-46- 



The average total number per trawl-hour in the different years was: — 



in 1903 4'5 individuals per trawl-hour 



1904 4-4 — — 



1905 57 — — 



1906 5-1 — — 



These variations are very slight compared with those noticed in the case of 

 haddock, and we may say therefore that the "movement" of the cod- 

 aggregate during 1903 — 6 was relatively small. The most outstanding 

 difference — roughly twenty per cent over the average value 4-8 — will 

 be seen to have occurred in 1905, whereas in the haddock-aggregate the 

 variations went to nearly fifty per cent. No general decrease in the number of 

 cod was to be noticed in the localities investigated during the course of the short 

 period under review. 



We can further calculate by means of the material here treated what was 

 the average number of cod within the different groups of areas during the time 

 that our investigations took place. If we make use of the same grouping arrange- 

 ment that we previously employed for haddock (page 12) we will get the following 

 average values for the years 1903 — 6 (1902 excluded): — 



Area-groups Number of individuals Number of hours Individuals per hour 

 Northerly 1651 227 7-3 



Mid 6600 919 7-2 



Southerly 2914 1191 2-4 



These figures are no sufficient indication of the general conditions: for, as 

 previously mentioned, our investigations were not evenly distributed over the 

 different areas at all seasons of the year. However it is not unreasonable to 

 conclude that — contrary to what we showed was the case with haddock — 

 there is no essential difference as regards average numbers between the area- 

 groups which we have designated Northerly and Mid respectively. On the other 

 hand the number is distinctly smaller in the shallow Southerly and Westerly 

 portions of the North Sea (areas L, and M). 



It would be useless to try and employ our material for elaborate calculations. 

 We have insufficient observations to enable us to show the average-number of 

 cod within each group of areas for every year; and we cannot therefore trace the 

 variations from one year to another within the different portions of these waters. 

 We can get some idea of their range from the statistics of the weights of 

 fish landed which Fulton in the XXIst Report Scot. Fish. Board (1902) and 

 D'Arcy Thompson (for the years 1901 — 6) have treated. I will confine myself to 

 referring to what they have written. 



2) The average numbers of the different cod sizes 



Fig. 31 shows the average distribution of the different sizes of cod. The 

 average-numbers per trawl-hour for individuals of the different centimeter-sizes 



