- 45 



B. HELLAND-HANSEN 



the haddock aggregate during recent years. In actual fact there were far more 

 individuals in 1906 than in any of the three preceding years. But it will probably 

 be a year or two before the large quantity observed in 1906 has any substantial 

 influence upon the weights of the whole haddock aggregate or its higher groups. 



Cod 



In the areas which we are here considering cod are far from being found 

 in the same quantity as haddock are. Although in their case we have full 

 details and measurements for a far larger number of trawl-hours, the total 

 number of individuals is hardly a sixth of the number recorded for haddock. 

 Our material is therefore too small for us to be able to contribute anything 

 of value towards many of the questions which were of significance in our 

 study of the haddock-returns. It will be extremely difficult to trace many of the 

 variations in the North Sea; and when we come to the question of age-assessment 

 by means of length-measurements we must confess to partial failure hitherto. I 

 shall endeavour however in what follows to continue on similar lines to the 

 previous discussion; a comparison of the two species will in some cases guide us 

 towards interesting conclusions. 



I. Numbers 



1) The average total numbers of individuals in the catches 

 The returns of the research steamers show a total of 11440 cod; which, if 

 we include negative results as well, were taken in 2387 trawl-hours. From these 

 two totals we get an average catch of 4-8 cod per trawl-hour irrespective of 

 area or time: a number which expresses roughly the average density of cod per 

 stretch (i. e. the extent of ground swept by a 90-foot trawl in an hour) in those 

 portions of the North Sea where the research steamers were at work and where 

 it was possible to trawl. 



The average we thus get corresponds with the figure recorded for haddock, 

 viz: 49-4. Here again we must point out that the catches were not equally 

 distributed either over the whole of the waters or over all the years and seasons: 

 while it must be further noted that the number 4-8 cannot be regarded as a true 

 index of the real quantity of cod existing throughout the whole of the waters, 

 also owing to the fact that parts of the North Sea where it was impossible to 

 trawl, but where cod may be found in considerable quantities, had to be absolutely 

 left out of account. Cod as is well known seem to prefer hard bottom where 

 trawling is impracticable. 



Thus in the localities examined the average number of cod is merely a tenth 

 of the number recorded for haddock, and they would seem accordingly to 

 constitute a much smaller element in the "population" of the North Sea. 



