- 98 - 



Similarly the "unmarketable" corresponds to the I-group ; perhaps the largest speci- 

 mens of the 0-group are added to this in winter. 



Whilst it was easy to make out an agreement in the material from the Great Fisher 

 Bank between the age determinations and the groups derived from the measurements, at 

 least in the case of the lower sizes, the material from other areas has presented greater 

 difficulties. Helland-Hansen shows this in detail; he points out that in many cases it is 

 impossible to determine from the measurements, whether two groups are of different ages 

 or belong to the same year. This may be explained as follows, that the growth of the 

 haddock is quite different in the different parts of the North Sea, as appears also from 

 fig. 29 on which growth-curves from two different areas are represented. It is possible 

 nevertheless by means of the age determinations which have been made, to overcome 

 these difficulties to some extent and to determine some facts, the principal of which may 

 be mentioned here. 



During the preliminary work the entire material collected was subjected to graphic treat- 

 ment, each haul being taken separately or the hauls made during a definite period or 

 within a limited area were grouped together if they showed distinct size-groups, especi- 

 ally of the smaller sizes. These correspond essentially to the age-groups, and wherever 

 it was possible they were marked by the number of the year in which the group was 

 born (year of spawning); for example the Il-group taken in the year 1906 was marked 

 1904. A comparison of the different hauls then showed, that quite different age- 

 groups could appear on one and the same bank at different seasons and 

 in the different years. 



Fig. 30 represents two hauls, both from the English coast and both from October, 

 but the one is from the year 1905, the other from 1906. In the October 1905 haul 

 (uppermost in the figure) we see only a large, well-marked group with the year's number 

 1904; in the October 1906 haul we have 2 groups dated 1904 and 1905. Thus, in the 

 year 1905 it was the year-group 1904 of haddock which exclusively or mainly occurred 

 in the trawl hauls on the English coast, whereas in October 1906 we have the same 

 year's group as before and also a new I-group from 1905. 



This observation led to an extensive comparison of the curves for all the areas and 

 years, with the result, as is shown by Helland-Hansen in detail and in various ways, 

 that in all the areas of the North Sea investigated by the research steamers the Il-group 

 (spawned in 1903) was very sparingly represented in the 1905 hauls, whilst the group 

 spawned in 1904 was extremely numerous, both in the 1905 hauls, where it constituted 

 the I-group, and in the 1906 hauls where it formed the Il-group. A single year's group 

 may thus give rise to a similar state of things everywhere within so large a region as 

 that investigated by the research steamers. 



This appears best of all and most clearly from a chronological arrangement of the 

 hauls, in which these are placed under one another and are thus easily compared. Fig. 31 

 shows the area of the Great Fisher Bank; we notice here how the groups spawned 

 in 1902 and especially 1903 are but weakly represent ed in all the hauls. 



