336 ■ DISCOVERY REPORTS 



evident, in view of its age, that it was spawned considerably later than the population on 

 the Antarctic side of the convergence, but perhaps about the same time as that sampled 

 at St. 825 at the end of January. However, at both these stations (828 and 829) on the 

 sub-Antarctic side of the convergence the catches are too small to allow conclusions to 

 be drawn from them ; but if this is the correct explanation of the disappearance of the 

 Rhmcalanus population from sub-Antarctic water at the end of the summer, it must be 

 supposed that the over-wintered stock is carried northward across the convergence by 

 Antarctic surface water on reaching the upper layers in the early spring. This would 

 account for the large catches of Rhincalaniis in sub-Antarctic water early in the year 

 but one must suppose that most of the population in this water dies out without 

 spawning during the summer. 



At the two stations (830 and 831) on the Antarctic side of the convergence, we find 

 that the catches were enormously greater than on the sub-Antarctic side, though some- 

 what reduced compared with the same locality in November (Figs. 8, 10). Two distinct 

 stocks are found here also (Fig. 24), one consisting mainly of stages iv, v and vi, at the 

 warmer station (830, 4-15° C), and a younger stock consisting of stages iii and iv at 

 the colder station (831, 274° C). It may be suggested that the stock at St. 830, just on 

 the Antarctic side of the convergence, was spawned in the eastern Drake Passage in 

 water with an average temperature higher than i -0° C. but lower than 4-0° C. (see Fig. 5). 

 The stock at St. 831 must also have been spawned in the eastern Drake Passage, but 

 in water with a temperature lower than i-o° C. (see Fig. 5). Its age indicates that it 

 was spawned later than the stock in the warmer water near the convergence (St. 830), 

 so that again spawning has been delayed in the water of lower temperature. It is seen 

 that the stock in the Bellingshausen Sea current immediately west of South Georgia 

 in the latter half of February consisted mainly of stages iii and iv (Fig. 24; St. 831), 

 so that it was not much farther advanced in age than the population sampled in the 

 same water in the South Atlantic east of South Georgia during the first half of January 

 (Fig. 21 ; Sts. 796, 802 and 803). Near the convergence, between the Falklands 

 and South Georgia (St. 830), the population is older, mainly in stages iv and v, but 

 still younger than might be expected if it had been spawned at the same time as the 

 stock east of South Georgia earlier in the season. It is evident then that the spawning 

 in the eastern Drake Passage, where the population at Sts. 830 and 831 originated, 

 must have taken place considerably later in the season than the spawning in the 

 South Georgia area. It occurred earlier in the warmer eastern Drake Passage water, 

 however, than in the colder water, as may be seen from the difl^erence in the ages of 

 the populations sampled at the two stations 830 and 831. 



SUMMARY, FALKLAND SECTOR, SEASON 1931-2 



1. Rhincalanus gigas passes the winter generally in copepodite stages iv and v, as 

 has been found for species in the northern hemisphere (p. 324). 



2. In waters north of the Antarctic convergence (warmer than 4-0° C), however, it 

 appears that many individuals may reach stage vi by November. In Antarctic water 



