— 3 — B. HELIvAND-HANSEN 



subjected to statistical consideration, since the different kinds of measurements are 

 eitlier too few or else too purel)- local or desultory. To get the necessary uniformity 

 therefore I was obliged to confine myself to the two species haddock and cod. 



The different countries have sent us much material relating to these two 

 species, so that we could draw ujd long tables of figures for the North Sea, the 

 Norse Coast, Iceland and other localities. And no doubt a comparison between 

 these different large areas would be extremely interesting. Still on many points 

 considerable difficulties would arise. The material does not always show the 

 same character with regard to time: and this is to a great extent owing to the 

 great variations in the occurrence of the two species at different parts of North 

 Europe. Thus it is very frequently impossible to accord to the extremely hap- 

 hazard occurrence of either the Lofoten or Finmark cod a statistical treatment 

 such as we employ for the cod of the North Sea. In manj' important particulars 

 too it is difficult to compare these extensive and dissimilar areas owing to the 

 differing methods of capture in vogue. We cannot for instance institute com- 

 parisons for either the numbers or the age-distribution in the catches: seeing that 

 in some localities they have been made with the trawl, in others with the line 

 and with hooks and bait of different size and character, and in others again with 

 traps. I have accordingly confined myself to merely considering catches made 

 with the trawl. 



We do not possess any details of numbers or length-measurements for catches 

 with the trawl on the Norse coast, and there is but fragmentary material from 

 Iceland. Accordingly we have deemed it prudent to restrict ourselves to the 

 North Sea, as it is the area from which we have the largest uniform material. 

 We were the more induced to do so because in respect to both haddock and cod 

 the North Sea is of most interest to the Commission. 



Our limiting ourselves to haddock and cod caught with the trawl in the 

 North Sea is moreover largely due to the fact that the present work is above all 

 else a study of the methods. To become thoroughly acquainted with the 

 aggregate of cod and haddock, its composition and fluctuations, in such large 

 and heterogeneous waters as the North Sea, requires a far larger amount of 

 material than what the Commission has been able to procure. We must make it 

 clear therefore from the very beginning that we are not now aiming at establishing 

 the actual number or density of the individuals belonging to the two species in 

 the North Sea or its component parts; and that so far as either numbers or 

 bulk are concerned we are perfectly well aware that the proportion between the 

 different areas, periods and size-groups cannot be determined with sufficient 

 certainty. Our material suffices merely to furnish an example of a plan of work 

 calculated to try to solve such problems. Undoubtedly some momentous facts 

 may be claimed as certain — e. g. the want of haddock spawned in 1903 — but 

 our results ought principally to be regarded as an attempt to solve by means of 

 statistics the biological problems most likely to be of importance to the fishing 

 industry. 



The material we are about to consider was chiefly collected by the trawls of 

 the English and German research-steamers "Huxley" and "Poseidon". A 90-foot 



