I 



SUMMARY 439 



24. Neither animal exclusion nor pack-ice appears to have anything to do with patchiness which 

 seems to spring from the lifelong habit of this species of congregating in discrete swarms in which the 

 individuals are all of the same, or much of the same, age. This phenomenon can be traced from the 

 earliest deep appearance of the Nauplii, throughout the developmental ascent, the whole subsequent 

 life-cycle of the larva in the surface, through early and late adolescence and up to the adult state. 

 With the advance of summer and autumn in the northern zone the age pattern exhibited by the surface 

 swarms becomes increasingly complex as successive batches of eggs hatch out and the existing swarms 

 become augmented by others of later generation. In the southern or East Wind zone, however, 

 largely because of the much compressed spawning season there, the corresponding age pattern is 

 distinctly homogeneous. The rafting or shallow draught of the swarms (17) seems to be a phenomenon 

 persisting from hatching onwards (p. 215). 



25. The gaps or 'voids' separating the swarms, so long as they remain untenanted, must be 

 enormously richer in phytoplankton than the water occupied by the congregating krill which in their 

 packed myriads must constitute a grazing unit of immense local destructive power (p. 240). 



26. The whales, once they reach the feeding-grounds, probably come upon their food partly by 

 chance, partly by sight and partly, it is suggested, through the sensitivity of the wax plug in the external 

 auditory meatus to high-frequency vibrations produced perhaps by the swarming krill (p. 241). 



27. Many of the smaller swarms are probably swallowed by the whales outright, although clearly 

 the larger swarms would not be demolished so quickly. Single whales, or small groups of them, would 

 tend to remain longer in an area of good feeding than large schools, which, by virtue of their greater 

 capacity for local destruction, would shortly have so grossly depleted the swarms on which they preyed 

 that they would be compelled to move on in search of less impoverished fields. The results of whale- 

 marking suggest that the feeding whales do not by any means move entirely at random, but in the 

 main tend to travel against the surface drift in the East Wind-Weddell stream that is carrying their 

 food as it flows (p. 243). 



28. The swarms in general are composed of males and females in approximately equal numbers. 

 In adult swarms, however, it is not uncommon to find the gravid females vastly predominating over 

 the males, suggesting that the latter after pairing are the first to die off. Almost throughout the life 

 of the swarm the male is the dominant partner, being slightly larger and always more sexually advanced 

 than the female. After pairing, however, the female appears to undergo a short period of accelerated 

 grovi^th, becoming in the end, both in size and numbers, the dominant partner in the swarm (p. 245). 



29. The growth of the swarms in the northern and southern zones is compared, it being apparent 

 that in both stature, in so far as length frequency may be said to express stature, and development, 

 the East Wind swarms, following the late and much curtailed spawning that occurs in these high 

 latitudes and the subsequent slow larval growth-rate there, tend persistently to lag behind their 

 northern contemporaries virtually throughout their existence in the plankton (p. 251). 



30. The occurrence of cast skins in the plankton coincides (i) with the period when both yearling 

 and two year old krill are growing at their maximum intensity, and (2) it seems with the spawning 

 season (p. 256). 



3 1 . The reaction of the krill to ship and nets in varying conditions of light intensity and turbulence 

 of the sea is examined in detail, it being apparent that the samples obtained by conventional stern nets 

 provide little indication of the natural density of these animals in the sea (i) because the ship in its 

 passage may scatter their surface concentrations, and (2) because of the comparative ease with which 

 the krill, both as individuals and swarms are able to dodge the nets. Our samples, however, 

 manifestly provide a basis for an estimate of the relative density or abundance of this species in 

 one region or another and equally for estimates of the limits of its optimum abundance and absolute 



