2 8o DISCOVERY REPORTS 



other: their distribution is possibly random, and the apparent shifting offshore of the mean position 

 of both habits in summer is just as likely to be due to the improved conditions for sighting whales in 

 summer as to any real movement away from the coast. In regard to the schools themselves (of whose 

 composition by sex or class Fig. 1 1 gives no clue) it has earlier been suggested (p. 276) that pregnant 

 and nursery schools may be sequestered at a greater distance from the coast than other sorts of schools. 

 McBride & Kritzler (1951) observed that captive females of the bottlenosed dolphin, in late pregnancy 

 and in parturition, segregated themselves from other dolphins in their tank. 



Jan. Feb. Mar. Apr. May. Jun. Jul. Aug Sep Oct. Nov Dec. 



Fig. 1 1 . Distances from the coast of schools and lone males sighted from Fayal and Cais do Pico 

 month by month in 1948. — Schools. °. Lone males. 



SEX RATIO 



There is no reason to suppose that one sex outnumbers the other in sperm whales, but males clearly 

 predominate in the catches at the Azores. 



Since females are small and (elsewhere than the Azores and Madeira) are widely protected, the world 

 catch figures of sperm whaling are no guide to the natural sex ratio in the sea. Among the quite small 

 sample of forty-two foetal whales examined at Horta between 1949 and 1954 there were seventeen 

 males (Table 21, p. 268). Mizue & Jimbo (1950, p. 120) found 46-2% of males among 535 foetuses 

 from the North Pacific: the International Whaling Statistics, for seven seasons of Peru whaling 

 between 1937 and 1951, show 53-1% males among 944 foetuses. When these counts for the North and 

 South Pacific are combined, the sexes are found to be equal in foetal numbers, the proportion of males 

 being 50-57%. It appears therefore that in foetal life there are as many female sperm whales as there 

 are males. The foetal sex ratio is not necessarily the same as the post-natal ratio, but it is worth men- 

 tioning that the old-time sperm whalemen (whose experience was world-wide) maintained that in 

 post-natal animals the females outnumbered the males (Wilkes, 1845, v, p. 528). 



One thousand three hundred and seventy-nine sperm whales were caught at Fayal between 1939 

 and 1954 and 64-6% were males (Table 28). As may be seen in Table 28, the sex ratio of caught whales 

 at Fayal fairly closely reflects the ratio in the catch from the whole archipelago: in the period 1948-54 

 there were 69-3% of males in the Fayal catches and 68-82% in the catch from the Azores. The monthly 



