372 DISCOVERY REPORTS 



In these figures the actual thickness of the blubber is shown. The large whales of 

 South Georgia are a mixture of thin and fat individuals occurring during the season, 

 while at South Africa the large whales are all fat. 



The outstanding feature of the catches at Saldanha Bay is the high proportion of 

 immature whales taken, and it is to be noted that they had a very low average thickness 

 of blubber all through the season. 



The west coast of Africa seems to be a sort of nursery area for young whales and 

 it does not seem unreasonable to connect them in some way with the thin immature 

 whales which arrive in southern waters usually late in the season. 



Pregnancy and Lactation. The blubber is always thick during pregnancy. A glance 

 at Figs. 109 and no will show that the average thickness is always above the normal. 

 They appear to follow the general rule that the whales of South Georgia become fatter 

 towards the end of the season. 



Many more measurements of blubber thickness are needed for both pregnant and 

 lactating whales, but the few records available for the latter are very interesting. The 

 thinness of the blubber of these whales at South Georgia, and its thickness at South 

 Africa have already been mentioned. In Fig. no the results are shown for Blue 

 whales. There is a decrease in thickness from June to October (South Africa). At 

 South Georgia lactating whales were lean and those taken in February, March and 

 April were apparently rapidly becoming leaner. Of the Fin whales there were no records 

 for lactating females at Saldanha Bay. Those captured at South Georgia from December 

 to March were, like the Blue whales, very lean. 



There seems to be no doubt of the significance of the great difference in the measure- 

 ments at the two places. The blubber is very thick at Saldanha Bay because the whales 

 have not long given birth. From the fact that the blubber during pregnancy is at all 

 times above the normal thickness one would expect that at the onset of lactation the 

 whales would be fat. This explanation covers also the fact of the leanness of the whales 

 at South Georgia which are thus very near the end of the lactation period. 



Diatom film. Little can be said with regard to the correlation of the diatom films 

 with fatness in whales. Small patches of film occur on some whales at South Georgia 

 throughout the season. From February onwards thick films covering a large part of 

 the body were sometimes recorded. The immature whales were usually free but 

 patches were found occasionally in the later months. Two immature Blue whales in 

 March and April 1927 had thick and extensive films. 



Small spots of diatoms were seen on a few immature whales at Saldanha Bay in 

 August and September, but all the mature whales at this station appeared to be free. 

 Conditions favouring the rapid growth of diatoms occur in southern waters in February, 

 March and April, and as has been shown, at this time the whales are rapidly becoming 

 fatter. 



