- 58- 



2 years old are much more numerous in the trawl-catches from the North Sea 

 than any other year-classes. The number is constantly decreasing with the 

 advancing age. The weight of the year-classes is however increasing; for 

 instance, the total amount of individuals 5 years old weigh more than all the 

 many individuals of 2 years. More than half of the number of cod caught by 

 the research steamers have been less than 3 years old, and more than half of the 

 weight is due to relatively few individuals older than 6 years. We see that in 

 the catches individuals of an approximate age of 



less than 2 years (under 



30 cm.) formed 36 % of the total number and 3 % of the total weight 



2—5 years (30—60) ... — 47 % — — 27 % — — 



over 5 years (over 60 cm.) — ^7% — — 7°% — — 



It was pointed out above (p. 51) that the catches made by the research 

 steamers during the different years displayed small variations in the number of 

 cod^ but rather great variations in the number of unmarketable cod and codling. 

 As weights are influenced by the number of the large, mature cod to a 

 much greater extent than by the groups of smaller individuals we find, that the 

 average total weights for the different }'ears 1903 to 1906 do not vary very much. 

 I shall not go into further details as to these variations because our material 

 is too scanty; it may only be mentioned that, during those years, the greatest 

 weight per trawl-hour was found in 1903, in accordance with the statistics treated 

 by D'Arcy Thompson. 



Concluding Remarks 



We began by stating in our introductory remarks that our treatise must 

 chiefly be regarded as a study of methods; for this the material gathered by the 

 Research Steamers has been of great value. It has in point of fact enabled us 

 to form an opinion of what we might hope to attain by more comprehensive 

 researches in the future. It will in all probability be possible for us to set about 

 the arduous but at the same time hopeful task of giving a satisfactory synopsis 

 of the occurrence of some of the most important food-fishes at a given season: a 

 synopsis of the relative numbers and weights of individuals belonging to the 

 different sizes and ages. From continued investigations it will be possible for 

 us to follow the variations in the whole aggregate and its essential parts: varia- 

 tions which are in no way connected with fisheries (fluctuations in the accessions 

 of new individuals that are due to birth or immigration, or irregular diminutions 

 due to emigration and death) as well as such changes in the aggregate as may 

 be ascribed to the intervention of man. We might even go further: it is not 

 unreasonable to anticipate that we should be able to forecast the yield of our 

 fisheries. 



I have here merely treated the material furnished by the Research Steamers 

 as a means of attempting to answer some of these questions in connection with 

 the North Sea and two of the most important species. Even within these limits 

 however there are still further limitations, as certain portions of the North Sea 

 have not been available for study. Thus our investigations have been entirely 



