THE OLDER STAGES 159 



grounds and in the Bransfield Strait in 1926-7 (Discovery Reports, Station List, 1929) provide 

 abundant evidence that between these critical levels (Table 29) a sharp decline in relative density 

 takes place immediately below the surface, a decline that becomes rapidly more accentuated 

 with depth. From the horizontal data in fact it would appear that the krill do not exist in any 

 substantial measure of abundance beyond an exceedingly narrow zone that probably does not go 

 deeper than 5 or 10 m. below the surface, such deeper concentrations of them as are encountered 

 being evidently only of minor importance and extending down to only 50 m. or so, or perhaps a 

 little below. 



Table 29. Vertical distribution of the staple whale food based on the gatherings of the three-level 

 horizontal nets worked round South Georgia and in Bransfield Strait 



Table 30. Orders of abundance of surface and subsurface catches recorded in and below the 



East Wind-Weddell surface stream 



Subsurface catches night 

 Surface catches night and day 



Although our townets do reveal the existence of small to moderate concentrations at various 

 levels below 5 m., principally, however, at subsurface levels above 50 m., the occasions when they 

 have done so are far from common. It will be seen (Table 30) that of the grand total of 796 closing 

 net hauls made below the East Wind-Weddell surface stream only 76, or 10%, produced catches of 

 over 10 individuals, only 31, or 4%, catches of over 100, the vast majority, no less than 90%, pro- 

 ducing negative results or catches of i-io. The corresponding figures for the surface (0-5 m.) layer 

 are, catches of over 10, 54%, of over 100, 35 %, and of i-io or negative, 45 %. Together, the 76 sub- 

 surface hauls with over 10 individuals accounted for 21,191 krill, only 392 short of the total euphausian 

 catch of 21,583 obtained below 5 m. From this it follows that 720 subsurface net hauls, 90% of the 

 total, captured between them only about half a euphausian per net, substantial evidence of how com- 

 paratively rare, or if not rare at least widely scattered, subsurface concentrations of the krill must 

 actually be. Moreover such few minor to moderately large subsurface gatherings as we have recorded 

 (Table 31) are by no means exclusively daytime phenomena, there being little significant difference 

 in the frequency of their occurrence whether it be light or dark. It will be seen too that both average 

 catch and frequency of subsurface occurrence is conspicuously high at levels above 50 m., although 

 even in this critical layer, close though it be to the zone of manifestly high surface night concentra- 

 tion, our subsurface nets have not very successfully or very often it seems, been recording the really 

 substantial concentrations that could reasonably be expected there. 



