268 DISCOVERY REPORTS 



stock may breed once in three years. A possible mean figure of once in two and a half 

 years is suggested. 



6. The annual increment of corpora lutea in the ovaries of the whole adult catch is 

 discussed. Whales from 78 to 8 1 ft., a group which there is reason to suppose is a year 

 group of newly mature whales, are found with an average of 1-91 corpora lutea. There is 

 evidence that in subsequent years the increment is 1-13. 



7. The corpora lutea frequencies furnish indications which support paragraph 6. 

 Prominent features of the graph of frequencies are found to move up by slightly more 

 than one corpus luteum in one year and proportionally in two years. 



8. A tentative correlation between age and number of corpora lutea is thus established. 

 The results suggest that whales over two and under three years old are found with two 

 corpora lutea ; subsequently there is an increase of eleven corpora lutea for every ten 



years. 



9. There is evidence which suggests the homogeneity of the adult female population 

 all over the present pelagic whaling grounds. 



10. Physical maturity will thus be attained at ten to eleven years of age. 



11. The oldest females taken (1934), regarded as of the order of thirty years of age, 

 show no sign of diminishing fertility, possibly because under present conditions Blue 

 females are unable to survive long enough to reach a climacteric. 



12. Examination of the age distribution of the population of adult Blue females 

 suggests that there has been a progressive diminution in the rate of recruitment of 

 recent years. The present rate is thought to be insufficient to maintain the stock of 

 Blue whales under the present intensity of whaling operations. 



13. The method of presenting average lengths adopted by Hjort, Lie and Ruud in 

 Hvalrddets Skrifter is criticized. In a revised form the average lengths of females taken 

 in the last five years has fallen from 82-36 (1 930-1) to 78-99 ft. (1935-6). Blue females 

 are thus caught on the average before they have had time to reproduce at all. 



14. Another aspect of the situation described in 13 above is the increase in immature 

 whales caught. This again is shown in a revised form preferred to the Norwegian 

 presentation. Over 41 per cent of the total catch of females in 1935-6 consisted of 

 immatures. 



15. The evidence above all points to the acute hardship which is being suffered by 

 the stock of Antarctic Blue whales. The stock is already seriously depleted and further 

 hunting on the same scale bids fair to make Blue whales so scarce that they will cease 

 to be a source of profit to the industry and so diminished in numbers that the stock even 

 if completely protected may take many years to recover. 



