246 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
(6) Balaenoptera physalus 
The fin whale is second in size to the blue, the maximum length being 
about 85 feet, though specimens over 80 feet are rare. It is by far 
the most abundant of the large whales, and it is the species on which 
the modern whaling industry mainly depends. It is distinguished by 
the coloring which is a plain bluish gray on the back and flanks and 
white on the ventral surface. The coloring is asymmetrical, the dorsal 
pigment apparently invariably extending farther down on the left 
than on the right flank. 
The above description of the distribution of blue whales applies in 
almost every particular to fin whales, but some minor differences are 
as follows. In the catches of the tropical land stations fin whales are 
generally even scarcer than blue whales, and it seems likely that they 
do not normally penetrate so far into tropical waters in winter as 
the latter species. In summer they tend to keep a little farther than 
blue whales from the coldest water at the edge of the pack ice. It 
would appear, therefore, that the range of the fin whale migration is 
rather less than that of the blue whale, though we cannot be certain 
of this. In the Antarctic in summer they are found in all longitudes 
and they show a slight tendency (rather less definite than in blue 
whales) to concentrate in the areas distinguished by Hjort, Lie and 
Ruud. The evidence of migration is similar and perhaps a little 
firmer. There is one record of a fin whale caught off the African coast 
which had been marked in the Antarctic. Other marking records 
show that fin whales usually, but not always, return to the same part 
of the Antarctic after the winter migration. It seems that fin whales 
mostly arrive in Antarctic waters later in the summer than blue 
whales, for in the catches of the whaling fleet the proportion of fin 
whales is small in spring (October-December) but rises sharply about 
the end of December. 
(7) Balaenoptera borealis 
The sei whale is smaller than the fin, with a maximum length of 
about 60 feet. The pigmentation is not dissimilar, but the whitish 
area on the ventral surface is less extensive. The whalebone plates 
are short as in other rorquals, but resemble those of the right whales 
in the fine texture of the plates and bristles. 
This species inhabits warmer waters than blue and fin whales, and 
there seems little doubt that it undertakes seasonal migrations 
(Matthews, 1938b; Kellogg, 1929; Andrews, 1916; and others) , but be- 
yond this not very much is known for certain. It is scarce in the Ant- 
arctic except at South Georgia where the water is relatively warm. 
Here it sometimes appears in substantial numbers in late summer. 
Matthews points out that large catches of sei whales may sometimes 
