THE OLDER STAGES 'SS 



In an unpublished report on the field-work of R.R.S. 'Discovery 11', the late Dr Stanley Kemp 

 records that while the ship was making her way through the pack not far from Bouvet Island m 

 October 1930 great quantities of krill were almost always to be seen and he goes on to say, 'The young 

 stranded themselves in numbers on floes that we momentarily submerged in our passage, while the 

 adults with greater activity often jumped clear of the water and landed kicking on ice some 10 or 

 12 inches above the surface'. 



Jumping clear of the water, presumably when disturbed, may be of commoner occurrence in this 

 species than is generally supposed. It has not been recorded very often, probably because it is a thmg 

 that would tend to escape notice except under the conditions of absolute calm that are to be found in 

 the polar pack. I saw a remarkable exhibition of it while ' Discovery II ' was steaming south through 

 the Ross Sea pack-ice in January 1936. I quote from a note I made at the time: 



On the evening of January 7 as we were steaming across a large pool on the northern edge of the pack we saw an 

 unusual sight. In most directions there appeared every now and then a sort of fluttering in the water as if fine 

 shot had been sprinkled on it. As we looked more closely we could see that the disturbance was caused by krill 

 breaking surface rapidly or jumping clean out of the water. The phenomenon seemed to be taking place at scattered 

 points over a wide area— probably all over the surface of the pool which was several square miles in extent. The 

 evening was one of exceptional beauty with brilliant sunshine, the air being quite still and the surface of the sea dead 

 flat and glassy. We do not know if such behaviour has been observed before but we rather think it would pass 

 unnoticed except under such perfect conditions as we had that night. We did not ascertain what was causing the krill 

 to behave in this fashion but thought they may have been disturbed by the harrying of fishi as there were no penguins 

 about, or perhaps that they were simply enjoying themselves! 



In regard to the last suggestion it is interesting to record that Olsen (p. 132) also refers to daytime 

 congregations of krill on the surface 'gambolling about'. Gray (i960) has spoken in similar terms of 

 the jumping of salmon in open water, noting that while it has been regarded from time to time 'as an 

 attempt to rid itself from external parasites. May it not also be an indication of a general feeling of 

 joie de vivre or even a process of limbering up before the big race ? ' Dr T. J. Hart (personal communica- 

 tion) has seen the phenomenon of the jumping krill on several occasions. He describes it as like rain 

 falling on the water and says it can sometimes be heard. 



Possibly the most revealing of all eye-witness accounts of the habits and behaviour of this euphausian 

 is contained in some rough notes made by Gunther while watching a swarm of krill near the Govern- 

 ment Jetty at Grytviken in February 1931. I am indebted to these notes for the following paragraph. 



Round about noon a swarm of half-grown krill appeared off the north side of the jetty swimming at 

 the surface. The day was calm with the sun shining brightly out of a clear sky, and at the time of the 

 observations the tide was ebbing at a rate of about a third of a knot (about 30 ft. per min.) southwards 

 under the jetty. In spite of the current the swarm as a whole showed no tendency to drift towards or 

 under the jetty, but, heading upstream for several hours, maintained its position where first seen in the 

 full glare of the sun. Indeed the krill seemed to have a definite preference for the sunlight, for there 

 were none directly under the jetty or in the shadow it cast upon the water. One or two that did chance 

 to get into the shadow quickly swam out again, and making headway without difficulty against the 

 current^ regained their original position in the sun. On the south side of the jetty there were a few 

 isolated individuals stemming the current head on. Some swam as far as, but no farther than, the 

 shadow, and it seemed as though that constituted a barrier the krill deliberately avoided. Later in the 



1 See next paragraph but one below. Predatory fish are known to cause such behaviour among other swarming euphausians, 

 Bigelow (1926), for instance, referring to an occasion in the Gulf of Maine when dense shoals of Thysanoessa raschii were seen 

 just below the surface, the shrimps ' breaking water' to avoid the pollock that were after them. It will be recalled, too (p. 132 

 note 3), that Nemoto (1959) has seen the supposedly bathypelagic Notokpis coatsi chasing the krill on the surface. 



2 The italics are mine. 



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