bring in as much money as possible o 



It has been said that if these small fish were not caught, the 

 rate of growth would decline so sharply that the fisher finally 

 would experience more damage than benefit from the protection 

 regulations. Some say that thinning out of the young age groups 

 would be profitable, since more food would be available for every 

 fish and the speed of growth and also the production capacity of 

 the stock would rise. 



It is, therefore, worth while to see what happens when a group of 

 undersized fish is thinned out. Each of these fishes would have 

 needed a certain amount of food to reach a catchable sizej this food 

 would have been used in the first place to keep up the metabolic rat«o 

 With what is left it would have increased the weight. If the stock 

 is thinned out, the rations of the caught fishes will be available for 

 the remaining fish. This increase of rations will be used for weight 

 increase alone. The thinning thus results in the conversion of food 

 which was used for maintenance into fish-weight. The remaining fish 

 will then increase more in weight during the period between thinning 

 and the time of becoming marketable, than they would have done in the 

 past during the same period of time. If the thinning is to be profit- 

 able for the productivity of the fish stock, then the increase in 

 weight must be larger than the loss in fish-weight that came about 

 through the destroying of the undersized fish. The increase in weight 

 corresponds with the ration necessary for maintenance during the period 

 between thinning and becoming marketable. The sipe of the increase will 

 depend on the length of the period. Whether the increase surpasses the 

 loss is, therefore, a question of time. 



36 



