PHYSICAL ENVIRONMENT 65 



the edge of the ice or even the larger lanes between the pack-ice. Evidently, therefore, there must be 

 great quantities of krill out at sea among the icebergs and drifting floes, and not chiefly near land and 

 coastal banks as suggested by Mackintosh and Wheeler. ... All whalers in the Antarctic ', he remarks 

 later, ' know by experience that the whales are often to be met with near icebergs and packs, and that 

 the krill is most abundant there'. Rustad (1934) has much the same to say, observing that the 

 ' tendency of the whales to prefer the vicinity of the ice ', is obviously caused by a similar tendency in 

 E. superba, while Bennett (193 1), referring to the diatoms with which the floes are so often stained, 

 states that 'this fact is probably the clue to the abundance of whale food near ice'. Fraser (1936) 

 concludes that the ice-edge is ' predominantly and almost exclusively the locus of adolescent krill and 

 not of adult krill ', at any rate at the time of year (October) just prior to when spawning is believed to 

 commence, adding later that the habitat of the late Furcilia stages too is also predominantly at the 

 ice-edge. John (1936) also remarks on the abundance of larvae and adolescents and scarcity of adults 

 at the ice-edge, Feltmann and Vervoort (1949) stating that the surface population as a whole is most 

 abundant in the 'immediate neighbourhood of the drift ice'. Ommanney (1949) suggests too that it 

 is along the edge of the pack that the richest fields of the krill occur. 



From the mass of data bearing on this controversial matter that has now been accumulated, it can 

 be shown that while the foregoing statements are perhaps largely true of the particular areas or times 

 of year to which they refer, they cannot be applied universally to the krill throughout its whole 

 circumpolar range or throughout its whole developmental history. In presenting these data, using 

 the material from our oblique (loo-o m.) and horizontally towed surface stramin nets, I have divided 

 the surface population into three broadly differentiated developmental phases: (i) krill under 16 mm. 

 long (vast majority larval), (2) krill 16-20 mm. long (very young adolescents), and (3) krill over 20 mm. 

 long (older adolescents and adults). Since, however, the older stages of this large euphausian are so 

 active (Mackintosh, 1934; Marr, 1955, 1956), avoiding the surface net, in some measure at least, even 

 in darkness (p. 265) and by day (p. 259) with relatively enormous success,^ the daylight surface gather- 

 ings of (3), the most successful escapers, have been omitted from the data presented. 



The relative abundance of these three developmental phases at the ice-edge and in the open sea 

 is shown in Table i . In this, and in Table 2 which follows, stations counted as ' at the ice-edge ' 

 include some in close proximity to it, within about half a mile or less, and some actually inside the 

 ice-belt itself, stations ' in the open sea ' including some with the ice-edge possibly not very far away 

 but not in sight. The vast majority however of those counted as in open water lie at distances ranging 

 from ten up to several hundred miles away from the nearest ice. 



Looking at the figures broadly (Table i) we find little to suggest that the ice-edge is predominantly 

 and almost exclusively the locus of late larval and adolescent krill as Fraser concluded, or to support 

 the view, so widely held by the whalers and others, that the whale food as a whole is most abundant 

 near the pack. Indeed, during the autumn months, especially in March and April, ^ we find conditions 

 directly at variance with Fraser's findings. For then enormous numbers of the under 16 mm. class, 

 principally Calyptopes, but including both early and late Furcilias, are present in the open sea, 

 whereas at the ice-edge the numbers are conspicuously smaller, virtually no larvae whatsoever having 

 been recorded there in March. In winter, it is true, the under 16 mm. group, now represented mainly 

 by the late Furcilias with, in June, the last surviving Calyptopes, undoubtedly occurs in enormous 

 numbers at the ice-edge, but it certainly does not predominate there, there being equally enormous 



* In so far as night evasion alone is concerned Moore (1950) goes as far as to say that with certain far smaller but highly 

 luminescent euphausians the night-time surface density has occasionally appeared to the eye to be as much as 75 times greater 

 than the corresponding density revealed by nets. 



- Our data for May are scarce and have been combined with the April data. 



