n6 



DISCOVERY REPORTS 



Little reliance can be placed on the single stations (WS 311, etc.) for reasons given 

 on p. 71, but it will be seen that they support the suggestion that the plankton increases 

 rapidly about the middle of November. Apart from this no reliance can be placed on the 

 curve, for the reason that the plotted points are derived from different seasons, and the 

 volume of plankton production in these seasons may have been different. 



1X9-30 



MONTHS 



Fig. 31. Quantities of plankton at different times of year around South Georgia. 

 Figures on the vertical scale represent numbers of hundreds of organisms. 



If we consider the charts of the four principal surveys in the order of the months in 

 which they were taken, i.e. November 1930-1, December-January 1928-9, January- 

 February 1929-30, and February-March 1927-8, we see that in the earliest (Fig. 29) 

 the richest plankton was mostly grouped to the north of South Georgia, while in the 

 latest (Fig. 24) it was concentrated to the south. In the January-February survey 

 (Fig. 28) it was very rich almost everywhere, but in the December-January survey 

 (Fig. 26) the only rich plankton was a patch to the south-east. It seems possible that 

 there is a tendency for the concentrated plankton to occupy the northern part of the 

 whaling area in the early part of the season, and later to shift down to the south side, 

 and that in 1928-9 the shift for some reason took place unusually early, resulting in the 

 reduction in the average number of organisms per haul in that survey. With the available 

 data we cannot be certain that this shift takes place : it can only be said that there is 

 some evidence for it. 



Drake Passage and Scotia Sea 



Figs. 32-9 are drawn on exactly the same principle as Fig. 23, but they show the 

 amount of plankton taken at all stations in the Scotia Sea, and each chart shows the 

 stations taken within a single short period. No certain conclusions can at present be 

 drawn from the figures shown, but it will be seen that, while at all times there is a scarce 

 plankton in the vicinity of the South Orkney and South Shetland Islands, the quantity 

 of plankton varies greatly in other places. 



