320 WHALES 



mainly of diatoms, needs sunlight, it is found chiefly in the upper fifty 

 fathoms, and particularly in the top 5-10 fathoms, where there is, inter 

 alia, the greatest concentration oï Fragilariopsis antarctica (see Fig. 133), 

 krill's chief source of food. For this reason, krill, though present down to 

 500 fathoms, is most prolific in the top 5-10 fathoms, and it is here that 

 Avhales chiefly forage for it. 



Though plankton is fairly evenly distributed over the entire Southern 

 Ocean, it is particularly abundant south of the Antarctic Convergence. 

 Krill, hoAvever, forms an exception because it is rarely found as far to the 

 north as the Antarctic Convergence, ^vhere the temperature of the water 

 is apparently too high for it. In the thirties, biologists associated with the 

 Discovery Committee made many long voyages to the Antarctic and 

 collected tens of thousands of plankton, and particularly krill, samples 

 from most areas. The first results were published by F. C. Fraser (1936) in 

 his detailed paper on the distribution and development of the young stages 

 of krill, while Miss Bargmann (1945) dealt with the life history of adoles- 

 cent and adult krill. In 1956, when, after years of painstaking research, 

 J. W. S. Marr of the National Institute of Oceanography published the 

 first results and a preliminary chart (Fig. 178) of further work on the 

 distribution of krill, experts learnt to their surprise that krill is concentrated 

 in two areas: in the region of the East Wind Drift, i.e. mainly south of 

 63° S., and in the Weddell Current (Fig. 177). The Weddell Current 

 arises where the East Wind Drift, after having passed the Weddell Sea, is 

 deflected by Graham Land. Augmented by currents from the Pacific, the 

 current then carries vast masses of cold water to the north-east, passes 

 South Georgia, and continues as far as about 55^ S. Its influence can be 

 felt as far as 30° E., i.e. about as far as Cape Town. In other words, only 

 between 60° W. and 30° E. and up to 55° S. is krill found in large concentra- 

 tions, while elsewhere such concentrations are not found beyond 63° S. 

 Moreover, the chart shows clearly that individual concentrations are not 

 uniformly dense, probably as a result of local diflferences in the direction of 

 the currents and the temperature of the water. One such irregular current, 

 for instance, is found just outside the Ross Sea, where a shelf impedes the 

 return flow of the water. 



Whales may reasonably be expected to keep to regions where there are 

 large quantities of krill, and, by and large, this is borne out by the whaling 

 statistics which, inter alia, give the number of whales caught per square 

 often degrees (Fig. 179). However, the statistics must be regarded with 

 some reserve, for though the annual catch certainly depends on the number 

 of whales in a given area, such factors as weather conditions, distance from 

 the nearest harbour, or intense hunts in past years, may affect the results 

 of whaling expeditions in particular regions. Fortunately, in addition to 



