SUMMARY 437 



widespread patchiness has been encountered, sometimes involving areas estimated to be as much 

 as 150 square miles or more in extent. In such areas, as a rule, there are distances of from about 

 a third to a quarter of a mile between patches. Individual patches, although very variable in size, 

 are seldom if ever very large, the smaller covering a few square yards, the larger half an acre or 

 so, or sometimes perhaps a little more. They exhibit an almost infinite variety of shapes largely 

 because, judging from one or two inshore swarms which have been closely observed, they are in a 

 continual state of flux, constantly changing their form, expanding and contracting, elongating this way 

 or that, sometimes appearing as if about to divide or break up, only to re-form, the individuals reversing 

 or changing direction in unison, the whole phenomenon imparting to the swarm the appearance and 

 activity of an amoeba. In colour they vary from pale straw yellow, through ochre, mahogany brown 

 to brick or vivid blood red. They are seen from time to time right on, or very close to, the surface of 

 the sea and appear to be of very shallow draught, in general being disposed in shallow rafts no more 

 than a yard or two thick. The individuals pack tightly, their density, to the eye at least, appearing to 

 be of the order of one euphausian to the cubic inch. Both adolescent and adult swarms are composed 

 of exceedingly active animals reacting either individually or in unison with great rapidity to external 

 stimuli. Where they have been watched in shallow water close to fixed points of reference they have 

 been seen to be capable of maintaining their formation intact for long periods over a given position 

 against a current of considerable force. In general it can be said these vigorous swarming individuals 

 have ceased to be strictly planktonic. The swarm in fact appears to be a unit that, behaving it seems 

 as a single organism, does not break up except when violently disturbed as, for instance, by the passage 

 of a vessel, a unit that even so will quickly re-form (p. 148). 



18. Direct observation and the analyses of a very large series of net samples covering a wide bathy- 

 metric range reveal a massive concentration of the whale food at or not far below the surface, and that 

 while its absolute vertical range may extend from the surface down to about 1000 m., in so far as it 

 may be said to exist in concentrations dense enough to satisfy the needs of the whales, it is confined 

 very largely, especially at night, to an extremely narrow zone that does not, it seems, go deeper 

 than 5 or 10 m. below the surface. By day this crowded zone may become somewhat depleted owing 

 to the vertical migration of some of the swarms, particularly the older swarms, to deeper levels. The 

 daytime movement, however, does not seem to extend to depths greatly in excess of 40 or 50 m. It 

 seems, too, to be very erratic and to involve only part of the surface population. The analyses show, 

 too, that there is no mass seasonal descent of either younger or older stages into the warm deep water 

 flowing counter to the surface stream (p. 157 and p. 268). 



19. It has been roughly calculated that the density of the krill in the central part of the Weddell 

 drift might be as high as 30 g./m.^ or approximately 50 times the equivalent weight of whale flesh 

 in the inner Antarctic zone (1° isotherm to ice-edge). The same ratio it seems might hold good through- 

 out the East Wind- Weddell surface stream (p. 170). 



20. The dietary of E. superba is described in detail. It is clearly and almost exclusively a voracious 

 herbivore, and although at first sight the regular occurrence of certain small spineless diatoms in the 

 stomachs seems to point to some measure of selective feeding, it may be that these forms, being strongly 

 silicified, are not very easily digested, and that many other less strongly silicified species are equally 

 important as food (p. 172). 



21. The enormous abundance in some vertical net samples of diatomaceous faecal pellets suggests 

 strongly they are the excreta of the shoaling krill, their more or less uniform distribution from the 

 surface down to 1000 m, indicating they are sinking (p. 176). 



22. While much further exploration is required to confirm it, there is some evidence that spawning 

 as a major event is a relatively shallow water phenomenon associated principally with the shelf or slope 



