As with th© haddock it is olear that the biological lower limit 

 of the minimvon size increases when the fishing intensity increases o 



If, in the future, we maintain the density of the stock at a 

 value corresponding with the optimum catch, then the total mortality 

 will be 50 percent. The biological lower limit of the minimim size 

 is then at most 15 centimeters. Now, we have to see if it is desirable 

 to increase the size for other reasons. 



The prices of the various market divisions of plaice ares 



1946 



Average 1933-38 



Undoubtedly one recieves considerably higher prices for plaice 

 i^ the smaller ones are left in the sea longer, but in general they 

 have to be caught before they reach a length of 40 centimeters and 

 lower in price again. 



We have seen on page 61 that it is difficult to set a minimum 

 mesh width larger than 8 centimeters when c onside ring the losses of 

 roundfish and sole. Figure 5a shows that with a cod end of 8 

 centimeter mesh width, no plaice more than 16 centimeters in length 

 escape. About half of the plaice of 15 centimeters escape. The 

 width of the plaice makes it necessary that a net, from which most 

 of the non-marketable plaice can escape, has to have meshes of at 

 least 12 centimeters. Although fishing is usually done for one 

 particular species, considerable quantities of other fish usually 

 are taken incidentally. A mesh width of 12 centimeters would be 

 suitable for the plaice fishery but would lose most of the marketable 

 roundfish and sole (the sola can roll itself up, so that it can 

 escape through much narrower meshes than the other flatfish). 

 Therefore, we have to find another method to protect the non-*iarke table 

 plaice. It is, therefore, necessary to observe the life history 

 of the plaice. 



The plaice spawns from January to March in the whole southern 

 part of the North Sea, The eggs are most numerous in the Flemish 

 Bight, particularly where there is wann water with high salinity 

 content (Redeke, 1909), The developing eggs are transported by the 

 Rest stream to the North Sea, along the continental coast. First, 



68 



