- 44 — 



but the small males which have reached maturity do not hibernate, and are thus caught 

 in the nets. Owing to this superiority in numbers of the males, and the lack of small 

 female plaice, the point of intersection of the male and female curves of frequency is 

 raised considerably, and lies, as a rule, far above 25 cm. In the summer catches on 

 the other hand, the females almost invariably outnumber the males, (by as much as 

 70% or more), and in particular we notice, that many small female plaice make their 

 appearance in the nets, also in the southern areas. Thus the point of intersection of 

 the curves is lowered considerably as against the winter, and lies for the most part be- 

 tween 20 and 24 cm. in the coastal areas; somewhat higher in the deeper waters. 



The true numerical proportion can only be arrived at by comparison of the sexes 

 in all places and at all times. In the southern North Sea we get abt. 50 "/o male and 50 7o 

 female for all the scientific trawl catches together, or, after deducting the small plaice 

 of under 20 cm. in length, abt. 48 7o male and 52^/0 female. In the German plaice 

 landings for 1909, which are subject to the influence of a size-limifof 18 cm., of about 

 260,000 plaice 44 "/o were male and 56 "/o female. The true proportion in the English and 

 German landings probably lies in the middle, and amounts to 46 : 54. If we add to the 

 landings of plaice from the Southern North Sea the large numbers of fish which are 

 rejected from the catches, which measure, for the most part, less than 18 cm., down to 

 10 cm., then the proportion of 46 : 54 of males to females would naturally be so con- 

 siderably altered in favour of the males, that these would certainly become the more 

 numerous. In the northern North Sea, as far as investigations are at hand from these 

 waters, the proportion is in all probability different from that of the southern North Sea, 

 at any rate, in the Scottish fiords, particularly in the Moray Firth. Of about 67,000 

 plaice from scientific catches, ranging in length from 10 to over 80 cm., 53 "/o were 

 male and 4770 female; in the Moray Plrth alone 54 and 46 "/o. Of the Moray Firth 

 plaice from 10 to 17 cm. in length 58 "/o were male, and 42% female, which corresponds 

 approximately to the proportion of the same sizes in the southern North Sea. Of the 

 Moray Firth plaice of 18 cm. and upwards, on the other hand, 54 "/o were male and 

 46 "/o female, or considerably more males than in the southern North Sea. Still greater 

 and more remarkable is the difference in the position of the point of intersection of the 

 sex curves; this lies, for the southern North Sea, approximately between 20 and 28 cm., 

 and for the whole at 24 cm., whereas the length of intersection in the Scottish fiords is 

 about 37 cm. 



These local variations in the numerical proportion of the sexes are in all proba- 

 bility of some importance as regards the question of overfishing. 



3. The composition of the actual stock of plaice in the North Sea, and its 

 probable absolute amount. How great are we to estimate the percentage 

 of the plaice stock, by number and weight, which is taken yearly from 



the North Sea by the fishery? 



It need hardly be said that it is of the utmost importance for a solution of the 

 practical plaice question to have at least an approximate idea of the compositon of the 

 actual stock of plaice in the North Sea and the absolute size of same. 



