- 92 — 



In the following description we shall endeavour to outline the quantitative occurrence 

 of the older and adult stages, their growth and their migrations. 



The material discussed by Helland -Hansen contains 68,733 measurements of 

 haddock taken in the trawl by the research steamers "Huxley" and "Poseidon". In taking 

 these 68,733 haddock the two steamers have fished 1391 hours, which gives 49,4 haddock 

 per hour of fishing. Calculating how many kg. the above number represents, we obtain 

 11,9 kg. per hour of fishing. This number is distinctly smaller than that found by 

 D'Arcy Thompson. He gives, namely, no less than 68,9 kg. as the average catch 

 per hour of the Scottish steam trawlers in the North Sea, or almost seven times 

 as much as what the research steamers took per hour. This difference may be explained 

 in part in this way, that the steam trawlers preferably seek for the largest catches, 

 whereas the research steamers investigate as many different places as possible, partly 

 also, that D'Arcy Thompson's material comes exclusively from the part of the North 

 Sea lying north of 55°, whilst the research steamers mostly fished in the Southern 

 North Sea. 



It has been found indeed that the numbers in the different parts of the North 

 Sea varied very greatly in the northern and the southern areas. In the Northern North 

 Sea with depths over 30 fathoms the research steamers obtained an average number of 

 154 specimens per hour of fishing. The greatest catch — over 200 specimens — was 

 made on the Great Fisher Bank. On the coastal stretches off North England and east 

 of Flamborough Head in less than 30 fathoms depth, the average amounted to 43 had- 

 dock per hour of fishing, about the same as the average catch for the whole North Sea. 

 In the most southerly and easterly parts, on the coasts of South England, Holland, Ger- 

 many and Denmark with depths of less than 20 fathoms the average was only 13 per 

 hour. As a specially large number of hours was taken up in fishing this southern part, 

 for the reason that the plaice fisheries here were being investigated, it can be understood 

 that the average number must be very different from the catches of the steam trawlers 

 in the Northern North Sea'. 



In consequence of this, great care has to be used in drawing general conclusions 

 from the catches of the experimental steamers, and it must especially be remembered 

 that they can say but little regarding the Northern North Sea. 



We may now consider the material such as it is, in order later to discuss what it 

 may show us. 



On the accompanying figure (fig. 27) the dotted line^ indicates the average number 

 at each size in centimeters per hour of fishing, without regard to time or place; 

 the other continuous line denotes in the same way the average weight at each size 

 in kg. per hour of fishing. 



The number curve shows that no specimens under 15 cm. were taken and that 

 the numbers increase up to 24 cm. This comes from the peculiar nature of the trawl, 

 which permits all the smaller specimens to escape through its meshes; experiments made 



1 In the information given by Henking on the average catch per day in the Southern and Northern 

 North Sea we also find a similar contrast between the regions discussed here. 



2 With regard to the details in these and the following curves reference should be made to the special 

 papers concerned. 



