SUMMARY 441 



depletion it suffers through the ravages of spring and summer. Winter is essentially a time of dual 

 abundance with both larvae and the early adolescents to which they are giving rise, the former in 

 enormous numbers, dominating the northern zone again to its maximum limits. It is a time, in the 

 northern zone at least, of continued scarcity of the staple class. In the East Wind or southern zone, 

 however, the larvae are probably the dominant winter class, with the staple whale food of secondary 

 importance and the small (i 1-20 mm.) group non-existent. Although the small whale food is dominant, 

 especially in the East Wind drift, spring alone is a time of triple abundance when the surviving larvae, 

 and both small and staple whale food are spread throughout the whole vast extent of the feeding- 

 grounds to their farthermost limits (p. 358). 



35. The circumpolar distribution of surface discoloration, supposedly attributable to krill swarms, 

 follows very closely that of the gross distribution of the total euphausian surface population as revealed 

 by the stramin nets (p. 412). 



36. The great summer larval outburst in the western Weddell drift and the subsequent spreading 

 of the larvae to the north and east in the surface stream are shown to be annual events (p. 412). 



37. The local distribution of the krill round South Georgia reveals a conspicuous massing of these 

 animals, in every phase of their surface development and at all times of the year, on the north-eastern 

 side of the island where the influence of the surface drift from the Weddell Sea is itself most con- 

 spicuous (p. 413). 



38. In view of the relatively short period it remains open to the major depredations of whales and 

 seals and the relative immunity vast stretches of it enjoy from the ravages of penguins, and for all we 

 can tell of a multitude of other animals as well, the East Wind drift may be conceived as being a 

 relatively untapped reserve of whale food and as such must contribute not a little to such other factors 

 as may be involved in the conservation of the krill population (p. 423). 



39. The distribution and relative abundance of E. superba and the smaller E. triacantha are com- 

 pared, it being suggested that among other factors as yet obscure the great depths at which the krill 

 eggs hatch, the lifelong swarming that ensues, the enormously rich pastures among which it finds itself 

 and is so admirably equipped to feed, its immunity to EUobiopsid infection, and the protection from 

 surface predators the overwhelming mass of its larvae enjoys throughout the polar winter, all contribute 

 something to the immense scale on which E. superba has populated the Antarctic seas (p. 424). 



40. The evolution of the feeding migrations of the baleen whales is considered in the light of the 

 geological and climatological history of Antarctica (p. 428). 



41. On the Atlantic or Weddell side of Antarctica the only mechanism we can clearly see 

 working to maintain the krill population within its normal geographical limits is the eastward and 

 southward dispersal of the very early larvae as they rise towards the surface through the warm deep 

 layer, deep larval dispersal from the lower latitudes in which the Weddell stream is flowing resulting 

 in this region in a recruitment of the high latitude west-going population in the East Wind drift 

 moving clockwise round the Weddell Sea. There is no evidence, however, that the East Wind popula- 

 tion elsewhere can similarly be replenished from so far north, the vast extent of the West Wind drift 

 east about from 30° E carrying it appears neither an adult female population nor a deep south-borne 

 population of larvae from which such replenishment could spring. Since at the same time there 

 appears to be no deep return of breeders or potential breeders from low to high latitudes anywhere 

 throughout the circumpolar sea the factors responsible for the continued existence of the west-moving 

 population throughout the greater part of the East Wind drift remain for the present obscure. There is, 

 however, in the East Wind zone itself a southward movement of the ascending larvae carried in 

 the warm deep layer, a movement operating continually to the advantage of the coastal population 

 in these high latitudes (p. 429). 



