346 



DISCOVERY REPORTS 



A * «, | A 



V V V V "V h 



Ai' -Vi 



Fig. 174. 



N 



/^ f I A ^ f 



;"a 



w 



WIND 



I 



r 



V 'V 



' I 1 



:; 



A/ 

 Fig- 175- 

 *» ■/>. '/, /, ■/, /, 



NE 



/ 

 / 



7. 



periphery of the curving current. In this 

 manner an assembly of animals might 

 be kept circulating in one area whilst the 

 water masses were continually passing 

 on. In actual practice an animal would 

 rarely be brought back to exactly the 

 same place, but with swirling current 

 systems as we see round South Georgia 

 in the meeting and mixing of the two 

 streams of Bellingshausen Sea and 

 Weddell Sea origin, varying slightly 

 in salinity and temperature, we may 

 often get conditions which might hold 

 assemblies of animals for considerable 

 periods in one neighbourhood. The 

 probable maintenance of patches of 

 Euphausia superba in one place from 

 one month to another has been demon- 

 strated by the whale concentration 

 charts shown in Figs. 155 and 156 on 

 pp. 292 and 293. 



We may now consider the move- 

 ments of vertically migrating animals 

 in relation to surface waters moved by 

 wind. In Fig. 175 let the main water 

 mass — fine broken lines — be moving in 

 a north-easterly direction. Now a west 

 wind will have the effect 1 of causing 

 the surface stratum to move at 45 ° to 

 the main water mass, i.e. to the north, 

 shown by continuous fine lines. Thus 

 an animal starting at A will be moved 

 under the influence of this westerly 

 wind, not in a more easterly direction 

 as one might first of all imagine, but in 

 a path to A'. In Fig. 176 an easterly 

 wind is shown acting upon a similar 

 water mass moving to the north-east; 

 the surface stratum is again deflected at 

 45 from the main water mass, but 

 this time to the south, and an animal 

 would move from A to A'. 



1 In the southern hemisphere. I am indebted to Mr G. E. R. Deacon for this information regarding 

 the influence of wind in moving the surface stratum in relation to the lower mass. 



G 





A"" 



I i i 





■/! 



' /. 



WIND 



5 



Fig. 176. 



