THE SEI WHALE 



257 



GROWTH AND AGE 



The female Sei whale becomes mature shortly after reaching a length of 14 m. 

 Only six pregnant females less than 15 m. long are recorded, their measurements 

 ranging from 14-38 to 14-87 m. The smallest mature female Sei whale was 14-0 m. 

 long and had recently ovulated for the first time. There was only one corpus luteum in 

 the ovaries and no foetus was found in spite of a careful search. The majority, then, 

 reach maturity at about 14-5 m. of total length, a few between 14 m. and this length, 

 and some not until longer. Reference to Fig. 68 shows that the male Sei whale reaches 

 sexual maturity between the lengths of 13 and 14 m. and the length of 13-5 m. may be 

 taken as the average length. The smallest two males examined for sexual maturity 

 measured 14-10 and 14-15 m. respectively. In both of these, sections showed the 



Ud^ Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Mat] 



Fig. 83. Sei whale. Lengths of immature whales by months. 



tubules of the testes full of dividing cells, but smears showed only a few spermatozoa 

 in the testis and epididymis of the first, and none in those of the second. These whales 

 were evidently young adults. On the other hand, some males had not reached full 

 sexual maturity at considerably greater lengths. 



Data relating to calf Sei whales are not available, but a number of immature whales 

 of larger size have been examined. Fig. 83 is a scatter diagram of the lengths of all 

 Sei whales recorded as immature, plotted by months, and shows a definite increase in 

 length between June and April. Fig. 84 is the curve obtained by plotting the average 

 length of these immature whales by months, and if this curve is combined with that 

 of Fig. 77 on an extended time scale, the result shown in Fig. 85 is produced. From 



