- 43 — 



sized plaice is very small, or nil, and the actual trawling catches contain at this time 

 very few such fish, as these are then hibernating, and are not taken by the trawl. In 

 Area C2 the rejection is of very little importance, as the small plaice are very rarely 

 seen here at all; in B2 and Cs it is somewhat more considerable; it occurs also in Ci, 

 but can, for all the other areas, be regarded as nil. • 



At a rough estimate we can reckon, that in the areas A2, As, B4 and B.<î, from twice 

 to three times — at least twice — as many fish are annually rejected from the trawling 

 catches, on account of this market selection, and for the most part uselessly destroyed, 

 as there are landed. This means, for the whole of the North Sea, the useless destruc- 

 tion of about 300 million undersized plaice between 10 and 24 cm. long. The total 

 number of plaice landed from the North Sea by first class vessels has been estimated 

 at roughly 203 million yearly, of which 8i million measure under 25 cm. The total 

 number of North Sea plaice actually caught in the trawl is thus to be reckoned at 

 about 503 million per annum, ranging in length from 10 to 70 cm. Of these 300 + 81 

 or 381 million, amounting to 76 "/o of the total number caught, are undersized plaice 

 under 25 cm. in length, and from i to 3^/2 years old. Of these however, only about 

 16% are landed and turned to use, about 60^ ja being uselessly destroyed. Of these 

 503 million fish, only about 12 million, or a little over 2 "/o, are plaice over 35 cm. 

 long, over 450 grammes in weight, and over 5 years old. 



Composition of the hauls with regard to sex. 



The male plaice are smaller than females of the same age, and are more numerous, 

 in the first four years of life, than the females. In the first year of life the proportion 

 of males to females appears to be abt. 60 : 40, in the following years the relative 

 number of females increases, and from the 5th year of life they are more numerous 

 than the males, and this the more according as the length of body increases. The 

 very largest plaice are invariably female. In all probability, the males do not reach so 

 great an age as the females. From this it is evident that the coefficient of mortality is 

 greater among the males than among the females. 



The males being more frequent in the first years than the females, but more rare 

 later on in life, there must be a certain length at which both sexes are equally numerous. 

 For the southern North Sea, taken as a whole, we can consider 24 cm. as being ap- 

 proximately the length in question, i. e., of all the plaice of 24 cm. in length in the 

 southern North Sea, half are male and half female. In order to arrive at reliable 

 figures, we must of course suppose that males and females were found, in the samples 

 investigated, properly mixed together in the true proportion corresponding to each size. 

 It appears however, that this is not the case, either with regard to time or place. In 

 winter, especially in the spawning months from December to January, and on the spaw- 

 ning grounds for instance of Cs, the males are invariably more numerous in the lan- 

 dings, and still more so in the actual catches: they make up about 80% or more of 

 the total catch. This has doubtless some connection with the fact that females under 

 35 cm. long are, in the southern coastal areas, as a rule not yet mature, while all 

 males under 35 cm. have reached maturity; the greater part of the former hibernate, 



6* 



