SOUTHERN BLUE AND FIN WHALES: SUMMARY 469 



The condition of the reproductive organs together with the gradation in the sizes of 

 foetuses, and the mean curve of growth which can be derived therefrom, confirm the 

 hypothesis that pairing takes place for the most part during certain months in the southern 

 winter, reaching a pronounced maximum in June and July, and that gestation lasts for 

 a little less than a year. It is further shown that not less than two years elapse between 

 successive pregnancies in a whale, but that two years is probably the normal interval. 



An examination of the sizes of young whales at different times of year strongly 

 suggests that the nursing period lasts for six or seven months, during which the growth 

 of the calf is very rapid, and that sexual maturity is reached about two years after birth. 

 This rapidity of growth is corroborated by evidence from other sources. 



A discussion on the ages of whales follows the question of the rate of growth. For 

 whales less than two years old, the age can be determined from the total length by means 

 of the curves of growth for young whales. After the attainment of sexual maturity a 

 clue to the ages of females is to be found in the accumulations of old corpora lutea 

 in the ovaries, and though calculations on this basis are somewhat speculative, it appears 

 that a remarkably small proportion of the females included in the catches are more than 

 about six years old. 



The study of the relations of breeding, nourishment, distribution, etc. consists 

 partly in an investigation of the food and thickness of the whale's blubber and partly 

 in a more general consideration of the stock of whales. At South Georgia the food, 

 which consists entirely of Eiiphausia superba, is very plentiful, but off the African coast 

 food is very scarce. The thickness of the blubber reflects fairly well the condition of 

 nourishment of a whale except where it is affected by pregnancy and lactation. 



An analysis of the different species and "classes" of whales included in the catches 

 reveals (o) a marked distinction between the local whale populations of South Georgia 

 and South West Africa, and (b) a tendency for the population at South Georgia to 

 undergo important changes both in the course of the season and from year to year. 

 Some of these changes appear to recur annually, while others are variable and are 

 probably to be attributed to changes in the environment and ultimately perhaps to 

 meteorological conditions. 



In the last section of the memoir the practical aspects of the results are considered, 

 and attention is drawn mainly to the following points : 



1 . The general similarity of all the whales examined suggests that it is possible for a 

 reduced number of whales in one locality to be replenished from the population of another. 



2. The ratio of immature whales killed is unduly high, especially at South African 

 stations. 



3. The protracted breeding season, the freedom from molestation by man during 

 this period, and the rapid growth to maturity all favour the maintenance of the stock. 

 On the other hand, the very slow rate of propagation is to be set off against these points. 



The economic extravagance of whaling in South African waters is specially emphasized, 

 and it is pointed out that although the industry here is on a small scale, a maximum 

 of damage is inflicted on the stock relative to the profit obtained. 



