THE SPERM WHALE 



157 



those months when the catch of Blue and Fin whales off Natal is greatest. Fig. 66, 

 showing the total monthly catches of Sperm whales for seasons 1925, 1926 and 1928 and 

 of Blue and Fin whales for seasons 1922 and 1930, brings out this point clearly. It is, 

 therefore, quite possible that the true state of affairs would be represented by even 

 unimodal curves taking their origin in March showing a peak in August and a return to 

 zero in January. If the drop in the curve at the end of the year indicates a movement 

 towards the south, it will be seen by reference to Figs. 42-43 that the main pairing season 



300- 





L 

 0) 



200- 



100- 



— Sperm Whales 1925,6 8c 8 

 --Fin Whales I9?2&30 

 ■—Blue Whales B22&30 



Mar Apr Mai^ Jun Jul Aug Sep Oct Nov Dec Jan 

 Fig. 66. Catches of Sperm, Blue and Fin whales. Natal. 



is during this southern journey, and that the chief time for parturition occurs when the 

 whales are to the south of Natal, and that both seasons are practically over before the 

 return migration in the following March, April and May. If this really is so, it forms a 

 striking contrast to the Whalebone whales in which the breeding migration takes place 

 in the opposite direction towards the north; but it must be remembered that the 

 southern movement of Sperm whales may merely be a spreading of the population from 

 warmer waters where large numbers may remain, so that parturition may be occurring 



