264 



DISCOVERY REPORTS 



maximum in February, was the main feature of the second half of the season. The 

 distribution of Fin whales in 1928-9 followed a similar course, but the increase in pro- 

 portion of immature whales evidently began earlier, and was more diffuse, though the 

 maximum occurred in the February of that season also. With regard to Fin whales, 

 conditions in 1930-1 were evidently abnormal, an unfortunate circumstance, as it was 

 during this season that the most detailed examination of the diatom film was under- 

 taken. Even in that year, however, there was a marked increase in the proportion of 

 immature whales during the second half of the season, which was, it will be noted, a 

 very poor one from the whalers' point of view. The examination of the maturity data 

 showed that, during the three seasons studied, there was a marked increase in the pro- 

 portion of immature whales killed as compared with seasons 1924-5 to 1926-7, for 

 which figures were obtained by Mackintosh and Wheeler (1929, p. 468). They found 

 the proportions of immature Fin whales killed to be 22-3 per cent of the males and 

 27-5 per cent of the females. During seasons 1928-9 to 1930-1 these figures increased 

 to 3 5 "3 and 31-4 per cent respectively, increases of 13 and 3-9 per cent. In the first 

 period the excess of male over female Fin whales captured, 8-46 per cent, was due 

 almost entirely to mature males. In 1928-31 the excess, 4-33 per cent, was due almost 

 entirely to immature males. The percentage of immature whales taken in 1928-9 was 

 particularly high, and can be correlated with the exceptionally low percentage infection 

 with diatom film observed in that season. 



The seasonal variation in fatness of the Fin whales was closely studied, and a fair 

 degree of correlation with the diatom data found. Several factors complicate the fatness 

 statistics: excessive fatness of pregnant whales and newly weaned calves, excessive 

 leanness of immature whales and lactating females. These factors appear to cancel each 

 other when large numbers of whales are considered, but when small groups, segregated 

 according to size or sex, are selected, it becomes almost impossible to trace the correla- 

 tion with diatom film. For this reason the monthly total catch of both sexes has been 

 used, when the correlation agrees very well with the general idea of whale movement 

 gained from other sources. Owing to their small numbers during the later part of the 

 season, the Blue whales do not show this correlation at all clearly. 



SOUTH GEORGIA, 1928-9 

 September and October, 1928 

 Total whales dealt with 87, of which two were Sperm (JcJ with diatoms, the rest Blue and Fin 

 whales. Total Blue and Fin whales ... 86 



With diatoms 40 47-1% 



