— 42 — 



"young fish grounds", and there again greatest at such times as the densest shoals of 

 these young plaice occur. 



In order to obtain a more or less correct idea as to the actual quantity of young 

 undersized plaice which are annually destroyed in the North Sea, it is necessary to 

 compare the analyses of the scientific hauls with those of the market samples from the 

 same water, and the same period of the year. These investigations have now been 

 carried out to a certain, though not yet sufficient, extent. 



It appears, that when a catch sample, by means of rejection of the small plaice of 

 less value, becomes a market sample, the individual numbers of both will be inversely 

 proportional to those percentages of same which were not affected by the selection. The 

 portion not afiected b)' the selection will consist of those parts of the measurement 

 series which lie at or above the value of greatest density or dividing value, it being taken 

 for granted, that the fishermen accept all plaice of this size and upwards, rejecting only 

 those of smaller size. 



By means of such a calculation we obtain the following figures, which show how 

 many times greater was the rejected, unused portion of the actual catch than the por- 

 tion landed and consumed (the latter being taken as lOo). The value of greatest den- 

 sity or dividing value of the market samples in the areas with which we are here 

 concerned, lies a rule between 24 and 25 cm. often still lower. It is obvious, that the 

 number of rejected plaice will, cœteris paribus, be higher, the higher the dividing value 

 lies. The height of this is again naturally to a great extent determined by the height 

 of the legal or practically accepted size-limit. The figures here given are calculated 

 from German and English investigations, and are thus subject to the influence of a 

 size-limit of 18 to 20 cm. 



Proportional relation of the number of rejected plaice to that of the fish landed, 



in a trawler catch. 



We see, that in the southern coastal areas A3 (and in any case also A3) B4 and Bs, 

 in the summer months from June to September, the number of plaice rejected and thrown 

 away (most of them being from 10 to 20 cm. long) is generally from twice to five 

 times as great as that of the plaice actually landed: it can, in exceptional cases, be 

 twenty times as great, or more. In the winter months the number of rejected under- 



