— 28 — 



ginning of June, it is between 272 and 5 cm. in the four months from June to 

 October. 



It is equally clear from these observations, and becomes clearer still if we 

 consider the numeroiis scale-investigations carried out by Damas in other areas of 

 the North Sea, that the yearly growth is constantly on the decrease and that conse- 

 quently, where length is concerned, the older groups are bound to overlap because 

 the variations of length within the same year-class are considerable. 



Now if we compare these figures giving the average length of the year- 

 classes with D'Arcy Thompson's statement as to the length of the various market 

 sizes (see page 17), we will see that these latter correspond in the main with the 

 following age-groups: — 



Market-Groups Age-Groups 



Extra Small... I— II 



Small II-III 



Medium Ill— IV 



Large IV and over 



The results obtained from measurements taken in the area round the Great 

 Fisher Bank would seem to imply that we can decide the age-groups quite easily 

 and safely in the case of haddocks by merely measuring their length. However 

 the area we have selected was especially favoured in this respect; and it will be 

 found that in other areas there are such great variations in the average length 

 of the length-groups that it is often imsafe to draw any conclusions as to age 

 from length-groups, however apparent they may seem. 



To illustrate this we will take as an instance the measurements obtained 



from area G, between Flamborough Head and the Dogger-Bank (at depths of 



20 — 30 fathoms). We have a large number of curves from this area also, which 



show very well-defined groupings. The average len,gth of these groups has been 



indicated by stars in fig. 15. They arrange themselves as systematically as was 



to be expected, and the growth-curve (the broken line in the figure) shows the 



same rhythmical growth that we found in the Great Fisher Bank area. For the 



same area, G, Damas has given the age-assessment of two catches made at the 



beginning of September 1906. The results will be found in the following table, 



together with the values denoting length as indicated by the growth-curve 



in fig. 15: — 



Average length at the beginning of September 



Group As per scale-test As per growth-curve Difference 



I 24'9 cm. 22"o cm. 2'9 cm. 



II . : . . 30-5 - 26-2 — 4-3 - 



III.... 347 - 31-4 - 3-3 - 



It will be seen that the agreement between the scale-test and the size- 

 measurement is but slight. As a matter of fact the values for the various year- 

 groups as per growth-curve correspond most nearly with the values for the 

 preceding year-group as per scale-test. Thus the III group is given as 31-4 cm. 



