238 | ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
the growth rate and ages of whales, and since there are now some 
5,000 marked whales at large in the Southern Ocean, it is expected that 
new evidence in this connection will be obtained in the future. 
II. DISTRIBUTION AND MIGRATIONS OF THE SEPARATE SPECIES 
The Mystacoceti, or whalebone whales, include the following 
species :? 
BALAENIDAE (right whales) : 
Balaena mysticetus Linnaeus. Greenland right whale. 
Hubalaena glacialis (Bonnaterre), H. japonica Lacépéde, HB. australis Des- 
moulins, ete. Black right whales. 
Neobalaena marginata Gray. Pigmy right whale. 
BALAENOPTERIDAE (rorquals, ete.) : 
' Megaptera nodosa (Bonnaterre}) (=M. novaeangliae (Borowski) ). Hump- 
back whale. 
Balaenoptera (=Sibbaldus) musculus (Linnaeus). Blue whale. 
B. physalus (Linnaeus). Fin whale. 
B. borealis Lesson. Sei whale. 
B. brydei Olsen. Bryde’s whale. 
B. acutorostrata Lacépéde. Lesser rorqual or minke. 
RACHIANECTIDAE: 
Rachianectes glaucus Cope. Gray whale. 
These whales are primarily inhabitants of the colder regions, and 
although most of the species visit temperate and even tropical waters, 
the largest numbers are seen in comparatively high latitudes. All 
the species, so far as is known, undertake more or less extensive 
seasonal migrations (though some species travel considerably greater 
distances than others), and thus an account of their distribution must 
include an account of their migrations. In winter the majority move 
into relatively warm waters, and this is the season in which breeding 
for the most part takes place. In summer the main herds move into 
colder waters where planktonic crustaceans offer an abundant food 
supply. In those species, whose feeding habits have been adequately 
investigated, it is found that very little food is taken in the warm 
waters in winter, and the migrations are thus linked with an alter- 
nation of feeding and breeding which is a specially important aspect 
of the general biology of whales. 
Although a few whalebone whales (usually humpbacks) occasion- 
ally migrate as far as the Equator, there can be very little interchange 
of stock between the two hemispheres, and they may be regarded as 
separated by the equatorial regions into a northern and a southern 
population. The blue, fin, sei, lesser rorqual, and humpback whales of 
the Northern Hemisphere are regarded as the same species as their 
2Dr. F. C. Fraser, of the British Museum (Natural History), has kindly advised me on 
the nomenclature. 
