— 24 - 



size of trawled fish have been either too high or too low compared with the 

 Extra Small group. However the difference between our figures and the 

 reality can hardly be so considerable as to deprive these percentages of much 

 significance. 



Similar variations occur in the proportion between mature and 

 immature haddocks. Taking the same limit as before, viz: 28 cm., we get 

 the following values: 



Mature Haddocks (over 28 cm.) 



1903 



Number per hour 43 



Percentage of the whole catch 73 



While thus about three-fourths of the numbers in the 1903 and 

 1904 catches were mature, there was merely one-seventh mature in 

 the 1906 catch. 



II. Length and Age 



In the preceding chapter we have discussed the aggregate number of 

 haddock, partly throughout the whole extent of the North Sea where investigated 

 and partly within its different areas; and we have considered the changes from 

 year to year in this aggregate. We have further dealt with the distribution of this 

 total quantity into various groups of fish according to size, market-classification 

 and maturity. 



We will now analyse the haddock-supply in fuller detail, and begin by 

 studying the grouping observed in the catches made and the question whether 

 such a system of grouping can be employed with advantage for age-assessment. 

 Starting from the conclusions thus obtained we will proceed to examine the 

 variations found within the different areas of the North Sea, and especially 

 any variations in the occurrence of the different year-classes. 



1) Relation between length and age 



We have arranged in curves the measurements from each trawl where a 

 hundred or more individuals have been taken, giving in each case the length in 

 centimeters as abscissa and the quantity caught as ordinate. From among the 

 many curves thus obtained we have selected all such as showed any characteristic 

 grouping, and have made use of them to discuss the year-classes and age- 

 distribution. While engaged in this task I was able to avail myself of the 

 age-assessment by Damas after an examination of the scales, which the reader 

 will find described at length in his treatise. 



The advantage of this will be seen if we study the catches from area D, 

 round the Great Fisher Bank (see the chart, fig. i). In a haul by the "Michael 

 Sars" within this area on ist August 1906, the scales of nearly all the haddocks 

 were examined and the age-distribution thereby ascertained. The following table 

 gives the results of this examination by Damas: 



