— so - 



third year upwards, would thus amount to from 1257 to 2515 millions; probably, (with 

 a fishing coefficient of 0.33) 1509 million fish. If we calculate the plaice-fishing area of 

 the North Sea at roughly 300,000 sq. km. (a somewhat uncertain estimate) we get an 

 average of S,000 plaice for each sq. km. area in the North Sea. If we estimate the 

 average area fished by a trawler in an hour at roughly 100,000 sq, m., we get ten 

 trawling hours per sq. km., which gives 500 plaice per trawling hour area, or 5 per 

 1000 sq. m. or one plaice per 200 sq. m. Supposing the fishing coefficient to be 0.40, we 

 should then get 420 plaice to the trawling hour area, or 4.2 per lOOO sq. m. or one 

 plaice per 240 sq. m. As the research steamers have, in the shore areas during sum- 

 mer, taken up to 2,500 plaice from about 10 cm. long and upwards per trawling hour, 

 then these extreme cases would, if we accept the catch coefficient based on the experi- 

 ments mentioned on p. 47 viz., 0.25, give an occasional actual density of the true stock 

 of 10.000 plaice per trawling hour area, which would thus be about twenty times as 

 great as the average. Against this greatest possible density we have, in certain parts 

 of the Northern North Sea, a minimal of O plaice for a whole series of trawling 

 hours. 



All these estimates and calculations as to the actual size of the stock of plaice in 

 the North Sea are evidently very uncertain, since most of the factors in the calculation 

 are not yet fixed, and of only very varying approximate value. I am, however, of 

 opinion, that the figures here given are at present the only ones which can make any 

 claim to a certain scientific value. 



III. 



Are any signs apparent of an actual overfishing or essentially increased 

 tax on the plaice stock of the North Sea through the increased fishing? 



/. The decrease in the number of large and increase of small plaice in the catches qs a 

 probable sign of permanent alteration effected in the composition of the stock of fish. 



The results of the international investigations on this point are as follows: 

 It is impossible to know the real alterations which have taken place in the stock 

 of plaice in the North Sea since the introduction of more intensive fishing by means of 

 the trawl, since we know nothing of the composition of the stock of plaice in earlier 

 years, and but little of that of the present stock. Even as to the composition of the 

 landings of plaice by market classes we only possess exact information as to the last 

 twenty years, and material which can really be used for purposes of comparison is, as a 

 matter of fact, only to hand for the past ten years, since the beginning of better catch 

 statistics. In a period of so few years, however, casual phenomena and other factors 



