I 



HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 393 



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

 shown in Fig. 134, the data thus marshalled revealing the heavy massing of the total available 

 feeding-stuff in the northern ice-free waters of the Weddell zone and showing that in general it would 

 be the Atlantic stocks of whales that would be the earliest to encounter ample feeding during their 

 southern migration, the Indian and Pacific stocks, the former first in the West Wind region south-east 

 and south of Kerguelen, encountering it progressively later. 



Summer. The distribution and relative abundance of the staple whale food in summer (January- 

 March) is shown in Fig. 135. 



The rapid growth, particularly in the Weddell zone, of the first year swarms in December leads 

 by the end of the month to their abrupt^ and almost complete transition from the small to the staple 

 class with the result that in summer, when the modern pelagic whale fishery is in full swing, the 

 mass of the latter everywhere becomes enormously augmented. The effect of this transition is to be 

 seen in the pronounced abundance of the large to enormous concentrations of the over 20 mm. class 

 that is now to be found not only in the northerly Weddell zone, but also (although less conspicuously) 

 in the southerly high latitude region of euphausian abundance in the East Wind drift. In the southern 

 zone, however, the transition is much less abrupt than in the Weddell drift, many of the young, just 

 over one year old, swarms in these high latitudes (p. 379 and p. 397, Fig. 136) persisting until 

 March predominantly as early adolescents in the 1 1-20 mm. range, and this in part at least might 

 account for the relative scarcity of exceptionally large concentrations of the over 20 mm. class apparent 

 there. 



In the northern zone, it will be seen, there are large to enormous summer concentrations in the 

 Bransfield Strait, in Weddell West, on the South Georgia whaling grounds and in the western half of 

 Weddell Middle. Farther east, in the southern half of the current between 15° W and 20° E, there 

 are minor, large and enormous concentrations, for the most part rather widely scattered, and in the 

 northern half of the current between the same meridians there appears to be an extensive region of 

 scarcity which in view of the rich 11-20 mm. population recorded there in spring (p. 377, Fig. 123) 

 at first seems highly anomalous. It will be seen, however, that over a large part of Weddell Middle, 

 in the northern half of the current between 15° W and 0°, there are virtually no summer observations, 

 whereas the spring observations in the same area are many (Fig. 123) and cover it closely from 

 west to east. In the northern part of Weddell East our summer coverage is also rather meagre with 

 only 27 surface hauls as against 63 in spring. It will be seen, too, that in the same region there is 

 a large area between 4° and 16° E which although well sampled in spring, in one instance with an 

 enormous positive result, was not examined in summer. 



Turning now to the East Wind drift it would appear from our records that exceptionally large 

 concentrations of the staple class are not of such common occurrence in these high latitudes as they 

 are, for instance, in the western Weddell drift, on the South Georgia whaling grounds and in Brans- 

 field Strait; and it has already been suggested that this apparent scarcity may be due in part 

 at least to the fact that the augmenting of the staple class by the outgrowing of the 11-20 mm. 

 adolescents is a more protracted phenomenon in the southern than in the Weddell zone. The greater 

 frequency of occurrence of very large gatherings in the lower latitudes may be associated too with the 

 fact that our stations there were distributed more or less equally between daylight and darkness, 

 whereas in the East Wind zone the vast majority were made in the continuous summer daylight of 

 these high latitudes — conditions tending to involve our observations in some error, rather difficult to 

 measure, arising through the avoiding action which, in broad daylight in particular, thekrill, even when 

 only half-grown, can readily take of the surface nets. In this coastal region of abundance, with its 



^ Abrupt at least in the Weddell zone. 

 46 °" 



