294 DISCOVERY REPORTS 



Histological evidence, mainly a statistical analysis of testis tubule diameters, shows that the male 

 sperm whale has a sexual season. 



Multiple ovulation (twinning) only occurs in o-66% of foetal records. 



The sizes of two proven calves, and of the smallest whales feeding on their own account, show that 

 the mean length of the calf at weaning is about 67 m. (22 ft.). By examining the proportions of adult 

 females pregnant, lactating and resting, and by plotting dated records of whales shorter than 67 m. in a 

 figure reproducing the foetal growth curve, the nursing period is estimated at about thirteen months. 

 The female sexual cycle thus normally lasts three years (sixteen months gestation, thirteen months 

 lactation, seven months anoestrum). Rarely anoestrum does not intervene, for there are occasional 

 reports of females pregnant whilst still lactating. 



After weaning all that can be said at present about age is that recovered harpoons show that male 

 and female sperm whales can live for at least thirty-two and twenty-two years respectively. 



Females are invariably in schools but males may be in schools or solitary. Schools are discussed 

 qualitatively as juvenile, bachelor, and harem schools; and quantitatively as pods, shoals and herds. 

 At the Azores changes occur in the proportions of males schooling in successive months. 



In foetal life there are as many female sperm whales as males, and the post-natal ratio is likely to be 

 similar. Reasons are advanced for the excess of males in the Azores catches. 



The sperm whale, although an oceanic species, is believed to frequent the coasts of oceanic islands 

 (such as the Azores), perhaps because of an enhanced food supply. 



Monthly catches and sex ratios show that the Azores stock migrates. A minor fraction, virtually 

 all males, frequents the islands in winter; but the females and most of the males begin to arrive in 

 May, the stock reaching its greatest strength in July. It does not move as a body north of the Azores. 

 The main stock is believed to spend the winter to the southward, probably around the Cape Verde 

 Islands and also the Canaries. Conjectures are made regarding the migrations of sperm whales in the 

 eastern North Atlantic. 



A review of known facts about the world stocks of sperm whales finds no evidence of racial segrega- 

 tion, except for a possibility, deserving further study, that northern and southern whales differ in 

 their growth. 



Average lengths and the proportions of immature whales in the catches, and the catch per whale- 

 boat from year to year, do not suggest that the Azores stock is overfished at present; but a helpful 

 conservation measure would be a length restriction at 30 ft. (about 9 m.), designed to protect im- 

 mature females. Introduction of steam whalecatchers, unless rigorously controlled, is likely to 

 endanger the stock. In the economic setting of the Azores, whaling from open boats is an efficient 

 business and deserves to be fostered unchanged. 



REFERENCES 



Allen, G. M., 1941. Pygmy sperm whale in the Atlantic. Field Mus. nat. Hist., Chicago, Zool. ser. xxvn, pp. 17-36, text- 

 figs. 1-4. 



Barnard, K. H., 1932. Amphipoda. Discovery Reports, v, pp. 1-326, text-figs. 1-174, pi. 1. 



Baylis, H. A., 1929. Parasitic Nematoda and Acanthocephala collected in 1925-27. Discovery Reports, I, pp. 541-60, text- 

 figs. 1-16. 



1932. A List of Worms Parasitic in Cetacea. Discovery Reports, VI, pp. 393-418. 



Beale, T., 1839. The Natural History of the Sperm Whale. . . to which is added a Sketch of a South Sea Whaling Voyage. . . . 



London. 

 Beddard, F. E., 1900. A book of whales. London. 



19 1 5. Contributions to the Knozvledge of the Anatomy of the Sperm Whale (Physeter macrocephalus) based upon the 



examination of a young Foetus. Ann. Durban Mus. 1, part 2, pp. 107-24, text-figs. 1-9, pi. VIII. 



