234 DISCOVERY REPORTS 



of its contemporary or neighbour, a phenomenon only to be expected in view of the protracted period 

 over which the eggs are laid. The data provided by the special method used for sampling the surface 

 patches in daylight confirm these appearances. This method, which is described on p. 152, was first 

 used at Station WS 540, where in the short period of 35 min. five samplings, each producing an 

 enormous quantity of euphausians, were carried out on five separate but adjoining patches, each lying 



NON -IDENTICAL ADJACENT SWARMS 



IDENTICAL ADJACENT SWARMS 



Fig. 44. The patches as swarms. Length frequency in five separate adjacent patches sampled at St. WS 540, showing the 

 distinct variability of age pattern that can be exhibited by neighbouring swarms (Length scale in 2-mm. groups, e.g. 

 30 = 29-30 mm.). 



approximately 400 yards from its neighbour. The length frequencies of these gatherings, based in 

 each instance on the measurement of over 600 individuals, are shown in Fig. 44. It is clear from these 

 graphs that in three instances (samples B, D and E) the patches represent swarms of practically 

 identical age and that in two instances (samples C and A), they represent swarms, C older and A still 

 older, than B, D or E. In terms of spawning A would represent the earliest, C a somewhat later 

 spawning, and B, D and E a later still. It is unlikely that some chance advantage of environment or 

 feeding could be responsible for the advanced condition of A and C since all five swarms are located 

 too close to each other in space and time for that to be possible. 



If the krill were not so discretely disposed, but scattered broadcast throughout the whaling grounds, 

 the persistently recurring normal length frequencies characteristic of our samples, and the high modal 

 values that go with them, would both disappear, and the length frequencies, ceasing to have normality, 

 would exhibit random and inconsequential modes instead. 



In view of the astronomically large numbers of larvae that must be produced to maintain the older 

 population at its existing fantastic level our vertical gatherings of the young stages are on the whole 

 surprisingly small. So enormous in fact must the larval population be, that I should have expected it 

 to have been sampled with much the same success as for instance (Hardy and Gunther, 1935, 

 Appendix 11) certain copepods are, but manifestly in the main (Table 48 and Figs. 45-8) it has 

 not. A possible explanation of this anomaly is that the larval swarms, like the older swarms we see 



