COPEPODA i 4 i 



We have said that this large Copepod R. gigas was taken in large numbers by the 

 N ioo H nets, which being of a wider mesh than the N 70 V nets let through nearly all 

 the other Copepoda (except notably Parenchaeta antarctica and Calanus propinquus). 

 Because they formed quite a prominent feature of these N 100 H samples, along with 

 the Euphausiacea, Amphipoda and other members of the macroplankton, we have 

 plotted the results of the N 100 H analyses in Fig. 67 in the same manner as the other 

 N 100 H results, i.e. on the basis of the numbers caught in three nets each towed fori mile 

 (the nets being fished at approximately 0-5, 50 and 100 m., for exact depths see table in 

 Appendix II). This figure enables the numbers of RJiincalanus to be compared at a glance 

 with the numbers of the other members of the macroplankton. On the other hand, it also 

 forms a connecting link in the matter of numbers with the smaller members of the 

 zooplankton as sampled vertically by the N 70 V nets, for this species R. gigas is sampled 

 by both nets. We see how much more numerous many of the smaller Copepoda are than 

 the species of the macroplankton. The numbers of Rhiticalanus seem large when taken 

 by the N 100 H nets, but when sampled by the N 70 V nets and plotted in the same 

 manner as other smaller N 70 V specimens we see that they are present in relatively 

 small numbers. At first sight, when we compare Figs. 66 and 67, the results appear 

 quite contradictory, yet actually this is not so. To begin with, Fig. 67 is showing the 

 sampling of three horizontal layers lying in the top 100 m. or so ; Fig. 66 is showing the 

 complete vertical sampling of the top 250 m. The upper N 70 V nets in Fig. 66 are 

 hauled through in 50 m. of water (50-0, and 100-50 m.), and the lower ones through 

 150 m. (250-100 m.); the number given represents the whole column, being shown as 

 the average number per 50 m. In Fig. 67 the numbers given represent the numbers 

 taken in three miles' tow (i.e. three nets for one mile each), or in 5557*8 m. Now the area 

 of the net opening of the N 100 H net is twice that of the N 70 V net, and further it is 

 of wider mesh, so that the amount of water filtered is considerably greater than that of 

 the N 70 V net. However, neglecting the matter of filtration and considering only the 

 size of net and the length of tow, we see that to compare the numbers shown in the 

 N 100 H net figures with the numbers shown in the N 70 V net figures, we must divide 

 them by approximately 222. Then it must be realized that the N 70 V figures show the 

 average for a vertical column of water which has been sampled all the way up, whereas 

 the N 100 H figures show the numbers taken in three horizontal layers across the upper 

 part of this column and for a mile beyond. 



Its seasonal distribution may be gauged, admittedly on slender material, by com- 

 paring the C lines taken in November 1926, December 1926, March 1926, and May 

 1927, when the average numbers per 50 m. haul with the N 70 V net from the five 

 stations on the line were 18, 57, 71 and 20 for the four seasons respectively, showing an 

 increase towards late summer and a falling off on the approach of winter. 



The vertical distribution round South Georgia is shown in Fig. 68, and that approach- 

 ing South Georgia from the north-east in February 1926, and between South Georgia 

 and the Falkland Islands in Fig. 69. It was most abundant between 50 and 250 m. 

 and was not taken at levels below 750 m. Its mean vertical distribution at deep-water 

 stations is shown in Fig. 55. It did not appear to exhibit any vertical diurnal migration. 



DXI If J 



