the ground they occupied. His work and that of naturalists who followed 
him is summarized by Jordan (1898, part 1, p. 88) and by Hanna (U. S. 
Bureau of Fisheries, 1917, p. 111). Attempts to estimate seals have 
always been handicapped by the rough terrain and the prevailing misty 
weather on the Pribilof Islands. 
The development of aerial photography and the construction of 
an air field on St. Paul Island in 1943 brought hope that a new census 
method might be developed. Several opportunities to photograph sample 
rookery areas from the air were offered at various times by visiting 
planes (appendix G). In 1948 a Fish and Wildlife Service twin-engine 
plane equipped with an aerial camera was flown to the islands. All 
rookeries were photographed. Of the 376, 7x7-inch negatives produced, 
about 100 were found useful in calculating the pups per unit of rookery 
area. 
The negatives were not sharp enough to permit a count of 
individual seals, but they did show the outline of massed seals on the ~ 
rookeries (fig. 12). The technique was as follows: (1) On photographs, 
with the help of a planimeter, the biologists were able to measure the 
dark patches representing areas occupied by seals. (2) They then counted, 
on foot, the living and dead pups on 6 sample rookeries. (3) They 
wt 

rookery. This illustrates the definite outlines of the breeding 
area at the height of the season. Bering Sea in foreground; 
harems in the middle; bare ground with thinly scattered idle 
bulls at top; an elevated walkway at left. Photo taken from an 
altitude of 1,000 feet on 14 July 1948 (VBS and KWK aerial photo 
29). 
-26- 
