-56- 



and the mature cod individuals over 5 years old. As to the relative 

 occurrence of the different year-groups see subsequently, under "Weight". 



D'Arcy Thompson had a great many length-measurements made of cod, landed 

 at the Aberdeen market. The cod had been sorted in boxes according to the 

 ordinary market classification before being measured. These measurements seem 

 to indicate considerable differences in the average length of the size-group cod 

 from different localities and at different seasons. Fig. 35 exhibits an example of 

 such differences. One of the curves is based upon some catches from the neigh- 

 bourhood of Shetland, between 60° and 61° N. Lat, in March and April, 1905; the 

 curve shows a maximum at about 85 cm. The other one, from the North Sea 

 off the East coast of Scotland in April 1904, shows 2 maxima at considerably 

 greater lengths. I have tried to calculate the mean length of the cod measured 

 in this way. As this material is also rather dispersed as to area and time, it can 

 not give much to elucidate the differences in growth. It seems however to 

 indicate with sufficient certainty, that the average length in the northernmost 

 part of the North Sea in spring time is several centimeters less than the average 

 length further to the South. 



III. Weight 



The number of cod has been converted into weight by means of Fulton's. 

 tables of the average weight of the different lengths of the individuals in the 

 same way as used for the haddock. These calculations cannot be regarded as 

 being in any way accurate, and they cannot be used for studying any minute 

 details. 



As a result of these calculations we have found, that the total average weight 

 of cod caught by the research-steamers was 6-i kg per hour's trawling, 

 corresponding to the average number of 4-8 individuals. The average weight 

 per individual was therefore about 1-3 kg., this being 5—6 times larger than the 

 average weight of the haddock (0-23 kg.). 



The weights of the different groups according to the market-classification 

 were: 



Weight per hour's trawling 



kg. per centage 

 Unmarketable (under 29 cm.) ... 0-2 3 



Codling (29 — 60 cm.) i-6 27 



Cod (over 60 cm.) 4-3 70 



Total. . . 6-1 100 



The average weight of unmarketable was quite insignificant, 

 this part of the catch forming no more than 3 per cent of the total 

 weight. The same part constituted no less than 33 per cent of the total number 



