^o DISCOVERY REPORTS 



that many of the earUest larval 'risings', as I have called them (p. 204), take place well inside the ice- 

 belt, especially (Fig. 4 and p. loi. Table 17) in Weddell West, where no research ship in fact, at the 

 right time of year, has yet penetrated, and in these cases the krill, very early in its developmental 

 history, would clearly be dependent on the pack, or if not dependent, at any rate associated with it. 

 In the more easterly parts of the Weddell drift (p. 311, Fig. 75 and p. 325, Fig. 86) we find as 

 I have said an abundance of young surface forms long after the ice there has gone. In Weddell East 

 for instance (Fig. 4), as late as mid-April, we strike an enormous concentration of Calyptopes 

 (Station 2316) which clearly must have sprung (p. 313) from a rising that originally took place in 

 open water farther west long after the last of the ice had vanished from this region. Still later, in May 

 and June (p. 317, Fig. 79 and p. 328, Fig. 88), we find Weddell East, still largely ice-free, teeming 

 with Calyptopes and early Furcilias, and these again could hardly have been carried along with ice 

 that must have melted away some four or five months earlier. Finally, there is evidence from the 

 well-sampled waters round South Georgia which are never^ invaded by pack-ice at any time of year. 

 In these island waters it appears (p. 190) there is little if any successful spawning, the annual recruit- 

 ment of the population being largely maintained it seems by surface-borne incursions of larvae, 

 principally, our data (p. 327) show, furcilias, having their origin in the Weddell Sea. Such larvae 

 must spring from Calyptopis risings a long way to the south or south-west, some of them no doubt 

 in the ice itself, but since the first large scale incursions, at their earliest, do not appear to take place 

 until April (p. 422) it seems clear enough, from the mean position of the summer ice-edge (p. 293, 

 Fig. 65), that the time elapsed between the earUest major appearances of the Weddell larvae at the 

 surface in January (p. 310, Fig. 74) and their advent at South Georgia must be spent by the young 

 drifting forms largely in a packless sea. It is clear too, from the virtually year-long ice-free condition 

 of these island waters, that once the larvae get there and subsequently grow to the adult state, they 

 must go through this lengthy developmental phase entirely independently of the pack. 



So far we have been considering only the fringe of the circumpolar pack and its relation to the 

 distribution of this species. Let us turn now to another matter, also of controversial opinion, the 

 question of the abundance or otherwise of the krill deep inside the Antarctic ice-fields. 



The sea ice of Antarctica may broadly be divided into (i) non-permanent ice which, as Mackintosh 

 and Herdman's ice-charts show, at certain times of the year, notably in winter and spring, but not at 

 others, spreads over large areas of the Weddell and West Wind drifts and over the whole extent of the 

 East Wind drift, and (2) permanent, or at any rate more or less permanent ice-fields of variable extent 

 such as are found in the Weddell Sea west of the 30th meridian, in the Pacific sector south of 

 70° S, and along the northern fringe of the Ross Sea between 65° and 75° S. It is doubtful, of course, 

 if any of the sea ice round Antarctica, with the possible exception of the high latitude ice-fields on 

 the Pacific side and in the heart of the Weddell Sea (see again p. 49), could properly be described 

 as permanent. The term, suitably qualified, is used here as a convenient contrast to (i), the non- 

 permanent ice, which is known to clear away from the areas it covers more or less regularly year after 

 year. The so-called permanent ice-fields I have in mind, however, are known to be very compact and 

 to be composed of floes of great extent and thickness, and, relative to that of the non-permanent ice, 

 their existence is prolonged and their dispersal highly irregular and unpredictable. 



Let us consider first the non-permanent ice. Here it must be admitted we have no direct observa- 

 tions, the risk of freezing-in in winter when it is so widespread rendering it imprudent to venture 

 a vessel more than a mile or so inside it. Even so there can be little doubt that the whale food, whether 

 larval, adolescent or adult, in or under the non-permanent ice of the circumpolar West Wind drift, 



1 Never it is true, in the sense that South Georgia is completely enveloped by the pack. The ice-edge (p. 417, Fig. 148) 

 is in fact occasionally found not very far away from the south-eastern tip of the island in winter and especially in sprmg. 



