DISTRIBUTION IN OUTLINE 63 



recorded as rich in these euphausians and such others as, equally often, have been recorded as poor.i 

 From this presentation of the data it will be seen that while the species is circumpolar as has always 

 been supposed, and as Baker (1954) has now definitely shown, the northern limit of its occurrence 

 however falling increasingly away to the south as one travels from the Atlantic side of Antarctica 

 eastwards round the continent, in the major aspects of its distribution (Fig. 5 b) it exhibits a circum- 

 polarity of marked asymmetry. For instead of being evenly distributed all round Antarctica approxi- 

 mately between the same latitudes throughout as certain other circumpolar plankton animals (John, 

 1936; Baker, 1954; David, 1955) are known to be, it manifestly has on the one hand a high latitude, 

 and on the other a low latitude distribution closely associated with the surface movements of the 

 colder Antarctic waters. In fact it is clearly never found in any real measure of abundance except in 

 (and, as will be shown later, under) two great surface streams — the west-flowing East Wind drift 

 moving coastwise in high latitudes all round Antarctica and the great outflow of cold water to which 

 this coastal stream gives rise as, moving westwards into the Weddell Sea, it strikes the projecting mass 

 of Graham Land lying athwart its path and, as the Weddell current, or, as some prefer to call it, the 

 Weddell drift, is deflected northwards and eastwards into relatively low latitudes. In brief it is enough 

 for the present to observe (i) that the main concentrations of the krill, whatever the stage of its 

 development, are confined almost exclusively to these two great currents and to the South Georgia 

 and Bransfield Strait whahng grounds to which they penetrate, and (2) that the rest of the circum- 

 polar sea, or West Wind drift as it has been called, the whole vast expanse of it eastwards of 30° E 

 where the Weddell stream appears to lose its impetus, has little to offer as a feeding ground for the 

 questing whales.^ Indeed but for the existence in it of certain strictly limited areas afl^ected by tongues 

 of cold water deflected from the East Wind region by submarine ridges, the West Wind zone as far 

 as the distributional problem is concerned could virtually be disregarded. A notable instance of such 

 deflection is the movement associated with the Kerguelen-Gaussberg Ridge, the northerly encroach- 

 ment of cold water to which it gives rise carrying with it minor concentrations of euphausians, almost 

 exclusively, our data show, furcilias or early post-larval forms, far to thenorthof their normal latitudes. 

 In so far as this particular deflection is concerned it may be remarked that along the Antarctic coast 

 south of Australia the East Wind stream flows strongly, the Australian expedition of 191 1-14 (Davis, 

 1919) reporting it turning sharply to the north-west in 97° E where the projecting mass of Termination 

 Ice Tongue 3 lay athwart the westerly flow. Other instances of East Wind encroachment into the 

 West Wind zone will be noted, for example north of the Balleny Islands, north-east of the Ross Sea, 

 west of Graham Land and in the Drake Passage. 



As an indicator species, above all as an indicator of the major movements of the great Antarctic 

 surface streams, E. superba in fact may be regarded as supreme. 



The overriding importance of the East Wind- Weddell surface stream as a carrier of the krill, and 

 the relative unimportance of the West Wind drift, is demonstrated again in Fig. 5 c which shows all 

 gatherings of 100 or more of the older stages of the whale food* (euphausians over 20 mm. long) which 

 (p. 147) provide the major portion of the diet of the whales. This figure illustrates too how in the depth 

 of winter, with the ice-edge (Herdman, 1953) lying far to the north of its summer mean, searchers 

 would fail to strike the krill in any substantial measure of abundance throughout a vast area of the 



1 How poor in fact such regions are will be shown repeatedly in the main section on the horizontal distribution which 

 begins on p. 284. 



* How little will again repeatedly be shown in the main distributional part. See also the monthly West Wind catch-figures 

 given in the Appendix. 



' Termination Ice Tongue (Cumpston, 1939) has now broken away. 



* All, that is, but for around South Georgia where our observations (Fig. 2) are too crowded to permit every such 

 gathering to be shown on the circumpolar chart. 



