WHALEBONE WHALES—MACKINTOSH 245 
however, that the grouping becomes more distinct toward the end 
of the summer. Rayner (1940) has shown also, through the recovery 
of whale marks, that there is some interchange of blue and fin whales 
between one group and another. 
In winter a few blue whales (mostly small and immature) are taken 
off the West African coast as far north as the Congo, in the Indian 
Ocean up to Madagascar and northwest Australia, and off the west 
coast of South America as far north as Peru and Ecuador, but it is 
evident that these shore stations do not tap the main stock, and it is 
no doubt for that reason that no blue whale marked in the Antarctic 
has been captured in the warm latitudes in winter. The assumption 
that they migrate into warmer waters in winter is based on analogy 
with other species such as the humpback; on the fact that they are 
not hunted in warm waters in summer or cold waters in winter; on 
changes in the local composition of the catches (see Harmer (1981), 
Mackintosh (1942) and others) ; on variations in fatness which sug- 
gest movements to and away from the rich feeding grounds in cold 
waters (Mackintosh and Wheeler, 1929); and on the incidence of 
parasites and scars which are believed to be contracted only in cold 
or in warm waters (Hjort, 1920; Bennett, 1920; Harmer, 1931; Hart, 
1935; etc.). The evidence is all circumstantial, but taken as a whole 
it leaves little doubt that there is at least a general tendency to move 
toward the Equator in winter, and the Poles in summer. 
Tt is unlikely that the main stocks of blue and fin whales move in 
a body into tropical waters, for no large numbers of them are recorded 
as having been seen there. In summer the majority seem to be concen- 
trated in high latitudes in a comparatively restricted zone, but in win- 
ter it is possible that they are dispersed over an area more than 10 times 
as great, and extending from the ice edge perhaps to subtropical re- 
gions. If winter concentrations are formed they must presumably 
keep south of the principal shipping routes. 
In the Northern Hemisphere blue whales are recorded from Spitz- 
bergen to the Bay of Biscay, from west Greenland to New England, 
and from Alaska to south California and Japan and Korea (Harmer, 
1928; G. M. Allen, 1916; Hjort and Ruud, 1929; etc.). The evidence 
for their migrations is similar to that in the south. Kellogg (1929) 
shows that a seasonal migration is confirmed by the statistics of 
catches, and the matter is further discussed by most authors who have 
visited northern stations or analyzed the statistics of catches (see 
above under Introduction). Little, however, is known of the detailed 
movements of the northern blue whales. Collett (1912) suggests that 
in the North Atlantic they spend the winter in the open ocean between 
the North American coast and the Azores, and move up into Arctic 
latitudes between Europe and Greenland in summer. 
