I 



REVIEW OF DYNAMICS OF DISTRIBUTIONAL CONTROL 435 



long voyage north will begin again, but it will end in the "happy event" awaited since the preceding 

 season. The whale-calf then conceived will see daylight for the first time in the same warm waters 

 which "cradled" his parents a year previously'. 



The fields of krill it is true seem inexhaustible, but one wonders how long the even yet not hopelessly 

 depleted stocks of their giant predators will be permitted to enjoy them and for how long they will be 

 allowed, in reasonable security, to conceive, bring forth and nurture their kind. 



One looks however with hope to the future, for as Bertram (1958) has written, 'The present 

 International Whaling Convention is a remarkable instrument which, if it continues to be applied 

 effectively and even more stringently, may be a monument to the idealistic zoologists of the mid- 

 twentieth century'. 



SUMMARY 



1 . A review of early historical records and recent literature emphasises primarily the abundance 

 and ecological importance of this species in Antarctic waters, its predominantly surface habitat and 

 the circumpolarity and unevenness of its distribution (p. 40). 



2. The scope of the observations is described and the limits imposed on them by the polar pack, 

 it being manifest that the periodic freezing and unfreezing of certain large areas of the circumpolar 

 sea and the permanent inaccessibility of others combine to aggravate the difficulty of studying its 

 distribution (p. 48). 



3. A broad practical outline is given of the principal features that help to distinguish it in plankton 

 samples, all developmental phases being covered from the egg to the adult state (p. 55). 



4. The high latitude coastal current in the East Wind zone and the low latitude oceanic current 

 from the Weddell Sea which the former feeds, together with the Bransfield Strait and South Georgia, 

 to which both East Wind and Weddell water penetrate, are the principal regions of its abundance. 

 Its circumpolarity, therefore, unlike that of many other Antarctic plankton animals, is essentially 

 asymmetrical, the circumpolar West Wind drift being barren or very sparsely populated, except where 

 fed locally from the East Wind drift or by overflow from the Weddell stream (p. 57). 



5. Its association with pack-ice throughout every phase of its surface development is seasonal. In 

 winter and spring vast stretches of the principal regions of its abundance are frozen over and it becomes 

 a creature of the ice, but in summer and autumn equally large stretches are unfrozen and it becomes 

 equally a creature of the open sea. Moreover, in certain areas, such as the waters round South 

 Georgia, and perhaps the northern fringe of the Weddell drift, which are neither involved in the 

 winter freeze-up nor affected by the drift of the pack, the krill are never associated with ice at all 

 except in so far as such areas are periodically infested by bergs or are penetrated by water in which 

 ice may have melted previously somewhere 'upstream' (p. 64). 



6. It is confined almost exclusively to water south of the Antarctic convergence, water in which 

 the surface temperature range shortens quite appreciably with increasing latitude, the winter minima 

 and summer maxima for the four principal regions of its abundance being: South Georgia —175° 

 and +3-90° C, Bransfield Strait -1-89° and +2-69° C, Weddell drift -1-89° and +2-50° C and 

 East Wind drift —1-89° and +1-45° C. As an older adolescent and adult it encounters its warmest 

 surface conditions (+i-oo° to +3-99° C) on the northerly South Georgia whaling grounds from 

 January to March and its coldest (-2-00° to +1-99° C) in the Weddell and East Wind zones, the 

 latter, however, slightly the colder, during the same period. In the East Wind drift the surface 

 population as a whole, larval, adolescent and adult, spends fully 10 months of the year in temperatures 

 which rarely if ever rise above zero C, the larvae and very early adolescents enduring these severe 

 conditions virtually throughout the year (see p. 409, note i). From June to November the vast majority 



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