— 14 — 



year is much greater than in the other groups, while the variations there are 

 particularly large. 



It will be noticed in this last table that the rise from 1904 to 1905 does not 

 take place in the Northerly group of areas, though it is very marked in the 

 others. This seems in harmony with D'Arcy Thompson's results. A maximum of 

 Small Haddocks occurs in the northern North Sea during the spring, in the Mid 

 group of areas during the autumn and winter, and in the Southerly group during 

 summer and winter. It is probable therefore that the effect observed in the south 

 during the autumn of 1904 is not fully felt in the Northerly group of areas till 

 the beginning of 1905. 



We must ever bear in mind that the numbers are always mainly dependent 

 on the small individuals. We shall see later that more than half of the total 



IV 



1902 



n m' IV I 



1903 



Fig- 3 



aggregate are of the ages of one and two years, and that it is therefore these 

 young haddocks born one or two years previously which are most in evidence. 

 When we see therefore from the average figures for the different years that there 

 were very few young haddocks in the North Sea in 1904 compared with what 

 there were in 1906, we may conclude that relatively there were few individuals 

 in the North Sea born in 1902, and extremely few born in 1903 in our catches; 

 whereas in 1904 there were many. These conclusions quite justify the results 

 we shall afterwards arrive at in a different manner. 



The different year-classes will also be much in evidence when we come to 

 discuss conditions of weight. A year or two after birth there must be an advance 

 in weight for both Extra Smalls and Smalls, and later on the weights of the 

 larger market-sizes will also be affected. That there is a connection of this 

 nature can be easily shown (see later on). 



The great variations from year to year render it necessary to have a long 

 series of observations before we can obtain even a tolerably reliable mean niimber 

 to express the "density of haddock" in the North Sea. The number previously 

 given, 49-4 haddock per trawl-hour, merely represents the average for four years, 

 and for this reason alone forfeits all claim to be regarded as entirely satisfactory. 



Fig. 3 shows the results of an attempt to calculate according to seasons the 

 average numbers of haddock in the different years throughout the whole North 

 Sea examined. It is quite clear that the numbers were extremely small in 1904 



