4o After 1 year, the year class is then diminished by 10 percent 

 of IjOOO (natural mortality) and by 7 fish through fishings therefore, 

 at the beginning of the second year 893 fish remaino One=half of 

 this group is caught? that is, of each centimeter group an eighth 

 part of 50 percent of 893 haddock, since the third year is 

 reached at 25 centimeters, etco 



The category of undersized fish taken in both types of nets 

 were below the size thought to be just useful for human consxrnption 

 about 1938« We accepted this limit because we want to Vcnow how 

 much of the fish thrown overboard caught in a mesh-width net of 

 55 millimeters will still be caught by a mesh-width net of 80 

 millimeters.. 



Only a third of the undersized haddock which is destroyed 

 Yfith the narrow net will be caught with' the wider nete Undersized 

 plaice will be caught only 1 l/4 times as much in the 55 milli^ 

 meter cod end as in the 80 millimeter oneo The question remains 

 why the effect of the different cod ends is considerably less 

 for the plaice than for the haddock » 



The explanation of this is as follows s The rate of growth 

 declines because the small fish are sparedo This increases 

 the chance that the undersized fish will be caughto The decline 

 of the rate of gro»/th reduces the effect of the protecxiono The 

 effect of the protection will be even more reduced as the rate 

 of growth of the affected species is smallero The rate of 

 growth of the plaice is appreciably smaller than that of the 

 haddock and this is one of the reasons why, by using an enlarged 

 mesh width, relatively more nonnnarke table haddock will be savedo 

 The second reason is that the 80 millimeter meshes are more suited 

 for the escape of non-marketable haddock than for the escape of 

 undersized plaice o 



While we have concluded that by introduction of minimum sizes 

 alone, the quantity of undersized plaice would be 8 percent of 

 the total plaice catch, we may now conclude that by introduction 

 of a minimum mesh width of 80 millimeters this quantity will decline 

 to 100 I- 125 X 8 = 6o4 percent© The quantity of undersized haddock 

 caught will decrease to one-thirdo We had ass^Mned that by shunning 

 the areas where much young haddock is present, the quantity of 

 undersized haddock would lower to 15 percent© After introduction 

 to the measure, 5 percent would be an acceptable amoxmt of the 

 quantity of undersized haddocko Few undersized fish of cod and 

 other species were caught© We estimate that quantity at 5 percent 

 and expect that this would be halved when the protection regula- 

 tions are introduced© 



According to the estimation on page Z5) the optimum catch 

 in the North Sea would be approximately 390,000,000 kilograms 

 of bottom fish© This includes the non-marketable fish© 



84 



