DISTRIBUTION OF YOUNG STAGES OF EUPHAUSIA SUPERBA 143 



we obtained a quantity of krill. They were adolescents of an unexpectedly small size, the majority 

 being a little smaller than those taken along the Weddell Sea ice-edge three months before." 



The observations made during the circumpolar cruise are of great help towards a 

 better understanding of the development and distribution of E. superba. The dominance 

 of successive stages is made clear; in April Calyptopis 3 and early Furcilia stages are 

 most abundant, in May Calyptopis stages have disappeared and Furcilia 2 predominates, 

 in June it is Furcilia 6 and in September adolescent forms which have the chief place. 



The concentration of the larvae at the ice-edge with the coming of winter is demon- 

 strated. In April it is found that larvae occur both at the ice-edge and at a distance from 

 it (Sts. 852-855), but in May, June and September they are concentrated exclusively at 

 the ice-edge. It has been suggested above that at Sts. 861 and 862 the presence of larvae 

 away from the ice-edge is connected with the deflection northwards of Antarctic surface 

 water along the west side of the Kerguelen-Gaussberg ridge. In support of the sugges- 

 tion that the larvae have been carried northwards in the surface water is the occurrence 

 of typical ice-frequenting plankton at Sts. 861 and 862, and the absence of such 

 plankton and young krill at five preceding stations, all of which, like Sts. 861 and 862, 

 were made in the hours of darkness. 



Movement southwards of the krill is ultimately limited by the ice-edge (see p. 159), 

 and accumulation of larvae in that region is brought about by this limitation and 

 augmented by the expansion of the area of ice-covered water with the coming of winter. 

 At stations made in May, June and September no krill was found except at the ice- 

 edge : its absence elsewhere can be explained if advance in time of year is brought into 

 account. The southward movement of larvae developed in more northerly regions will 

 have been terminated by the ice-edge being reached, and accumulation there will have 

 been speeded up by the northward spreading of the ice field with the advent of winter 

 conditions. In the Falkland sector it was found that in the summer larval krill was 

 diffuse in its distribution, and there is no apparent reason against assuming a similar 

 distribution in other parts of the Antarctic. On the other hand, the observations made 

 during the circumpolar cruise give clear evidence of concentration in the vicinity of 

 the ice-edge in winter. It is likely that the changes of distribution are brought about 

 by the factors mentioned above. 



Material caught in the i-m. nets 



For information about the occurrence of larvae in their second season the data sup- 

 plied by the oblique hauls of the i-m. nets will be considered. The material is de- 

 rived from stations made by R.R.S. 'William Scoresby' during the seasons 1928-9, 

 1929-30 and 1930-1 ; and by R.R.S. ' Discovery II ' during the season 1930-1. The time 

 of year covered is from August to February, but the number of observations for the 

 latter month and January is very small. 



It will be found convenient to take the stations in their chronological order, starting 

 with the William Scoresby stations in August 1928. 



