GENERAL CONSIDERATIONS 339 



the ages estimated from the ovaries and from the ear-plugs of a series of female fin whales. The value 

 of this evidence depends on the completely independent nature of the two lines of work and for this 

 reason and because they were not available when the work was carried out the ear-plug data will not be 

 used in the first part of this paper. 



Migrations 

 The growth-rates and mature sizes of northern and southern hemisphere fin whales are very different 

 and the average annual cycle is 6 months out of phase, so we can take it that there is no important 

 degree of interchange between them (Omura, 1950; Jonsgard, 1952; Pike, 1953), but the animals in 

 both hemispheres do undertake long seasonal migrations. Kellogg (1929) summarized what was then 

 known about the migrations of baleen whales. Most of this evidence relates to whales seen on passage 

 in the northern hemisphere and reveals a movement from low to higher latitudes in spring and a 

 return movement in the autumn. Mackintosh (1942) has also discussed the evidence for these migra- 

 tions and concludes that it ' can leave no doubt that there is a general tendency for Blue and Fin whales 

 to undertake long annual migrations between the Antarctic and temperate or tropical waters, though 

 this is not to say that the Antarctic is completely deserted in winter or the warmer waters in summer ' 

 (p. 250). The humpback whale is a coastal species and migratory herds may regularly be seen from 

 the coasts (Chittleborough, 1953 ; Dawbin, 19566). In the longitude of New Zealand the main herds 

 are said to leave antarctic waters in early May, to reach 46 S. by mid-June, and to arrive at the 

 breeding area at latitude 15 S. by mid-August. 1 On the return migration they reach 46 S. by early 

 November and arrive at the feeding area about 66° S. by mid- to late December. The vanguard and 

 rearguard reach the respective latitudes approximately 6-7 weeks earlier or later than the main group 

 (Dawbin, 1956, p. 193). The fin whale is not a coastal species so direct observations of migrating 

 animals are few and most of the evidence is circumstantial, but we may also reasonably draw analogies 

 with the humpback whale. Some direct evidence comes from whale marking ; 22 humpback whales 

 marked in the antarctic were recovered off north-west Australia (Rayner, 1940), and a further nine 

 in recent years, but so far there are only two marked fin whales to demonstrate the migration. 2 One 

 marked in the antarctic in 64 52' S., 22 30' E. in February was recovered off Cape Province, South 

 Africa, 33 04' S., 17 50' E. at the end of June 2 years later (Rayner, 1940); another was marked in 

 October off the coast of Brazil in 28 03' S., 46 17' W. and recovered after 11 years near South 

 Georgia in 52 55' S., 38 42' W. (Brown, 1954) 2 . Rayner and Brown established, as a result of marking 

 returns, that these whales tend to return to the same antarctic locality and are partially segregated in 

 certain broad areas though there is some lateral dispersal. 



The indirect evidence comes from a number of sources. There is an important reference by Morch 

 (191 1) to the occurrence of great numbers of fin whales along the Brazil coast, between 12 and 18 S. 

 latitude every year from May to November, but this has not been confirmed. It is significant that 

 whaling operations in the Antarctic have been largely confined to the period October-April with the 

 largest catches obtained from December to March. In low latitudes off South Africa catches are 

 made in the period May-October. This indicates that the bulk of the population spend the winter 

 months in lower latitudes, and the summer in the Antarctic, but at one time catching was carried on 

 throughout the winter at South Georgia, so not all migrate north in the autumn. Recently Brown 

 (1957, p. 163) has found that 'not all rorquals go south for the southern summer and it may be that 

 more than was thought either miss the southern migration altogether, or get out of step with the main 

 migration movements'. 



1 Chittleborough's work suggests mid-July off West Australia. 



2 Later mark recoveries have confirmed the humpback movements and Brown (1959, i960) gives details of five addi- 

 tional fin whale recoveries. 



