— 32 — 



tedious, because the difficulties indicated are of the greatest importance, as far as 

 method is concerned, and have demanded our utmost attention while engaged in 

 investigating our material. 



2) Variations in the presence of the different year-classes 



If we study the various catches at 

 different seasons and localities we will 

 find great variations in the occurrence of 

 the several groups. Sometimes there is 

 practically only one size-group in the 

 whole catch, while at other times there 

 may be many. Even within the same area 

 and at the same season variations will 

 occur, when the various groups are not 

 equally distributed throughout its entire 

 extent Again there may be differences 

 between the areas, and a group found in 

 one area may be wanting in another. 

 Finally there may be variations in the 

 different years. 



Figs. 22 — 23 show two typical curves 

 from section G, one for October 1905 and 

 the other for October 1906. Some figures 

 have been inserted to denote the different 

 year-classes (year of spawning). In the catch 

 made in 1905 the 1904 year-class (group I) 

 is very prominent, and there was only an 

 odd individual of the other year-classes : the 

 II group (spawned in 1903) were completely 

 absent. In fig. 22 we find both group I and 

 group II (spawned in 1905 and 1904) well 

 represented. Many instances of similar 

 conditions will be found in our material. 

 In the catches from 1905 group II 

 is generally very poorly repre- 

 sented, and is often practically 

 absent; though the same group is 

 present in nearly all the catches 

 from 1906. This serves to show that a 

 particular year-class may sometimes be 

 much less in evidence in the catches than 

 it normally ought to be. 

 Fig. 22-23. Two catches of haddock; both ^^ ^^^^ ^^.^ question further oue 



from the area off the Enghsh coast, and both ■' i l j 



for the month of October; the upper in the Can construct curves - as has been done 

 year 1905 and the lower in 1906. in figs. 24—27 — for the averagecatches 



190^ 



1905 



