— 55 ~ B. HRLLAND-HANSRN 



case of the o-group. Thus cod in their first year of life can attain a size of 20 cm. 

 in the southern parts of the North Sea, while in the Skagerack they have been 

 found as small as 4 — 5 cm. A corresponding even if considerably smaller difference 

 in rate of growth per year will probably also occur in the case of the older groups. 



It is clear then that the various groups extend over no inconsiderable portion 

 of the length-scale and that they overlap to such an extent as to be indistinguishable. 



Our material quite corroborates what Fulton says in XXI Scottish Fishery 

 Board's Report (part III, page 59): "Compared with many other fishes, the cod at 

 all stages of its life appears normally to be a widely-dispersed fish. I have been 

 struck with this in examining the hauls ou the trawlers: a few, and only a few, 

 cod or codlings being generally taken in each drag. During the greater part of 

 the year they are dispersed and scattered." 



Heincke again comes to the following conclusion from his investigations in 

 the North Sea (Rap. et pr. verb. Ill): "The cod appears here as a stationary fish, 

 whose developmental stages from the egg to the spawning fish are all pa.ssed 

 through within the same region; to such a degree, indeed, that all the stages are 

 found intermingled at the most different places, without anywhere or at any time 

 showing a graded distribution according to age and depth." 



The groups which the smaller sizes (codling) would appear to indicate are, 

 as previously said, indistinct owing to the variations within each year-group being 

 so considerable. If to this we add the wanderings between areas which may lie 

 near one another but which all the same show a very different rate of growth, 

 the variations become greater still and the groups even more indistinguishable. 

 'These wanderings take place to a certain extent amongst all sizes and to a 

 marked degree amongst the mature fish (D'Arcy Thompson, Heincke). 



Thus in the case of cod the material of the Research Steamers 

 cannot be considered sufficiently reliable for assorting the 

 different year-groups and it will always remain doubtful whether length- 

 measurements could properly elucidate the age-groups and growth of cod in the 

 North Sea, even with a considerably larger material. 



In order to find the age of cod it is, therefore, necessary to use other and 

 more direct methods. Damas has found that the scales give a means of determining 

 the age of cod similarly to the haddock. He has by this method made some 

 determinations of a trawl-catch from the North Sea, North of Doggerbank, in 

 September 1906. He got the following results: 



The very great variations of the length of individuals belonging to the same 

 age-group will be especially noticeable. If we employ these determinations we 

 shall find that, upon the whole, unmarketable comprise individuals 

 which are less than 2 years old, codling such between 2 and 5 years 



