368 DISCOVERY REPORTS 



whales which did not occur among the large adults. It was felt that although the 

 number of percentage measurements on which averages were based would be lessened 

 by doing this, the large and small whales had evidently very different histories and 

 must on that account be separated from one another. 



The averages for each month of the thickness measurements (each measurement 

 having been expressed as a percentage of the whale length) are shown in Figs. 105 to 

 I ID. Small whales certainly immature have been separated from the large adult whales. 

 Thus Fin whales shorter than 18 m. and Blue whales shorter than 19 m. represent the 

 immature group, while Fin whales longer than 20-0 m. and Blue whales longer than 

 23-0 m. are considered mature. 



The average blubber thickness for all Fin whales is about 0-3 per cent of the total 

 length. This represents a whale of normal fatness. For example, a 20 m. Fin whale 

 should have blubber 6 cm. thick. The corresponding average for Blue whales is 0-35 per 

 cent, which means that a Blue whale of 20 m. is fat or lean according as to whether its 

 blubber is thicker or thinner than 7-0 cm. We will now consider each sex of the two 

 species in turn. 



Male Fin Whales (Fig. 105). In this graph the 1925-6 season is separated from that 

 of 1926-7, but the results are very similar. An evident increase in thickness takes place 

 among mature whales during the season at South Georgia. 



It will be noticed that the immature whales appeared at the island in February and 

 March, i.e. towards the end of the season, and that they were far less fat than the adults. 



At Saldanha Bay the lean immature whales contrast well with the few fat mature 

 whales of August and September. There is a hint of a decrease in blubber thickness 

 here which is more evident in the other groups. 



Male Blue Whales (Fig. 106). In the case of male Blue whales the increase in the 

 thickness of the blubber in adults from below normal in November to above normal 

 in March is seen. A rapid fattening of immature whales in the second half of the season 

 is also evident. 



At Saldanha Bay the fatness of the large whales and leanness of the small ones is 

 apparent, as it was among male Fin whales. Here again is a suggestion of a decrease 

 in thickness as the season advances. 



Female Fin and Blue Whales. Among the female whales complications arise due to 

 pregnancy and lactation. Pregnancy is known to have a profound effect on the blubber, 

 the fatness of pregnant whales being noticeable at the whaling stations as soon as the 

 blubber is cut. 



Lactating whales, characterized by leanness at South Georgia, have been found at 

 Saldanha Bay to be extraordinarily fat. To deal with these differences pregnant, lactating 

 and resting females have been separated. 



The resting females of both species (i.e. those neither pregnant nor lactating) may 

 be taken first (Figs. 107 and 108). The mature whales at South Georgia, of normal 

 fatness from November to Februar}^ show a rather sudden increase in blubber thickness 

 at the end of the season. The immature females, like the immature males, arrived for 

 the second half of the season, and on arrival were normal or rather lean. 



