94 THE FUR SEALS OF THE PRIBILOF ISLANDS. 
though the actual population has been diminished by the more frequent and pro- 
longed absence of the cows. The number of bulls therefore found for those two 
rookeries on July 31 can not be accepted as representing the number of families in the 
breeding season and must be reduced. 
CORRECTIONS ON ST. PAUL. 
The need for revision in the census of St. Paul Island is not so great; but our 
experience during the past season shows that in all probability the harems on Zapadni 
and Tolstoi rookeries were slightly overestimated and those on the main part of 
Polovina underestimated. 
Zapadni rookery occupies a long gradual slope back of the more abrupt bowlder 
beach. This slope was filled with savage bulls, making close approach in 1896 impos- 
sible. The count of harems was made from a boat offshore and was not corrected by 
a count from behind. From this point of view of the water the whole field could not 
be inspected, and the figures of last year were felt to be merely a rough approximation. 
The estimate for those not clearly seen was certainly too large. This year the rookery 
had shrunk so largely that observation points from the rear, commanding the entire 
breeding ground, could be reached. In like manner the estimate of Tolstoi for 1896 
was made under difficulties, which were more satisfactorily overcome in 1897. 
On Polovina the conditions were similar to those on Zapadni. The main part of 
the rookery lies on a gradual even slope, behind which the idle bulls were coflected in 
such numbers as to prevent near approach, while there was no opportunity to inspect 
the rookery from the water. This year the conditions were so changed as to permit 
of much closer inspection, and although the mass of breeding seals had plainly 
shrunk at every point, practically the same number of harems were counted, making 
an addition of harems necessary. 
SIVUTCH ROCK. 
A third correction must be made in the estimate of Sivutch Rock. The original 
estimate of this rookery was made after an inspection of the rock with a field glass 
from the plateau of the Reef, which showed 27 bulls in charge of harems on the 
northern face. At the time of the count of dead pups in August a landing was 
effected and an attempt made to estimate the number of harems, as the rookery 
seemed plainly greater than our original estimate allowed for. Sixty-seven bulls 
occupying harems were then found, though it was plain that the rookery was wholly 
disorganized. This season Sivutch Rock was inspected from all sides in a boat at 
the height of the season and an adequate notion of the extent of the rookery obtained. 
Harems were found on the southern side and in places where their presence was not 
suspected in 1896. The total number counted in 1897 was 102. It is therefore 
necessary to largely increase the original estimate for this rookery. 
In balancing these under and over estimates, however, they practically neutralize 
each other and leave the total for St. Paul for 1896 about what it was. For St. George 
Island also the difference resulting from the revision is not great, being only about 600 
cows. 
THE IMPORTANT CORRECTION IN THE CENSUS OF 1896. 
But the chief error in the census of 1896, and this applies to both islands, lies in 
the percentage of correction to be added for absent cows. This has already been 
