2?8 DISCOVERY REPORTS 



As Laurie points out (1937, p. 232) this is likely to result in a few whales being included 

 which have recently ovulated without becoming pregnant. In 100 ovaries with func- 

 tional corpora lutea, however, there were only four in which he could find no foetus, and 

 it is not impossible that even in these a small foetus was present. Thus the percentage 

 may be a little too high but should be very nearly correct. In both the pelagic figures 

 and those from South Georgia a number of seasons are combined which are not perhaps 

 strictly comparable, for they do not always cover quite the same period of months, and 

 there is some evidence that the percentage pregnant has altered from year to year (see 

 p. 223). The calculated percentages, however, must be reliable at least as a rough 

 indication of the change which takes place. It is noteworthy that the catching of females 

 accompanied by calves was prohibited during most of the period covered by the pelagic 

 data, but not during the period covered by the South Georgia data. 



The table shows that there is a substantial decline in the percentage of pregnant 

 females in the catches of both species on the pelagic grounds and at South Georgia, and 

 this must reflect a real change in the composition of the population. This must imply an 

 increasing proportion of resting whales, though at South Georgia it may be balanced 

 partly by an increase in lactating females. It is difficult to know whether the decline is 

 primarily attributable to earlier departure of pregnant females from the whaling grounds, 

 or later arrival of other adult females. 



THE STOCK OF WHALES 

 EVIDENCE OF THE DEPLETION OF THE STOCK 



Since no direct method has yet been found for making reliable estimates of the actual 

 numbers of whales in the southern populations the effect of whaling on the stock must 

 be mainly judged by changes in the size and composition of the catches. It is generally 

 admitted that the stocks at least of Blue and Humpback whales have substantially de- 

 clined, and the evidence for this is to be found in the observed scarcity of certain species, 

 in the absolute or relative reduction in the catches, and in the reduced sizes and ages of 

 the whales caught. 



The statistics of the Antarctic catches have been exhaustively studied from year to 

 year by Hjort, Bergersen, Lie and Ruud. They point out that differences in the catches 

 between one year and another are the result not only of changes in the stock, but also 

 of changes in the number and efficiency of the ships, in the limits of the whaling season, 

 in the regulations protecting certain classes of whales, in weather conditions, etc., and 

 they show that the best method of comparing the catches at different times and in 

 different places is to calculate the catch per catcher's day's work, a figure which elimi- 

 nates at least some of the variable factors. They discuss the significance of progressive 

 changes in the composition of the catches, and reference should be made to their series 

 of articles for a general commentary on the prospects of the whaling industry year by 

 year in relation to the stock of whales. 



Perhaps the most convincing evidence of the decline of the Blue-whale stock is to be 



