IMPACT OF THE WHALES ON THE SWARMS 245 



depletion is continually being replenished (p. 384) by fresh influxes of euphausians from the East 

 Wind drift as it sweeps coastwise up from the Weddell Sea.^ It cannot, it seems, be without some 

 significance that marks fired into o-group whales in this krill-rich field, with two exceptions, have 

 (where recovered) all been recovered inside it, always allowing of course (Dawbin, 1959) that the 

 distribution of the recoveries in this region was something more than simply a measure of the distribu- 

 tion of the marking and chasing vessels. 



In his recent study of the distribution and movements of blue and fin whales in the Atlantic sector 

 Arsenev (i958^>) states that during the summer the herds are always on the move in search of food, their 

 position at any time being fixed by the Euphausia they eat. He finds too that in the Weddell drift their 

 principal movement while feeding is from north-east to south-west, that is, counter to the surface stream. 



It has been assumed for some time (Chittleborough, 1958) that the stocks of humpback whales in 

 Antarctic areas iv and v are distinct and that they do not intermingle. Recently, however, from an 

 analysis of the data forwarded to the Bureau of International Whaling Statistics, Chittleborough 

 (19596) has demonstrated what seems to have been a large influx of humpbacks from area v westwards 

 into area iv in the summer of 1958-9, and recent recoveries of marks from this species (Brown, 1959) 

 suggest the movement may be of regular occurrence. Regarding what seems to have happened in 

 1958-9, Chittleborough remarks, 'it seems reasonable to suggest that an environmental change 

 (possibly of a temporary nature) resulted in some change in the distribution of euphausiids, enabling 

 the humpback whales in the Group v population to feed farther west than usual '. It is possible, 

 I suggest, that they were obliged to feed farther west than usual, easy access to the krill-rich fields 

 of the East Wind zone perhaps having been denied them owing to a northerly, and perhaps only local, 

 extension of the ice-edge, compelling them to move west, counter to the West Wind stream, in search 

 of their summer feed. Similar West Wind movements, apparently skirting the northern periphery of 

 the East Wind zone, seem to have been undertaken in the same season by blues and fins (Brown, 1959). 



In his most recent account of the feeding and movements of baleen whales Nemoto (1959) suggests 

 the interesting possibility that if rich Antarctic feeding-grounds are already occupied in ' biological 

 strength ' by the early migrating blues, the late comers, the fins, might be obliged to seek their food in 

 other waters, and this he concludes would account for the segregation of the larger southern feeding 

 whales into groups of fins and groups of blues. 



Between 1945 and 1957 a total of 960 blue, fin and humpback whales was marked in the Antarctic 

 (Clarke and Brown, 1957) and the work is still going on. It will be interesting to see if future recoveries 

 provide further evidence of the feeding movements the marking experiments so far seem to suggest. 



INTIMATE STRUCTURE OF THE SWARMS 



Sex ratio 

 Table 49 shows the proportion of males to females in samples from swarms in which the sex ratios 

 have been accurately determined. The figures are based partly on the sex determinations published 

 by Bargmann (1945, Appendix, Table 19) and partly on the field observations of other members of the 

 Discovery staff. Only samples of fifty individuals or over have been included. 



In the majority of instances, it will be seen, these almost exclusively random gatherings show 

 repeatedly that the swarms are composed of males and females in approximately equal numbers, the 

 three instances of non-random sampling, namely, where nets were deliberately towed through swarms 

 seen on the surface, also showing a sex ratio which for all practical purposes is unity. There are 

 comparatively few instances where the males vastly outnumber the females or vice versa, and it is 

 1 Especially, it seems (pp. 384 and 390), in summer, from January to March. 



