_ 57 — B. HELLAND-HANSEN 



of individuals. As nmch as ',, of the individuals formed therefore only about '/30 

 of the weight and were without any value at all. 



The average total weight of marketable cod was 5-9 kg. per trawl-hour. 

 D'Arcy Thompson has found that the Scotch trawlers on an average (1901 — 6) 

 caught more than 3 times as much, viz. 19 kg., in the Northern part of the North 

 Sea. This difference is not so considerable as was the case with the haddock. 

 Of haddock the Aberdeen trawlers caught 6 — 7 times as much as the research 

 steamers (p. 39). The different relations of cod and haddock may be explained by 

 assuming that the cod were more evenly distributed over the North Sea than the 

 haddock at the time when the research steamers were at work. It is plainly 

 shown by D'Arcy Thompson that there is a much greater difference in the 

 occurrence of haddock between the Northern part of the North Sea and the central 

 one than is the case with cod. Haddocks are found much more abundantly in 

 the Northern North Sea than further to the South; we learnt, that there was 

 much more of them in the Northerly group of areas than in the Mid group, 

 while the average number of cod was almost the same in these area-groups. 



Codling constituted a little more than ^4 of the average total 

 weight (27 %)) while the number of individuals belonging to this 

 group formed 72 (50 %) of the total number. Cod constituted as much 

 as 70% of the weight but only 17 % of the number. D'Arcy Thompson's 

 statistics show an average catch of 7 kg. of codling and 12 kg. of cod per trawl- 

 hour, the percentages of the total weight of marketable being 37 % and 63 % 

 respectively. The research steamers have thus caught more cod in proportion 

 to codling than the Aberdeen trawlers have. 



The distribution of the average weight according to the length of the 

 individuals is demonstrated by the curve of weight in fig. 31 (the complete line). 

 While the curve of number shows a maximum at 24 — 25 cm. the other curve has 

 a maximum at more than 90 cm. The median lies at about 35 cm. as far as 

 numbers are concerned, as to the weight however at more than 75 centimeters, 

 i. e. half the weight is formed by individuals larger than 75 cm. The particulars 

 are seen from the following table showing the number and weight of different 

 10 cm.-groups: 



Length Number Weight 



Total 4-8 100 6-1 100 



On comparing these figures with the table given above, showing the 

 mean length of the different year-classes, we see, that the individuals i and 



8 



