is6 DISCOVERY REPORTS 



afternoon numbers of Crocodile Fish {Parachaenichthys georgiantis) lurking near the bottom were seen 

 to be preying on the swarm. The fish would leap up and dart at the krill overhead and although many 

 were captured and eaten, others with a single kick of the telson would spring backwards 4 or 5 in. to 

 avoid the fish, often breaking surface as they did so or leaping clean out of the water altogether. 



The backward kick is accomplished with astonishing speed and it is probably with this that the 

 krill most frequently avoid approaching danger or obstacles to their forward way. I quote from 

 Ommanney (1938): 'The "krill" is a creature of delicate and feathery beauty, reddish brown and 

 glassily transparent. It swims with that curiously intent purposefulness peculiar to shrimps, all its 

 feelers alert for a touch, tremulously sensitive, its protruding black eyes set forward like lamps. It 

 moves forward slowly, deliberately, with its feathery limbs working in rhythm and, at a touch of its 

 feelers, shoots backwards with stupefying rapidity to begin its cautious forward progress once again'. 



In another note on a swarm of adult krill he watched in the open sea off South Georgia Gunther 

 mentions that the euphausians persistently avoided the ship's side, the whole swarm keeping a good 

 5 or 6 ft. away and never coming within 4 ft. of it. In the same note he states that when a lead on a 

 line was thrown into the swarm it parted suddenly to right and left leaving an avenue of clear water 

 some 5-9 in. wide, tentatively concluding that similar avoiding action might well be taken by krill of 

 this size when touched by, or confronted with a clear view of, the warp and bridles of an approaching 

 net. 



Clearly then, by the time it is half-grown, if not before, E. superha far from remaining a passive 

 drifter, has on the contrary become a creature of great agility, powers of locomotion, purposeful intent 

 and not a little awareness. It has been shown, for instance, that it can stem and without difficulty 

 make headway against a current of considerable force, can gather enough momentum to break surface 

 and leap surprisingly high out of the water, is by no means indifferent to sudden disturbances and 

 incursions in its vicinity and is prepared and able to take active measures to avoid them. Indeed, when 

 one considers its reaction to the approach of a boat for instance, or to the quick thrust of a marauding 

 fish, or when suddenly confronted with or touched by a foreign body such as a lead on a line, it is not 

 surprising that the proper interpretation of the catch-figures revealed by the random sampling of our 

 nets should present a problem (pp. 258-84) of considerable magnitude. 



The principal facts that emerge from these eye-witness accounts are (i) E. superba quite early on 

 in its development, already that is when half-grown, ceases to be strictly planktonic and begins to 

 behave, particularly in well illuminated conditions near the surface, with much of the vigour and 

 awareness of a nektonic organism, (2) the patch or swarm is a unit, complete in itself, that does not 

 break up except under the influence of sudden or violent external stimuli, a unit that even so will 

 quickly re-form, and (3) the individuals of a swarm, all it seems heading in the same direction, can 

 maintain themselves, regardless it seems of surface drift, over a given position for hours — Hardy for 

 instance mentions a ' whole day ' — on end. 



It will be recalled that Gunther's swarm 'appeared' off the jetty. It was not there in the morning. 

 In other words it must have come from seaward, it being unlikely that it came from up-harbour where 

 the water is foul, much contaminated with factory refuse and red with the blood of dismembered 

 whales. Moreover, it must have moved in against the tide which was ebbing when it first appeared. 

 All this suggests that the swarms we see on the surface, in other words swarms in early or late ado- 

 lescence, or in their adult state, do, as swarms, move bodily about, not necessarily however helplessly 

 under the influence of tidal streams or other more far-reaching water movements, but evidently under 

 their own very considerable locomotive power. As Marshall (1954) has said, ' . . .the well-muscled, 

 shrimp-like euphausiids and mysids and the smaller deep-sea prawns are almost certainly active enough 

 to keep station in the face of moderate currents. Perhaps it would be better to place these organisms 



