HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 287 



of the surface larvae en masse, beginning with the period January to March, or summer,^ when the 

 young swarms first begin to be taken in quantity in the stramin nets, and ending with the same period 

 15 months later when the last few Sixth Furcilias surviving in the East Wind zone finally disappear 

 from the plankton. Next come the charts showing the distribution of the young adolescents, the very 

 small whale food between 1 1 and 20 mm. long, a group for which the most convenient starting-off 

 point is winter (July, August, September) since it is then, notably in July, and again it must be 

 emphasised probably in the Weddell drift alone, ^ that the Sixth Furcilias that spring from the earliest 

 hatching, or hatchings, first begin to moult and become adolescent. From winter then the young 

 adolescent distribution is traced through spring and summer until autumn (April, May, June) a year 

 later, when the small whale food seems practically everywhere to have outgrown itself and is no longer 

 to be found on the feeding-grounds. 



The charts showing the seasonal distribution and relative abundance of the staple (over 20 mm.) 

 whale food complete this series, beginning with spring (October, November, December), when the 

 whales begin to arrive in quantity on the feeding-grounds, and ending with winter (July, August, 

 September) a year later, when the whaling season is long past and the whales themselves have com- 

 pleted their northward migration. These final charts, being of greater concern to the industry than 

 the others, were to have been accompanied by the repetition, on a reduced scale, on the pages 

 opposite those on which they severally appear, of the corresponding charts for the massed larvae 

 and young adolescents, thus providing at a glance an overall view of how the larval, small and staple 

 sizes, in other words the total euphausian surface population, are severally distributed and rival one 

 another in dominance from season to season throughout the year. Unfortunately this plan was too 

 late for publication and the reader is referred back to the originals instead. 



As in the presentation of the vertical data composite end-charts showing as before, but here 

 by seasonal symbols, the gross distribution of the size groups they follow, severally complete the 

 three sets of charts based on the gatherings from the stramin nets. 



This series, like the vertical series, ends with a single chart based on the analysis of every sample 

 examined from the surface waters since these investigations first began. It shows the gross or absolute 

 horizontal distribution and relative abundance all the year round of the total euphausian surface 

 population, presenting the catches of the stramin nets in their entirety, the gatherings of larvae, 

 adolescents and adults at each station being combined into one, frequently enormous, whole. 



The order of presentation of the distributional charts, with the pages on which they appear, is as 

 tabulated on p. 288. 



The distributional charts throughout are provided with monthly, or where necessary, seasonal, 

 circumpolar coverage diagrams showing the number of vertical or towing stations made every 30° of 

 meridian south of 50° S. This, it will be seen, is a critical parallel, virtually enclosing the whole 

 horizontal range of the krill. It is, however, an arbitrary limit, sometimes well outside the northern 



^ The seasons into which I have split up the year are not the true astronomical seasons of the southern hemisphere. The 

 true astronomical southern summer, for example, is December, January and February, not January, February and March. 

 Yet the latter three, although collectively not the true southern summer, may for all practical purposes be regarded as such 

 in these high latitudes. More appropriately perhaps, they might be said to represent the true geographical summer since 

 it is then that the pack-ice is at its farthest south and an all round coverage of the circumpolar sea is permitted to vessels, and 

 to whales, up to the highest latitudes. Since, moreover, the whole of the modern pelagic whaling season now takes place during 

 January, February and March the grouping of these three would seem from every point of view to be a more natural and 

 practical one than that of December, January and February. 



2 Not necessarily, however, in the higher latitudes of the East Wind drift. Judging from the persistence there of a sub- 

 stantial very young adolescent population (p. 397, Fig. 136) until well into March, a population that clearly must have 

 been derived from a spawning that took place a year or more before, it seems highly probable that even if the Sixth Furcilia 

 does exist in these high latitudes in July, it does not moult on a major scale until some considerable time afterwards. 



