92 



DISCOVERY REPORTS 



COMPARISON OF THE COMPOSITION OF THE CATCHES 

 OF THE DIFFERENT NETS 



Before passing to a description of the distribution of the different organisms as re- 

 vealed by the N 70 V, N 70 H and N 100 H nets it may be convenient to put on record 

 here the relative composition of the catches of the three nets. The figures about to be 

 given are based on catches taken in the top 250 m. of water only. Such differences 

 as there are between the composition of the catches of the N 70 net used vertically and 

 horizontally may be attributed largely to the fact that whereas the N 70 V net was 

 always used from 250 m. to the surface (when soundings allowed of it), the N 70 H nets 

 were usually confined to the top 150 m. Both Protozoa and Polychaeta occurred in 

 larger numbers between 250 and 100 m. than between 100 m. and the surface, and so 

 form a higher percentage of the catch of the N 70 V than of the N 70 H ; the Copepod 

 Drepanopus on the other hand is confined to the upper layers and to regions near the 

 coast, so that it figures as a higher percentage in the N 70 H nets. The difference be- 

 tween the catches of the N 100 H and the N 70 nets is of course due to the larger mesh 

 of the former net, which was specially designed to capture the larger forms and eliminate 

 the smaller forms sampled by the other nets. The diatoms have been excluded from 

 these calculations, the percentages being based on the numbers of zooplankton organisms 

 taken throughout the survey. 



If we divide the total zooplankton organisms into Copepoda and other organisms we 

 get the following percentages of the catch : 



N70V N70H N100H 



N70V N70H N100H 



Considering only the organisms other than the Copepoda we get the following 

 percentages : 



