338 DISCOVERY REPORTS 



South hidian Ocean and Amtralian Sector. Winter months, April, May, 

 June 1932 (Fig. 25, Table VI e) 



Fig. 25 shows the population analysed into stages in the South Indian Ocean in April, 

 at three stations in the Australian Sector in May and one in June. 



The population in April in the Indian Ocean Sector is younger than one would expect 

 if spawning had taken place in December, as it apparently did in the Falkland Sector. 

 Stages iii, iv and v are the dominant stages in diflferent proportions. At St. 851 par- 

 ticularly large numbers of stage iii were taken in the surface haul. In the absence of 

 further data we must conclude that spawning took place later in this sector of the 

 Antarctic in the season 193 1-2 than it did in the Falkland Sector. 



On the line from Enderby Land to Fremantle, where the catches were in the lower 

 nets, the stock consisted mainly of stage v, with a high proportion of stage iv (35-40 per 

 cent). At the most northerly station (862) there was a high proportion of stage iii. In the 

 absence of more complete data it is not possible to do more than note that the population 

 in the warmer waters of the Antarctic Zone at this time of year seems to have been 

 younger than the population in the colder water. The explanation of this might perhaps 

 lie in the different vertical distribution of the various copepodite stages in different 

 places. It is seen that adults were quite absent from the line from Enderby Land to 

 Fremantle, although present in large proportions, especially in the lower nets, on that 

 from Cape Town to Enderby Land. They have presumably sunk below the 250-m. 

 level on the line to Fremantle. Thus also it may be that more stage v copepodites have 

 sunk below the 250-m. level at St. 862 than at St. 860 and more again at St. 860 than 

 at the two more southerly stations. 



At St. 887, at the pack-ice edge south of Australia at the end of May, we find that a 

 spawning had evidently recently taken place. Great numbers of stages i and ii, with 

 nauplii, were taken in the surface net. This is the only station in the Australian Sector 

 at which any Rhincalanus were taken in the surface net, and the catch was a com- 

 paratively large one (533), while the number in the lower haul was insignificant (54). 

 At St. 891, just south of the convergence on the way to Melbourne, we find the genera- 

 tion which must have resulted from this spawning in stage iii, and in the lower nets only. 

 This, then, is the mid-winter spawning of the previous season's summer generation, and 

 the population sampled at Sts. 887 and 891 consisted of the young over-wintering genera- 

 tion which, as we may conclude from what has gone before, will pass the winter mainly 

 in stages iv and v below 250 m., and reappear at the surface in the spring. There is no 

 evidence from the data available as to the limits within which the winter spawning took 

 place, but it seems probable that it occurred throughout the entire range of the Antarctic 

 waters, since young stages were found at St. 891, near the convergence, as well as at 

 St. 887 at the edge of the pack-ice. The stock in the warmer Antarctic waters (St. 891) 

 appears to have spawned earlier than that at St. 887, at the pack-ice edge, having reached 

 stage iii by the end of May while that at St. 887 was only in stage ii. This, however, is 

 what we might expect from our observations in the Falkland Sector during the 

 summer. 



