174 A CENSUS OF THE SEA [PART II 



ability. Consider the quantities of fish landed in one year from 

 the North Sea. In 1904 there were^:— 



Cod 70,554,148 kilogrammes 



Haddock 166,391,042 



Plaice 58,461,073 



Dabs 9,551,591 „ 



Flounders 1,982,415 



Dabs and flounders are probably much underestimated. 



Long rough dabs are apparently incorrectly estimated. 



Now the relation of the weights and lengths of these fishes is 

 known, and also the average lengths of the fishes usually landed. 

 " Equivalents " are given in the Bulletin Statistique which enable 

 one to convert quantities of fish into numbers of individuals. The 

 conversion is, in some cases, only a roughly approximate one, but 

 in other cases it can be carried out very exactly. D'Arcy Thompson 

 first shewed what the relation of weight and length was in the case 

 of the plaice ; and Heincke and Henking'^ have given a formula for 

 this fish which is very convenient. It is 



. , ,. ^ lens^th"' (in cms.) ^ ^ 



weight (m grams) = — - — zr^ x constant. 



The constant varies from 0*8 to I'O. It depends on the con- 

 dition of the fish, which varies with the season of the year. 



The numbers of fishes, of the five species mentioned, landed in 

 1904 from the North Sea were : — 



Cod 65,192,000 



Haddock 274,540,000 



Plaice 229,160,000 



Dabs 37,279,000 



Flounders 7,760,000 



Total... 613,931,000 



Basing our calculation upon Hensen and Apstein's results we 

 found that about 9000 millions of these five fishes might have 



1 The figures for 1895 cannot accurately be ascertained. Those for 1904 

 are taken from the Bulletin Statistique of the International Fishery Council, 

 Vol. I. 1906. 



2 In " Schollen u. Schollen Fischerei, S. 0. Nordsee," in Beteiligung Deutsch- 

 land Internat. Meeresforschungen, iv. — v. Jahresber. deutsch. Wiss. Comm. Berlin, 

 1907. 



