448 DISCOVERY REPORTS 



females in the catches at South Georgia and on the pelagic whaling grounds. The South Georgia figures 

 are based on the biological investigations made during the period 1925-31, and the pelagic figures 

 are from 1939-54 ( see Table 25, 'Percentage lactating'). Both samples relate to times and places 

 at which the taking of females accompanied by calves was prohibited. The pelagic sample relates to 

 the 5 months December-April, and the overall proportion of mature females found to be lactating is 

 3-3 ± 1-08 % ; during these 5 months at South Georgia the proportion lactating was 18-9 ±4-3 %. While 

 it is possible that the enforcement of this prohibition was less rigorous at South Georgia in 1925-31 

 than in British pelagic expeditions from 1939 onwards, it seems possible that such a great difference 

 in the incidence of lactating females in the catches reflects a real difference in the proportion of 

 lactating females in these two populations. If true it would mean that lactating females appear in 

 South Georgia waters in relatively greater numbers than on the pelagic whaling grounds further south. 



So far we have expressed the occurrence of lactating females in the catches as a percentage of the 

 total mature females. This is open to the criticism that lactating females are protected to a degree 

 which may well vary with time and place. Text-fig. 50 at first gives the impression that the peak influx 

 of lactating females is later in South Georgia waters than on the pelagic whaling grounds, but this is 

 misleading. It is possible to obtain a much more accurate impression of the seasonal and numerical 

 incidence of lactating females on these two whaling grounds, by applying the percentage figures for 

 lactating females to figures of the total catches of mature females, and thus to obtain estimates of the 

 numbers of lactating females in the catches in different months. The method is similar to that employed 

 when examining the numbers of recent ovulations in antarctic waters (p. 440). The same figures are 

 used for the percentage immature and the source of the data on percentage lactating is given above. 



The basic figures used for the catches are for the period 1927-35 for South Georgia (as before) and 

 1945-47 for the pelagic catches. Data on the latter period are used because they include catches made 

 in December and April. The results are presented in Table 25 and Text-fig. 51, and are to be regarded 

 as approximations for demonstration purposes rather than as precise values. Thus the validity of the 

 early and late catches cannot be checked but should not affect the main conclusions. 



Table 25. Estimated monthly frequencies of lactating females in the catches at South 

 Georgia and on the pelagic whaling grounds 



South Georgia, eight seasons 1927-35 



Pelagic, two seaso?ts, 1945-47 



In Text-fig. 51a curve has been drawn which shows the expected monthly incidence of weaning. 

 This curve is the same shape as the curve of calving frequencies (Text-fig. 31), but is displaced in time 

 by about seven months, so that the mean value occurs in December (as estimated above), and the 

 mode is, therefore, at the end of November. Differential growth between birth and weaning should 

 affect the shape of this curve, though not the mode and mean, but it has not been possible to allow 

 for this. The estimated numbers of lactating females in the catches are shown in the same figure for 

 comparison. It will be seen that peak numbers of lactating females were taken in South Georgia 



