THE BLUBBER OF WHALES 365 



Other differences in the thickness of the blubber are recognized by the flensers at 

 the whahng stations in South Georgia. Thus whales covered with the brownish-yellow 

 film of diatoms are fatter than those without it, and the large Blue whales taken at the 

 end of the season are fatter than those taken earlier. 



During our three seasons' work at South Georgia and one at South Africa a large 

 number of blubber measurements were obtained. It is not suggested that the work 

 done in these areas is complete, for many more measurements must be collected before 

 more than good general indications of the changes in the blubber can be shown. 

 Further, it is unfortunate that the data in any year must be broken by a period of 

 several months owing to the closing of the stations. Our measurements, however, are 

 sufficient for tracing the effect of differences in the length of the whale, changes taking 

 place during the year, the effect of pregnancy and lactation, and so on. 



As explained on p. 267, the thickness of the blubber was generally measured at a 

 point opposite the dorsal fin and on the flank midway between the mid-dorsal and 

 mid-ventral lines. 



Changes in blubber thickness with length of whale. The Blue and Fin whales taken 

 at the whaling stations have a fairly definite range of size. Nearly all Blue whales 

 measure from 17 m. to 26 m. and nearly all Fin whales from 15 m. to 23 m. By comparing 

 the averages of blubber thickness for metre length differences between these limits it 

 is possible to find whether the thickness of the blubber is correlated with the size of 

 the whale. The results for each species and sex are shown graphically in Figs. loi to 

 104. It is seen from these that in addition to differences in the volume of blubber 

 present, due to the different sizes (i.e. areas) of the whales, there is a relative general 

 increase in thickness with increasing whale length. The average difference in actual 

 thickness of the blubber of the smallest and largest w'hales is about 2"5 cm. 



The large whales captured off Saldanha Bay are relatively fat. The graphs show that 

 they were actually fatter than whales of corresponding length at South Georgia, while 

 South African whales at the average length at which sexual maturity is reached were 

 leaner than those of South Georgia. The explanation of the differences in the average 

 thickness will be apparent later when the thickness of the blubber in relation to the 

 size of the whale is considered and the nature of the stock of whales off the South 

 African coast is examined. 



By calculation of the thickness of the blubber as a percentage of the total length of 

 the whale, comparison is possible between the thickness of the blubber of all whales 

 of the same species and sex apart from the changes due to differences in length. 

 This method shows whether any seasonal increase or decrease in thickness occurs and 

 — in the females — how much the blubber is affected by pregnancy and lactation. 



Before considering the results it should be pointed out that at the station in Saldanha 

 Bay the catch was almost entirely composed of immature animals giving a decided 

 impression of leanness which contrasted strongly with the extra fatness of the few 

 large whales captured there. This fact suggested that a separation of the measurements 

 in both areas into two groups might show changes in the blubber of the immature 



