24 8 DISCOVERY REPORTS 



the southern continents than to the east. Larger numbers have certainly been caught on 

 the west coasts, and the explanation is probably to be found in the hydrological condi- 

 tions. Currents tend to flow southwards off the east coasts and northwards off the west 

 coasts, so that in a given latitude the temperature is higher on the east than on the west 

 side. Upwelling of cold water rich in nutrient salts gives rise to a more abundant fauna 

 off the west coasts (especially that of South America), and it may be that whales thus 

 have a better chance of finding some food than off the east coasts. 



It is worth mentioning that the opinion has sometimes been expressed that the 

 Humpbacks migrate northwards up the west coast of Australia, cross the Indian Ocean, 

 and return through East African waters to the Antarctic. It is difficult to know on what 

 grounds such a theory could be based. It receives no support from the evidence of whale 

 marking, and on both sides of the Indian Ocean the whales have been described as 

 moving northwards at first and returning southwards later. The suggestion is in any case 

 refuted by the statistics of foetal length and yield of oil. If the Humpbacks took such a 

 circular route the foetuses of those taken off Madagascar should have grown to a greater 

 length than those of whales taken off Western Australia, but in the International 

 Statistics (1938, no. XI, p. 35) the average length of the Australian foetuses is given as 

 13 ft. 11 in. and those of Madagascar as 13 ft. 3 in. Similarly, whales should become 

 thinner through scarcity of food during their traverse of the Indian Ocean and those off 

 Madagascar should yield less oil than those arriving off Western Australia from the 

 feeding grounds of the Antarctic. But in the same issue of the Statistics (p. 32) the oil 

 production per Blue whale equivalent is given as 101-5 barrels off Western Australia and 

 105-8 off Madagascar. 



Matthews (1937) points out that there is a higher proportion of immature Humpbacks 

 in catches off Natal and Saldanha Bay than at South Georgia. The International 

 Statistics (1937, no. x, p. 21 and 1938, no. XI, pp. 24-31) give the following average 

 lengths (in feet): 



This indicates that the average length of the whales found in summer in the Antarctic 

 is slightly greater than that of those found in any of the winter coastal resorts, but it 

 would seem that the highest proportion of immatures occurs in temperate waters (Cape 

 Province and Natal) rather than in the tropics, if a lower average length may be taken 

 as a criterion. Presumably there is a tendency among immature whales sometimes to 

 stay in warmer waters rather than to migrate to the Antarctic. 



