384 DISCOVERY REPORTS 



to cease rather abruptly east of 30° E, and how such overflow as takes place beyond this meridian is an 

 overflow primarily of adolescent forms chiefly affecting the region between 30° and 60° E. Thus 

 Fig. 128 shows how the young surface swarms, at first purely as larvae, gradually spread along 

 the Weddell drift from west to east between December and April, Fig. 129 this movement in 

 greater detail and Figs. 130 and 131 how as larvae and early adolescents, the former from May 

 to November, the latter from July to December, they remain heavily massed throughout the entire 

 Weddell surface stream without undergoing any major onward movement to the east except as 

 adolescents in spring. The spring manifestation of the easterly influence of the Weddell drift, which 

 is most conspicuous between 30° and 60° E,^ may be a phenomenon associated with a massive release 

 of cold water resulting from the breaking up and melting of the enormous ice-sheet it carries through- 

 out winter and early spring. 



The spring break-up, and subsequent melting and dispersal of the Weddell pack from the South 

 Sandwich Islands eastwards takes place with great rapidity. I quote from Hansen (1934): 'Before 

 melting, the zone of pack-ice usually breaks up in several places, with the result that it divides into 

 large drifting islands of pack-ice. The process of melting may take place very rapidly, especially in 

 the eastern [Weddell East] part of the zone. The factory ships may be entirely surrounded by ice one 

 day, to find themselves in ice-free water the next. Strong north and east winds, in particular, help to 

 melt the ice quickly, as the high seas they bring smash up the ice '. 



The staple whale food 



Spring. The natural starting-point for the portrayal of the distribution of this, the staple diet of the 

 whales, is spring, for it is then, notably in November (p. 370, Fig. 118), that the young, now 

 10-12 month old, swarms derived from the previous summer's spawning first begin to develop a 

 substantial over 20 mm. component. It is in spring, too, that the whales first begin to arrive in, 

 quantity on the feeding-grounds. The distribution and relative abundance of the staple feeding-stuff I 

 during this season is shown in Fig. 132. 



Taking first the position in the ice-free zone, it will be seen from a comparison of Figs. 117, 123 

 and 132 that the spring distributional patterns, whether of larval, early adolescent or staple whale 

 food, are in all material aspects the same, the principal concentrations of the staple class, like those of 

 the larvae and early adolescents, being massed conspicuously throughout the Weddell drift and very 

 conspicuously round South Georgia. In the West Wind zone there is again evidence between 30° and 

 60° E of small-scale November overflow from the Weddell stream and again of the effect of East Wind 

 influence south-east of Kerguelen, the very small to minor occurrences plotted in these two localities I 

 representing the over 20 mm. components of the mixed larval and adolescent swarms (p. 370, Fig. 118) 

 already recorded there. The West Wind drift elsewhere is barren of the staple class except again where I 

 it is affected by the current from the Ross Sea, and, west of Graham Land, by the influence of the I 

 northward flow from the East Wind drift that originates somewhere near Peter I Island. 



Turning again to the Weddell drift it will be seen that in Weddell West the spring scarcity of the j 



late larval and 11-20 mm. classes, already referred to on pp. 368 and 376, is paralleled by a similar 



scarcity of the staple class. While again this might simply be due to chance, it has been recorded it | 



seems on too many occasions, namely, in the springs of eight successive years from 1927 to 19341 



inclusive and again in the spring of 1936, for it to be ascribed to chance alone. The region manifestly is 1 



one that is subject to periodic invasion by the first and second year swarms that are carried (i) in 



the East Wind generated current flowing into it from the Weddell Sea, and (2) in the current, partly 1 



^ The major concentrations of small, mainly adolescent, whale food plotted farther east, that is, south and south-east of J 

 Kerguelen, appearing to be mainly, if not all, of East Wind origin. 



