_ II lî. IIKLUVND-HANSEN 



nierch- make use of the author's nauie. I am greatly iudebted to Prof. D'Arcy 

 Thompson and Dr. Damas for having got the opportunity of studying their papers 

 in manuscript; — to Mr. J. Skjkrdai. for his assistance with the calculations and 

 drawings; — and, above all, to Dr. Hjokt for his many suggestions. 



Haddock 



The greater part of the material treated here deals with the haddock, and 

 we shall therefore discuss this species first: since the methods which are the 

 same for both cod and haddock, will be easiest to describe in the case of the 

 latter, and the various questions with which we shall concern ourselves will 

 also be more adequately answered. 



I, Numbers 

 1) The average total numbers of individuals in the catches 



Reports on the catches of the research steamers show a total catch from the 

 autumn of 1902 till the autumn of 1906 amounting to 68733 haddocks for 1391 

 trawl-hours. This comes to an average of 49-4 haddock per trawl-hour, a 

 number which gives the mean of all the catches examined without 

 regard to either season or fishing locality, and which should express 

 approximately the average occurrence of haddocks over 15 — 20 cm. at all localities 

 in the North Sea where the steamers have carried on researches, and where it is 

 possible to use the trawl. It is however only a rough approximation to the real 

 conditions; since our researches, as mentioned in the introduction, were not 

 equally divided over the whole area and the different seasons. If anything it is 

 more likely to be too low rather than too high a number; as most of the catches 

 examined were from the southern or comparatively poorer portion of the North 

 Sea. The areas which are rich — so far as quantities go — have thus not been 

 given their due importance. On the other hand it probably expresses the average 

 "vital density" better than the numbers which could be obtained from calculations 

 based on the reports af market- trawlers, since these endeavour to avoid the "thinly 

 inhabited" areas. Further it embraces all the individuals caught by the trawl, 

 and thus includes all the small sizes which are not brought to market. We intend 

 to discuss more fully these average catches as compared with the statistics of the 

 catches brought to market, when we come to the subject of weight-conditions. 



The average catch per trawl-hour varies considerably with place and time. 

 For the different areas we have got the following figures, by means of 

 dividing the total number of individuals without regard to season or year by the 

 total number of trawl-hours: 



A B, CD EFGH J KLMO 

 average number per hour 127 129 20i 98 43 43 40 157 46 10 18 33 



