WHALEBONE WHALES—MACKINTOSH 243 
most part separated at both ends of their migration routes, and be- 
tween which there cannot be very much interchange. 
The information given by Harmer (1928), Townsend (1935), and 
the International Statistics shows that in the Northern Hemisphere 
humpbacks have been found from the Cape Verde Islands to Spitz- 
bergen, from the West Indies to Baflin Bay, from Mexico to the Bering 
Sea, and from the Mariana Islands (15°-20° N.) to Kamchatka. 
Again they were hunted in tropical waters in winter and in high lati- 
tudes in summer, and this and the evidence assembled by Kellogg 
leave little doubt that their migrations here are similar to those in 
the Southern Hemisphere. It is noteworthy, however, that in the 
north the oceans are relatively restricted in high latitudes, so that the 
Hast and West Atlantic stocks and the East and West Pacific stocks 
may mingle when they migrate poleward in summer. It may be, how- 
ever, that the populations of the North Atlantic and North Pacific 
form two entirely separate communities. 
(5) Balaenoptera musculus 
The blue whale is the largest of all species, reaching a maximum 
length of approximately 100 feet, and although not so numerous as 
the fin whale it is the most valuable to the modern whaling industry. 
The “blue whale equivalent,” which compares the average production 
of oil from different species, is taken as 1 blue=2 fin=214 hump- 
back=6 sei. The various species of Balaenoptera are very similar in 
form, and are difficult to distinguish from one another in the water 
except by the shape of the dorsal fin. Out of the water, however, they 
are readily distinguished by the pigmentation, the blue whale having 
a mottled bluish-gray skin with white flecks over part of the ventral 
surface. 
The blue whale is a widely distributed species. The same may be 
said of the fin whale, and since the distribution of the latter species 
is very similar to that of the blue, it will be referred to from time to 
time in this section. Blue and fin whales are more strictly oceanic 
species than humpbacks, for they are not concentrated in coastal waters 
at any time of year. In the Southern Hemisphere they occupy in 
summer a circumpolar zone in Antarctic waters (well shown in Han- 
sen’s Atlas, 1936) which, for at least a large part of the season, is 
continuous in the Atlantic, Indian Ocean, and Australian sectors, and 
almost certainly continuous also in the Pacific sector. There is some 
tendency, however, to concentration in certain regions. Hjort, Lie, 
and Ruud (1932-38) have shown that the yearly distribution of the 
whaling fleet indicates a tendency for the blue and fin whales to be 
