DISTRIBUTION OF YOUNG STAGES OF EUPHAUSIA SUPERBA 165 



necessary to ensure a continuance of the abundance in which it is found in Antarctic 

 waters. Deacon (1936, p. 19) says: 



The movement towards the west, the northward current along the east coast of Graham Land, and 

 the current flowing out of the Weddell Sea towards the east, form three parts of a cyclonic movement 

 which extends across the entire width of the Atlantic Ocean. The surface temperature distribution 

 suggests that the cyclonic movement may be completed by a southward movement between 20 " and 

 30° E ; there is, however, very little evidence of such a current at the surface, although its existence 

 in the warm deep layer cannot be doubted. 



Ruud's scheme does not take into account the predominance of eggs and Meta- 

 nauplius in the region of the warm deep water, which has a component of direction 

 southwards, not northwards, neither do his data give information about diurnal 

 migration in the Calyptopis and early Furcilia stages. Two items of negative evidence 

 should also be considered — the great scarcity of adult krill at the ice-edge at the begin- 

 ning of the summer season and the lack of eggs in the proximity of field-ice in number 

 in any way approaching that obtained, for instance, at St. 540. The fact that krill does 

 not occur far inwards from the peripheral region of field-ice is also important. 



The present results suggest that replenishment of the stock of krill is assured by a 

 rotary movement involving the northward flowing surface water, the southward- 

 flowing deep water and the distribution and migrations of krill within these currents. 



The accumulation of adolescents at the ice-edge can then be accounted for by sug- 

 gesting that the resultant direction of movement in the eggs and in Metanauplius to 

 early Furcilia stages has a southerly component. The periphery of the ice-field is the 

 southern limit for the larvae, where they will tend to be massed together. This shoaling 

 is probably assisted also by the increase in area of the ice-field with the advent of winter 

 conditions and the freezing of the sea, leading to a further accumulation at the ice-edge 

 of larvae which were formerly in ice-free water. 



The habitat of the late Furcilia and early adolescents is at the surface and pre- 

 dominantly at the ice-edge. They will spread northwards in the northerly flowing sur- 

 face water, with the breaking up and drifting away of the field-ice in the spring and 

 summer. The adults, as Ruud points out, will be found at a distance from the ice. From 

 the records of the deep occurrence of eggs and early larval stages it is considered more 

 probable that they, rather than the adults returned to the south by the rotary motion 

 of the surface currents, are responsible for the replenishment of the stock of adolescents 

 at the ice-edge. 



The absence of adult krill in any abundance at the ice-edge, at a time just prior to that 

 when spawning is supposed to commence, negatives the assumption that they are 

 brought back to the drift-ice zone by rotary motion of the surface currents. At any 

 rate, if it is admitted that adolescents are predominantly at the surface and if this posi- 

 tion is maintained until the adult state is reached, it means that for about a year they 

 are in water which has a resultant component of direction northwards. In such a period 

 of time they would be carried far away from the ice-edge towards the Antarctic con- 

 vergence. 



