PATCHINESS 257 



On p. 210 we have described a dense patch of young E. superba only a few feet across 

 observed in one of the fjords. The habit that this Enphausia has of occurring in these 

 dense swarms helps one to understand how it is that the great rorquals — the Blue and 

 Fin whales — are able to take in sufficient nourishment from the plankton to maintain 

 their huge bodies. The patchiness of this organism has again been frequently demon- 

 strated by the fact that at the same station the N ioo H net near the surface or at some 

 lower depth may have caught very few, whereas the N 70 H net following it at the same 

 depth may have caught a great many and vice versa. 



E.frigida was only taken in considerable numbers in series St. WS 53, and here only 

 one not very dense patch was recorded (Fig. 131). Whilst specimens were taken over a 

 continuous length of 2 miles the concentration was only over half a mile of this length. 

 It suggests that this species too is essentially patchy in its distribution. 



Salpa fusiformis var. aspera also shows marked patchiness, but here the size of the 

 patches would seem to be much larger. Series 1 50 shows one very dense patch of three 

 miles across, and three other patches of much smaller numbers also of two or three 

 miles across; series WS 53 stopped perhaps in the middle of a large patch. The irregular 

 distribution of this form is shown in Fig. 135 together with that of the Amphipod 

 Vibilia. We have already discussed on p. 199 a suspected ecological link between these 

 two forms, and it is significant that in each case the patches of Vibilia correspond with 

 those of Salpa in position and approximately in proportionate numbers. This is perhaps 

 the strongest piece of evidence in support of this association. 



In each of the charts illustrating the consecutive net series a scale of time is also 

 given. The fact that the patches of Euphausia superba end at 0100 o'clock must not 

 be taken to mean that there were definitely no more such patches beyond this point — 

 there may have been patches below the line of tow of the nets which were not lower than 

 5 m. depth. The series of patches may indicate the upper limit of vertical migration 

 like the crest of a wave coming into the line of observation between 1830 and 0100 

 o'clock, but being below it before and sinking below it again after these times. This 

 conception is illustrated in the diagram in Fig. 136. In each series, Sts. 150 and WS 53, 

 we see the big patch of Salps occurring at approximately 0300 o'clock and smaller patches 

 earlier. In Fig. 123, showing the vertical migration of Salps, we saw that they tended to 

 come up towards the surface late in the night, so that the small patches sampled on the 



caught nearly twice as much as each of the nets G, T and V . Thus if we count net O as two patches the cal- 

 culated width of a patch becomes approximately 170 yards. This of course is only a possibility, since we 

 must only occasionally cut across the diameter of a patch — more often than not we cut an arc across it — and 

 net O may represent the only patch we have cut at the diameter; and again we must not assume that all the 

 patches are the same size. The small samples between two large samples may well represent arcs cut through 

 large patches lying to right or left of the track of the ship. All we are attempting to do here is to indicate 

 that whilst the patches may be very much smaller as far as our evidence goes it is likely that they are not 

 larger than some 200 yards across. Again they may not be circular patches at all but possibly long bands 

 of plankton cut transversely by the path of the ship ; a possible mode of formation of such bands is discussed 

 in Part V on p. 353. If they are indeed bands it is likely that they would have a width not greater than that 

 estimated for the diameter of the supposed circular patches. 



