3 88 DISCOVERY REPORTS 



the Antarctic of course much greater numbers of whales have been taken than in the 

 warmer waters, and the catching has on the whole been more continuous. 



These are the outstanding differences between the major divisions of the whaling 

 grounds, but for a consideration of the relative effect on the stock of whaling in these 

 different regions a rather more detailed comparison is needed. Although there is almost 

 complete information on the numbers of each species taken at each whaling centre, 

 there is unfortunately very little information on the proportions of different sexes, sizes 

 and other classes of whales in the winter catches at tropical and subtropical stations. 

 Some fuller details have appeared in the more recent numbers of the International 

 Statistics, but only those referring to the 1937 season give the details at a sufficient 

 number of winter stations to provide a useful comparison. Table 29 is based on these 

 statistics and includes particulars of the preceding Antarctic summer season (1936-7). 

 This table is to be read with a good deal of reserve, for some of the figures are mis- 

 leading. The proportions of the species, although valid for 1937, are not representative 

 of the catches in general, for Table 10 clearly shows that at many localities the propor- 

 tions of the species in the catches have changed considerably. The yield of oil per Blue 

 whale unit, for reasons given on p. 208, cannot be taken as strictly comparable for dif- 

 ferent places where the constitution of the catch is different. Other figures, such as the 

 sex ratio, etc., are in some cases based on an inadequate number of whales. Finally, the 

 average lengths and percentage of immature whales are based on whalers' measurements 

 which one cannot expect to be wholly accurate. However, this table is instructive where 

 there are outstanding differences in the figures and where it can be checked with 

 Table 10 and with previous results of the Discovery Committee's observations. 



It is seen that the yield of oil is highest in the Antarctic pelagic whaling and lowest at 

 the subtropical stations. The cause of this might be simply that the average size of the 

 whales is less at the latter, but it must be supposed to be due in part to the poorer con- 

 dition of the whales. Mackintosh and Wheeler (1929, pp. 364-72) showed that at 

 Saldanha Bay, although the large whales which had recently arrived from the Antarctic 

 feeding grounds were in good condition, the small whales, which made up a much 

 greater part of the catch, had thinner blubber than whales of the same size at South 

 Georgia. The comparatively high yield at tropical stations would be explained if most of 

 the Humpbacks are taken there before they have lost condition, or if z\ Humpbacks are 

 in reality equivalent to rather more than one Blue whale (see p. 208). 



The percentage of immature whales is almost everywhere higher and the average 

 length lower in the tropical and subtropical centres than in the Antarctic. This fact has 

 often been commented upon. The percentage of immature Blue and Fin whales at 

 South African stations is especially high, but the percentage of immature Humpbacks 

 at tropical stations is not much more than in the Antarctic. There is a high percentage 

 of immature Humpbacks at subtropical stations, but here the species is taken in insigni- 

 ficant numbers. 



For the sex ratio a better standard of comparison is provided in Table 22, p. 268. 

 On p. 267 it was remarked that, although the sexes of each species are approximately 



