400 



350 



300 



100 



50- 



2 4 6 8 10 i'2 



Height of sea (feet) 



Figure 5,--Sea lion piipulation-lieiKlit of ocean swell 

 relation, Chernabura Island, 1958. 



The variation in the counts, i.e., seasonal 

 and diurnal changes, and the difficulty in 

 identifying all of the animals in the photos, 

 indicate that the counts are minimal estimates 

 of the total population. 



Total Population Estimate 



A minimum estimate of the total population 

 can be obtained by summing the results shown 

 in tables 1 to 6 of the most complete surveys 

 made when the sea lion populations on land 

 were high (table 9). 



The three districts. Prince William Sound- 

 Kenai, Kodiak Island, and Shumagin-Cold Bay, 

 were all surveyed during late June 1957, 

 excluding the possibility of any duplication in 

 counts because of migration between rookeries 

 there. The Eastern Aleutian Islands survey 

 took place about 3 months later at a time 



when the total counts of the Kodiak and 

 Shumagin Islands areas were slightly below 

 the June peak but not enough below to indi- 

 cate any significant migration. The two minor 

 districts, Chignik and Bristol Bay, were sur- 

 veyed in spring and fall respectively. 



No aerial survey was made of the sea lion 

 herds of the Aleutian Islands west of longitude 

 170 W. However, visual counts and estimates 

 were made of a few rookeries and hauling 

 areas by crews of tagging vessels from the 

 Fisheries Research Institute that were op- 

 erating in the North Pacific Ocean and the 

 Bering Sea (table 10). These counts, which 

 total 4,595, include only a fraction of the 

 islands inhabited by sea lions, and the total 

 population is certainly much larger. 



The scientific leaders of the tagging ves- 

 sels estimated the total number of sea lions 

 in the Western Aleutian Islands at 40,000. 

 In May 1959, Kenyon and Rice (1961) sur- 

 veyed the same area and estimated 44,630 

 animals. They made a survey of the Eastern 

 Aleutian Islands in March 1960 and estimated 

 55,115 sea lions, whereas we estimated 45,917 

 animals in the Eastern Aleutian Islands area, 

 using corresponding estimates from tables 

 5 and 6. Although the individual rookery counts 

 at times differed substantially, the total es- 

 timates made by Kenyon and Rice for the 

 Eastern and Western Aleutian Islands are 

 similar to the estimates made by Fisheries 

 Research Institute personnel. However, with 

 our present insufficient knowledge of seasonal 

 variations within one rookery and between 

 rookeries, as well as between years, any 

 further discussion and comparison of the 

 figures from individual rookeries would need 

 additional observations. 



No photo census exists for rookeries in 

 Southeastern Alaska, but visual estimates 

 were made by Maurice Fields of the Fish and 

 Wildlife Service in the spring of 1957 while 

 he was flying patrol of the halibut fishery 

 with the U.S. Coast Guard (table 11). These 

 estimates, totaling 8,715 animals, correspond 

 to earlier ones given by Brooks (Alaska 

 Fisheries Board and Alaska Department of 

 Fisheries, 1957, p. 52-54). 



13 



