46o DISCOVERY REPORTS 



An unusual feature of this season was that towards the end, when Blue and Fin whales 

 seemed to become less plentiful a considerable number of Sei whales were taken. 



As in 1925-6 the great majority of whales of both species caught in the earlier part 

 of the season (November to January) were adult, but the average length diminished 

 considerably in the second half, through the appearance of large numbers of immature 

 whales ; these came to form a majority in the catches of Blue whales and at least a fairly 

 high proportion among the Fin whales from about February onwards. 



In contrast to the previous season the ratio of immature Blue whales for the whole 

 season was reduced to 27 per cent. The proportion of pregnant females, 43 per cent, 

 is a great increase over previous seasons. A greater proportion, 48 per cent were 

 resting, but very few (7 per cent) were lactating. The latter were all taken in the later 

 part of the season. 



There were relatively rather more immature Fin whales this season. A very high 

 proportion of the adult females were pregnant but the percentage fell heavily in April. 

 A moderate number were lactating in the later part of the season. 



The causes of the fluctuations in the catches which have been described above must 

 now be considered. In spite of the small number of seasons over which the observa- 

 tions have extended there are indications that certain features and fluctuations are more 

 or less constant, while others are variable. Taking the constant features first we see from 

 a glance at Plates XLIII and XLIV that nearly all the time the sexes are equally dis- 

 tributed throughout the season. The only exception to this appears in the sudden influx 

 of Fin whales in January 1926 when for a few weeks males were in a great majority. 

 At Saldanha Bay the sexes were equally distributed through the whole season. From 

 this it may be inferred that, in general, the sexes are evenly distributed in the whale 

 " communities " but that in some cases a certain amount of segregation may take place. 

 Again, when the first and second halves of a season at South Georgia are compared 

 it is found that in the first half the catch is composed of a majority of mature whales, 

 while in the second half there is an influx of immature whales (and perhaps 

 a withdrawal of adults) which causes a sharp reduction in the average lengths. 

 It is quite probable that observations over further seasons will show that this is a regular 

 phenomenon. It is evident in both Blue and Fin whales, though perhaps more marked 

 in the former. Reference to the tables on pp. 456 and 457 suggests that there is a 

 tendency in each season for pregnant whales to be more numerous in the first half of 

 the season and lactating whales in the second half. It should be noted that the lactating 

 whales in October and November 1926 form an exception to this. 



Apart from the fact that immature whales have occurred in relatively greater numbers 

 in the latter part of the season, there is an indication that of the adult whales themselves, 

 those taken early in the season are mostly older than those taken later. In the section 

 on the ages of whales it was shown that adult females could be divided into three age 

 groups mainly according to the numbers of corpora lutea in their ovaries. There are 

 not sufficient data to enable us to compare the separate months of each season in this 

 respect, but if the three seasons are amalgamated, the majority of adult females of both 



