462 DISCOVERY REPORTS 



the Blue whales in these two seasons was correlated with the position of the ice. The 

 suggestion is that a big herd of Blue whales had travelled further south than South 

 Georgia early in the 1925-6 season, a few stragglers being caught in the first month or 

 two, and that a herd of the same kind visited the island in the 1926-7 season. On this 

 occasion they perhaps found the conditions they sought further north than before and 

 thus remained in the vicinity instead of travelling further south. 



It has already been shown that the average age of the adult Blue females in the 1926-7 

 season was distinctly greater than in the 1925-6 season. 



A rather more definite view can now be taken of the nature of the whale population 

 which is exploited at South Georgia. It may be suggested as a working hypothesis that 

 it is composed partly of sections of the main stock of whales and partly of whales 

 whose movements are influenced less by the movements of the main stock than 

 by some other factor. One would imagine that the movements of the main "herds" 

 (recognized by their large numbers, high average age, high proportion of pregnant 

 whales, etc.) would be controlled mainly by the distribution of food, and the meteoro- 

 logical conditions, and as these conditions vary from season to season the appearance 

 of these big herds at South Georgia is also liable to vary. 



On the other hand, we have the whales which appear at South Georgia independently 

 of the main stock. Among these the lactating whales are probably to be counted, for it 

 seems probable, apart from a certain regularity in their appearance near the end of the 

 season, that they lead a comparatively secluded life while nursing the calf, which 

 presumably would not be strong enough to keep up with the majority of adults during 

 the southern migration. The immature whales are perhaps the most prominent among 

 those which appear independently of the main stock. An explanation of their appearance 

 at South Georgia later than the majority of adults might be that being smaller they also 

 take longer over the southern migration. Finally, there are what seem to be schools of 

 stragglers which include many resting and rather few pregnant whales and which may 

 yet form a considerable proportion of the whole stock of whales. These are mostly rather 

 young whales. 



This view of the make-up of the whale population round South Georgia is of course 

 to be taken as a hypothesis which must depend for its substantiation on the results of 

 some more seasons' work at South Georgia and the analysis of statistics from past 

 seasons. However, it is probably not far from the truth and it at least gives an adequate 

 explanation of the catches in the three seasons during which the work has been carried 

 on. Risting's analysis of the catches cannot be used much for comparing previous 

 seasons in this connection as he does not indicate the fluctuations in sizes, percentage 

 pregnant etc. from month to month, though he shows the variations in the numbers of 

 whales through several separate seasons. 



It is interesting to note that, according to the above account of the fluctuations in the 

 catches, one must suppose that during the greater part of the season the tendency is 

 either for whales to leave South Georgia to go further south, or to arrive at South 

 Georgia from the direction of the equator. Similarly among the catches at Saldanha 



