HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 405 



The developmental condition and length frequencies of the principal winter concentrations of 



the staple whale food recorded in the northern zone are shown in Fig. 140, the major features thus 



presented being as follows : 



(i) The staple whale food in winter is represented by a heterogeneous assemblage of swarms about 



half-way through their adolescence and ranging from 19 to 21 months old. 



(2) In July, judging from the length frequencies of the swarms encountered, the females are 



probably dominantly in stage 2.^ In August and September they are dominantly in stages 3 and 4 



(rarely 2). 



Fig. 140. Developmental condition of the staple whale food in winter. For vertical scale see legend to Fig. 107. 



(3) The swarms display a heterogeneous pattern of modal values throughout the season. 



(4) In July they tend to fall principally within a length range of 21-36 mm., appearing generally 

 in fact to be in an even more backward condition, in so far as modal values go, than the adolescent 

 swarms encountered in autumn. This, however, may be only an appearance, for it must be acknow- 

 ledged our July length frequencies, being based except in one instance (Station 2852) on rather scanty 

 material, are not altogether satisfactory. It may be, too, that more forward swarms such as we should 

 have expected to encounter at this time of year, swarms with higher modal values and superior female 

 development, were fortuitously missed. In August and September they tend to fall mainly within a 

 length range whose principal limits lie between 29 and 52 mm., the more backward mainly in the 

 29-40 mm., the more forward in the 37-52 mm. range. Exceptionally, however, as for instance at 

 Stations WS 264 and WS 277, very backward swarms of abnormally inferior modal length and with 

 females still only in stage 2 may be encountered in late August and early September. 



The winter distribution and relative abundance of the small and staple whale food combined is 

 shown in Fig. 141, from which it is clear that even during this season of much reduced over 20 mm. 

 abundance the mass of the total available feeding-stuff, in the ice-free zone of the Atlantic sector at 

 any rate, is quite substantial. It would clearly in that sector, although almost certainly not everywhere 

 in the circumpolar sea, be sufficient to sustain, should it still continue to feed, the scattered population 

 of whales that as Hinton (1925), Risting (1927), Harmer (1931), Bagshawe (1939) and more recently 

 Mackintosh and Brown (1956) have shown, remains on the ice-free regions of the feeding-grounds 

 throughout the Antarctic winter. It seems likely, in fact, that some of the large rorquals winter all 

 round the continent wherever there is enough open water and their food is in good supply. Bagshawe 



^ Of eleven July females examined by Bargmann (1945, Appendix, Table 19), three ranging from 26 to 30 mm. long were 

 in stage 2 and eight ranging from 29 to 43 mm. long in stage 3. 



