THE AGE OF FEMALE BLUE WHALES 



231 



IMMATURE WHALES 

 OVARIES SHOWING 

 RIPENING FOLLICLES 



WHALES PREGNANT 

 OR HAVING OVULATED 



foetuses were of the average size for the time of year (see Fig. 3) the mothers may be 

 assumed to have conceived during the mean pairing season, which is in the middle of the 

 southern winter (July). 



The fact that the average size of the 

 transition and mature classes is larger than 

 would form an exact agreement with the 

 South Georgia estimate of length at 

 maturity does not mean necessarily that 

 the length at maturity of these whales is 

 greater. These whales were taken farther 

 south than the South Georgia whales and 

 in their southerly migration to the ice- 

 edge have traversed a wider belt of ocean 

 containing their food (Euphausia superba) 

 and may be expected to have grown 

 slightly more than those found at South 

 Georgia. All things considered, there 

 seems no reason to suppose that the Blue 

 whales taken in the extreme south differ 

 at all from those taken at South Georgia 

 in point of growth and sexual maturity. 



Some corroboration may be sought 

 from the collection of ovaries which was 

 made in 1935-6. It has been considered 

 inadvisable to try to discriminate be- 

 tween definitely immature ovaries and 

 ovaries in which ripening follicles ap- 

 peared, because of the indifferent pre- 

 servation of the material. The results are therefore shown in a different form. All 

 the ovaries which had no corpora lutea, active or recessive, are classed as immature 

 and, as before, those which showed corpora lutea are taken to have come from whales 

 definitely mature. The arrangement of these classes by length is as follows: 



Fig. 



LENGTH 



Length distribution of immature and 

 mature whales (1932-3). 



The data given above indicate the probability that some of the immature class should 

 have been included in a transition stage, and since that has not been feasible the im- 

 mature whales may appear to be unduly represented at the lengths of 80-81 ft. The 

 general indication is, however, the same. 



