HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 395 



virtually nightless^ summer, the migrating of the older swarms away from the surface by day must 

 lessen still more the chances of making enormous surface gatherings there. 



In the Atlantic sector of the East Wind zone attention may be focused on the large area between 

 20° W and 30° E in which all developmental phases of the surface population, larval, adolescent and 

 adult alike, are absent or conspicuously few.^ The locality has been visited and this scarcity recorded 

 on twelve separate occasions, observations, in aggregate covering every month of the summer, having 

 been made in 1930, 1931, 1932, 1933, 1935 (twice), 1936, 1937 (twice), 1939 (twice) and in the autumn 

 of 1938 in April, the last month in which it remains open to vessels. This repeatedly recorded 

 scarcity, it will be seen, occurs in a region that apparently separates a broad east-flowing zone of 

 abundance in the north from a relatively narrow, coastal, west-flowing zone of abundance in the 

 south, and the region it is suggested might be a backwater, not in fact an actively moving part of the East 

 Wind-Weddell surface stream to which the principal concentrations of the krill are virtually confined. 



Turning now to the New Zealand side it will be seen that there is another large area, the great 

 expanse of shelf water at the head of the Ross Sea, which to all appearances is barren, again of all 

 three classes of the whale food alike. This phenomenon has already been discussed at some length on 

 pp. 123-6 where, to recall the matter in brief, it was shown that the absence of E. superba from these 

 high latitudes can partly be explained by the fact that the larvae, being carried for part of their 

 existence in the warm south-flowing deep current, cannot, except as occasional stragglers, penetrate 

 on to the shelf because it acts as a barrier to this southward movement. It will be recalled too that in place 

 of the true southern whale food there, there are found vast quantities of another swarming euphausian, 

 E. crystallorophias, which, superficially resembling the krill both in size and behaviour, doubtless is 

 the food of the minke whales so abundant near the Ross Barrier, and, as Mackintosh (1942) 

 also suggests, of the blue and fin whales which, as Villiers (1925) records, that great exploring whaler, 

 C. A. Larsen, with such immense effort,^ hunted in these exceptionally high latitudes in 1923-4. 



Throughout the West Wind drift the scarcity of the staple class is pronounced, most conspicuously 

 in the heavily sampled Pacific region except, near 90° W, where it is affected by the north-going East 

 Wind flow near Peter I Island. It can be seen, however, that there is now more evidence of the 

 presence of krill in the Pacific sector where the East Wind zone was accessible to sampling here and 

 there. In the West Wind region south-east of Kerguelen only negligible numbers seem to be present, 

 a scarcity of the older krill which appears anomalous in view of the moderate to substantial occur- 

 rences of both early and older adolescents (p. 392, Fig. 134) recorded there in spring. The summer 

 scarcity in this locality, however, could well it seems be put down to inadequate sampling. The minor 

 Pacific concentration recorded in the West Wind region in about 135° W (p. 397, Fig. 136, Station 2244) 

 is probably not a true West Wind occurrence. It was recorded in a position where the wind was from 

 the east, and since the winds reported both north and south of it were also from that direction, it could 

 well it seems have been located in the East Wind drift the northern boundary of which, although 

 plotted a little to the south, must vary considerably. 



The northern limit of abundance of the staple summer feed then, is manifestly the northern 

 boundary of the East Wind-Weddell surface stream, while its absolute northern limit, it is interesting 

 to note, is not the Antarctic convergence, as has hitherto been supposed, but practically everywhere, 

 except in the neighbourhood of South Georgia, far to the south of it. The situation at South Georgia 

 is to be expected in view of the strong tongue of Weddell water that flows past the island, some- 



^ Virtually nightless in the sense that the hours of darkness are so few. 



^ See the summer charts for the massed larvae and very young adolescents (Figs, no and 124). 

 ^ The rigours of whaling in the extreme cold of these far southern grounds and the almost insuperable difficulties that 

 Larsen had to contend with are described by Dakin (1934). 



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