Sea Bird Distribution— KURODA 
59 
TABLE 2 
Population Densities of Sea Birds in the Subdivisions of the "Northern Sea Divisions’’ 
SEA AREAS 
NUMBER 
OF BIRDS 
OBSERVED 
PER DAY 
NUMBER 
OF 
SPECIES 
OBSERVED 
NUMBER 
OF BIRDS 
PER HOUR 
(AT 7 MILES) 
NUMBER 
OF BIRDS 
PER SQUARE 
MILE 
W. Bering Sea 
38 
8 
7 
7.42 
Attu-Commander Is... 
307 
10 
40 
49.11 
In Transit 
112 
8 
17 
21.19 
Offshore S. Kamchatka............. 
280 
9 
50 
59.81 
Data on 10 chief species of birds recorded in 
the Northern Sea Division are analyzed in 
Table 3 and Figure 2. The mean economic 
density roughly represents the general specific 
density, but by inclusion of some concentrated 
and irregular densities, the species’ most fre- 
quent density, the mode, is obscured (Table 
3). In the Tubinares ( Fulmarus glacialis, Puf- 
finus tenuirostris, and Oceanodroma fur cat a) the 
range of observed densities is very wide, be- 
cause they usually occurred sparsely during the 
day and often formed a large feeding flock, 
especially in the early morning. ( 0 . leucorhoa 
was an exception, but its chief concentration was 
outside of this sea division. ) These two patterns 
of distribution were well marked, as shown in 
Figure 2A; the most frequent densities of usual 
sparse distribution (the mode) were 1-3 birds 
per hour, while the concentrated densities (the 
"highest density’’ of Elton) were as high as 
30-70 birds per hour. In other sea birds, such 
as alcids and gulls, such a "highest density” con- 
centration was not found. But their numbers 
increased (Fig. 2B; June 23, July 2-5, etc.) 
when they were found among a mixed commu- 
nity, with porpoises and perhaps some fishes 
under the water feeding upon euphausids. The 
dominant birds were Fulmarus glacialis and/or 
P. tenuirostris. One such fulmar-dominated con- 
centration was found close to a mother ship 
(6,000 tons) of the Japanese salmon fishery, on 
July 4-5. 
Puffinus tenuirostris birds are migrants from 
the southern hemisphere and Fulmarus was 
represented perhaps chiefly by a nonbreeding 
population. Some breeding adults (a bird with 
large ova was collected), as well as some molt- 
ing young of Lunda cirrhata, were found as far 
as 200 miles offshore, and they were distributed 
rather uniformly, with a density of 1-3 birds 
per hour. But a species of Uria seemed to be 
less pelagic in distribution and only a sparse 
peripheral population was encountered, since the 
usual densities were 0. 1-0.2 birds per hour. Rissa 
spp. are gregarious pelagic gulls, but apparently 
only some nonbreeding birds were found, inas- 
much as their distributional pattern was sparse 
and irregular. 
DIVISIONS OF SEA ZONES 
The cruise track of the "Geizan,” No. 8, and 
the sea divisions traversed, are shown in Figure 
1. Oceanographic conditions (Kuroda, 1955) 
and sea bird distribution in each division and 
subdivision are briefly given below (see also 
Figs. 1, 3, and Table 4). 
A. Cold Current Sea Surface 
From the northern seas the cold current 
stretches along the Kuriles (at least to 100 miles 
offshore) south to Hokkaido. The dominant 
species of sea bird was Fulmarus glacialis. Other 
generally distributed species were: Puffinus 
tenuirostris (rare along the Kuriles), Lunda 
cirrhata, Oceanodroma fur cat a (rare off the cen- 
tral Kuriles and southward), and O. leucorhoa 
(rare in the northern seas). 
1. Northern sea division 
North of about 50° N. latitude. The air and 
water temperatures were most often 5°-6° C. 
and 8°-10° C. respectively. At night water 
temperatures often fell to 5° C. Zoogeo- 
graphic species characteristically not found 
southward were: Rissa hrevirostris (see its 
