PHYSICAL ENVIRONMENT 67 



numbers in the open sea. In spring too this group, consisting of FurciHa 6 and early adolescents, and 

 the later adolescents of the 16-20 mm. class are exceedingly abundant at the ice-edge, but again there 

 is no evidence of this being the exclusive habitat of these stages, judging from the vast numbers of both 

 groups, particularly of the latter in November, we find in ice-free water. As for the older stages, the 

 scarcity of adults at the ice-edge upon which John and Fraser remark is seen to be confined exclusively 

 to the winter months, June, July and August, when there is a corresponding, although less pro- 

 nounced, scarcity of these stages in the open sea. The winter scarcity of older animals, however, both 

 at the ice-edge and elsewhere, is perhaps hardly surprising when one considers the magnitude of the 

 depredation that must be wrought by the multitudes of whales and other creatures that devour them 

 during the spring, summer and autumn months. We have every reason too to believe (p. 399, Fig. 137 

 and p. 404, Fig. 139) that the dying-off of the adults that have paired and spawned contributes further 

 to the winter decline. 



A comparison of the average catches at the ice-edge and in open water over the whole year shows 

 that in both regions of abundance there is little significant difference in the average catch-figures for 

 the three size groups wherever they are encountered in Antarctic waters. In order to obtain strictly 

 comparable annual catch-figures the averages shown at the bottom of Table i are based exclusively 

 on the months during which the three size groups, both at the ice-edge and in open water, severally 

 have their optimum range and, as Table i shows, are at their maximum abundance. Thus, taking 

 first the average annual catches at the ice-edge, the months principally affecting the under 16 mm. 

 group are June to November, the 16-20 mm. group September to November and the over 20 mm. 

 group September to May. The corresponding months for catches in the ice-free zone are March to 

 November for the under 16 mm. group, and for the 16-20 mm. and over 20 mm. groups as for the 

 ice-edge. 



Taking now a regional view of the matter it will be seen from Table i that the enormous numbers 

 of larvae and adolescents we find at the ice-edge at certain times of the year is a phenomenon strictly 

 characteristic of the East Wind-Weddell surface stream, and not of the vast extent of the circumpolar 

 ice-edge wherever elsewhere it may be encountered. The ice-edge eastwards of 30° E, which, as 

 Mackintosh and Herdman (1940) show, reaches far northward into the West Wind drift from May 

 to December, is clearly, certain special parts of it excepted (see below), not involved, for whereas 

 the average annual ice-edge catches of the under 16 mm. and 16-20 mm. groups in the East Wind- 

 Weddell stream are 3145 and 1201 respectively, the corresponding figures for the ice-edge of the West 

 Wind drift are a mere 18 and 21. The abundance of larvae and early adolescents at the ice-edge 

 reported by John (1936) was recorded at one station in the East Wind drift, where 2046 larvae were 

 encountered, and at thirteen stations located in two of the several cold tongues of this coastwise 

 current that (p. 58, Fig. 4) get deflected into the West Wind zone (the 'special parts' referred to 

 above) under the influence of submarine ridges. Even in these special parts, however, judged by East 

 Wind-Weddell standards, John's ice-edge abundance was not a very marked one, the average catch- 

 figure for the thirteen net hauls upon which it rested being only 123. 



The situation in the East Wind zone proper, disregarding that is the several tongues of it that 

 encroach upon the West Wind drift, does apparently reveal (Table 2) a decided preponderance of 

 larvae at the ice-edge in April and May. The preponderance, however, is unreal simply because in 

 these high latitudes, as the distributional charts show (p. 322, Fig. 84; p. 348, Fig. 102), the main 

 mass of the larvae is confined to a relatively narrow coastal belt which at this time of year is already 

 almost completely frozen over so that in effect there is virtually no open East Wind water any 

 longer accessible, such as there is being well outside the principal region of larval abundance 

 there. 



5-a 



