i64 DISCOVERY REPORTS 



rence of gravid females should indicate whether there is a concentration of the latter in 

 the region of pack-ice. The few records of gravid females in the present material show 

 that some were taken off the coast of South Georgia (St. 356), some in the Bransfield 

 Strait (St. 548), some off the Biscoe Islands (St. 602), and some at a point about midway 

 between South Georgia and the South Orkneys (St. WS 376). Although the records 

 are admittedly small, yet such as exist are very widely scattered and give no indication 

 of concentration in any particular locality. 



The scarcity of adult E. superba as compared with adolescents along the edge of the 

 pack, demonstrated by the catches in the line of stations from Bouvet westwards to 

 South Georgia and in the South Georgia survey succeeding it in October-November 

 1930 (p. 149), shows that it is not at the ice-edge that one would expect to find them. 

 The numbers for the stations instanced are as follows: adults 869; adolescents, in- 

 cluding Furcilia 6, 195,164. The scarcity of adult E. superba at the ice-edge stations of 

 the circumpolar cruise has been noted by John. The ice-edge is predominantly and 

 almost exclusively the locus of adolescent krill and not of adult krill, at any rate at this 

 time of year just prior to that when spawning is believed to commence. 



It has been shown that this adolescent krill stays in the surface water which is moving 

 away from the Pole, so that it will be borne northwards in the Antarctic surface water 

 towards the Antarctic convergence. 



It may be noted here that the whalers speak of Blue whale krill and Fin whale krill to 

 describe respectively adolescent and adult E. superba. Ruud (1932, p. 46) says: 



There seems to be an undoubted correlation on the one hand of abundant drift ice with 



abundant Blue whales and krill of Group I [i.e. adolescents] and on the other hand of a small quantity 

 of drift ice with abundant Fin whales and krill of Group II [i.e. adults]. 



If E. superba spawns under and near the drift ice its spawning ground is the zone of the pack ice 

 and as a rule the conditions off South Georgia are not suitable for its spawning. The stock of krill 

 at South Georgia must therefore be carried thither by the current in the Antarctic surface layer. 

 When the newly hatched larvae drift out of the Weddell Sea with the ice they gradually develop and 

 grow in conformity with the curve of growth with which we are familiar. Group I may be found 

 comparatively far from the actual spawning ground but still near the ice; farther away, near the ex- 

 treme limits of the distribution of E. superba and at a distance from the ice there will be only Group II. 

 When there is little ice at South Georgia we only find Group II but with a great deal of ice there is 

 also a large proportion of Group I. The Blue whale is a more typical ice whale than the Finner, hence 

 the correlation of abundant ice, krill of Group I and Blue whales — and of a small quantity of ice, 

 krill of Group II and an abundance of Fin whales. 



Owing to the rotatory motion of the surface current in the Weddell Sea and other parts of the 

 Antarctic, the central spawning ground of the krill in the drift ice zone will always be supplied with 

 an ample stock of animals of Group II — sufficient to produce a large stock of larvae when they 

 spawn. 



In the light of the present data, it is necessary to make some modification in the 

 conception of the mechanism by which the return of the krill to the south is brought 

 about. 



The hydrological evidence of a complete rotatory surface movement in the horizontal 

 plane is very scanty. One would expect that a well-defined and constantly flowing 

 current southwards would be required to bring about the replenishment of E. superba 



