390 DISCOVERY REPORTS 



at least East Wind generated, that enters it via the Bransfield Strait. It seems possible, therefore, 

 that the relatively barren spring condition we have repeatedly recorded here, a condition in which all 

 three classes of the whale food are equally involved, is due partly to the onward passage of the young 

 previous summer's swarms to the east (p. 376) and partly to the fact that the first and second year 

 swarms upstream do not arrive in quantity in this sector until later in the year. The situation in 

 Weddell West in summer (p. 394, Fig. 135) suggests that they may not in fact normally do so 

 until January. The major and nearby minor occurrences of the over 20 mm. class plotted at the eastern 

 end of the Bransfield Strait (p. 370, Fig. 118, Stations 537 and 539) and the single substantial 

 occurrence recorded in about 37° W (Fig. 118, Station 1039) may, therefore, it seems, represent 

 isolated instances of the spring invasion of Weddell West by young first year East Wind swarms each 

 with a strong over 20 mm. component. 



Although the early adolescents are dominant (p. 376), spring is essentially a time of triple abundance'^ 

 when the surviving larvae and both 1 1-20 mm. and over 20 mm. classes are spread more or less 

 uniformly over every reach of the Weddell drift and in large, sometimes enormous, numbers are 

 present in every part of the northern ice-free zone of euphausian abundance to its farthermost limits. 

 Yet what again of the seemingly impoverished spring condition we have recorded in Weddell West? 

 Can this after all be real, or is it in fact, as I have suggested, merely an appearance that could spring 

 so readily from the chance failure of our nets to strike the surface swarms? It is true no doubt 

 that the swarms encountered there earlier in the year, especially (p. 346, Figs. 100 and loi) the 

 larval swarms, have long since passed on to the east. Yet it is difficult to see how there could ever 

 be interruption in recruitment from the East Wind drift, as it sweeps up from the Weddell Sea, 

 unless it be that periodically this coastwise stream ceases to function, or in other words comes 

 virtually to a standstill. Sverdrup (p. 432) distinctly suggests that some such interruption could happen. 



In the East Wind zone the position is more obscure. In two instances, however, where there has 

 been major penetration of the ice-belt there, namely, in the Ross Sea by the floating factory ' C. A. 

 Larsen' carrying a Discovery Investigations observer in 1928, and between meridians 45° and 75° E 

 by Mawson's (B.A.N.Z.) expedition in 1929, we have evidence that at least a moderate spring- 

 time over 20 mm. population exists. Having regard, however, to the situation there in summer, 

 throughout which, as we have seen (p. 378, Fig. 124 and p. 383, Fig. 127), substantial numbers 

 of small (11-20 mm.) adolescents still survive, and having regard, too, to the adverse effect 

 of the prolonged winter ice-cover (p. 355, Fig. 107) upon the larval growth-rate in these high 

 latitudes, there can I think be little doubt that spring in the East Wind zone is essentially a time when, 

 the surviving over 11 mm. Sixth Furcilias still contributing heavily (p. 365, Fig. 114), the small 

 whale food vastly predominates over the staple class (but see PI. III). 



The developmental condition of the principal concentrations of the staple whale food in spring, 

 based (Fig. 132) on our observations in the Weddell drift, the South Georgia area, the Bransfield 

 Strait, the West Wind drift between 30° and 60° E and the East Wind outflow south-east of Kerguelen, 

 is shown in Fig. 133. In this, as in the figures illustrating the corresponding condition in the 

 summer, autumn and winter swarms which follow, the length frequency throughout is expressed in 

 4-mm. groups, a device rendered necessary because the second year swarms, now representing the 

 main bulk of the staple class, in most instances fall within a length range too wide for the frequency 

 to be expressed adequately by the narrower, 2-mm., grouping adopted for the younger swarms. 

 As Fig. 133 shows, the length range of the second year swarms is often twice or thrice as long as 

 that of the first year swarms, and while the length frequency of the latter can be expressed quite 

 adequately by the narrower grouping (p. 370, Fig. 118) it was found that when that was applied 

 ^ See again the corresponding charts for the massed larvae and small whale food (pp. 369 and 377). 



