400 DISCOVERY REPORTS 



Thus Weddell West has been sampled nearly five times more thoroughly in summer than in autumn, 

 Weddell Middle nearly seven times and Weddell East two-and-a-half times, the overall summer 

 coverage of the whole current system being more than quadruple the autumn coverage. Disparity in 

 coverage, therefore, especially such pronounced disparity as these figures reveal, might well be held 

 to account for the apparent autumnal decline, although to what extent it might in fact account for it is 

 difficult to gauge. The most that can be said is that it must account for it to some extent since with 

 a discretely swarming organism such as this the probability of striking it in mass in any given area 

 must at least decline as the observations decline. In the final appraisal of our results, therefore, it 

 must be acknowledged that there can hardly fail to be some, perhaps small, measure of unreality in 

 the autumnal scarcity we record. 



It cannot, however, be altogether unreal, for although our autumn coverage by summer standards 

 is small, it is by no means insignificant. In fact in the western and eastern parts of Weddell East and 

 on the South Georgia whaling grounds it is fairly substantial, or at any rate substantial enough to have 

 provided at least some indication of a pronounced autumnal abundance if any such existed. It must, 

 moreover, be significant that meagre by summer standards although our autumn coverage generally 

 may be it is manifestly adequate to reveal the enormous concentrations of larvae (Fig. 112) that 

 throughout this season are to be found spread along the Weddell stream from west to east. It must 

 be equally significant that our vertical observations in autumn (p. 347, Fig. loi and p. 348, Fig. 102), 

 although fewer and still more widely scattered (especially in May and June) than those of the stramin 

 nets, also reveal the great autumnal abundance of larvae in this surface stream without any suggestion 

 of doubt. 



In her study on the development and life history of adolescent and adult krill Bargmann (1945) 

 finds that after breeding the adults appear to die oflF, disappearing from the plankton by May. She 

 notes, however, that since spent females actively feeding at the surface are found in April, the absence 

 of third year adults from the very scanty material available to her in autumn and winter might perhaps 

 only be an appearance and not the result of 'a holocaust consequent on exhaustion after breeding'. 

 It seems, however, from the pronounced autumnal scarcity revealed in Fig. 137 that such a holocaust 

 might after all be a reality and that although some of the paired and spent (25-27 month old) swarms 

 may survive for a short time into April (p. 401, Fig. 138, Station 207) the majority do it seems die off" 

 with the result that by May the whaling grounds, formerly teeming with adolescent and adult swarms,^ 

 are probably left largely depleted of the latter and carrying it would appear (Fig. 138) the rising 

 adolescent generation alone. ^ Such a major loss of total available feeding-stuff might well, it seems, 

 in some measure at least, account for the autumnal decline. If, however, it should be that the adults 

 of both sexes having paired and spawned, do not in fact die off and that their virtual absence from our 

 autumnal gatherings is simply due to chance or inadequate sampling, then we should have to suppose 

 that this species, having reached full adult stature, is by autumn already about to embark on yet 

 another, a third, whole year of life. The developmental condition of the oldest swarms we meet in 

 winter, however (p. 405, Fig. 140), shows this to be distinctly improbable. There is evidence it is true 

 (p. 255 and p. 402) that some swarms might in fact live to be fully three years old or more, but it 

 is slender, suggesting that such as do survive for so long are very rare. 



Finally, I would emphasise, this season of apparent depletion, when the volume of the staple feed 

 is evidently at a very low ebb, falls at the end of a long period, covering, in the northern zone at least, 

 some six months or more, during which a horde of predators, whales, seals, penguins and a multitude 



1 That is, staple whale food in the second and third year of their growth. 



* I am speaking here in terms of total available feeding-stuff. The whaling grounds, in addition to this rising generation, 

 are now of course carrying an enormous larval population, as yet too young, however, to be available as food for the whales. 



