THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 191 

 DISCUSSION 



In the foregoing section, observations of sea otter populations 

 obtained between 1935 and 1965 in several geographic areas were 

 reviewed. The data included aerial and surface counts, total 

 population estimates based on them, measurements of available 

 habitat, and population densities in different areas. The field 

 observations and the conclusions derived from them are discussed 

 below. 



Rate of population increase 



Two methods may be used to ascertain the approximate rate of 

 increase in a sea otter population: (1) The annual rate of repro- 

 duction and mortality in a population may be studied ; or (2) otters 

 in an isolated population may be counted at intervals and the 

 increment found directly. The first method is treated elsewhere. 

 The results obtained by the second method are discussed below. 



Because movements of large numbers of otters from one island 

 to another were recorded, it was evident that the area included 

 in population surveys must be sufficiently large to include locations 

 where both emigration and immigration occurred. The population 

 surveys in the Andreanof Islands furnish the best available in- 

 formation on which to base a study of population grovrth. On the 

 east, this otter population is isolated from the small population of 

 the Umnak-Samalga Islands by 120 miles, which includes Amukta 

 Pass and the unpopulated Islands of Four Mountains. On the west, 

 the study area is separated from the Delarof Islands by 14-mile- 

 wide Tanaga Pass. 



This sample area, about 210 miles in length, includes densely 

 populated islands adjacent to others having unoccupied habitat. 

 Aerial surveys of the Andreanofs in 1959, 1962, and 1965 were 

 conducted under comparable conditions by the same observers. 

 The small, semi-isolated populations at Atka and Amlia at the 

 eastern end of the sample area showed a larger rate of increase 

 than did the total Andreanof population. Probably these colonies 

 were augmented by wandering individuals that formed the van- 

 guard of the massive eastward moving population of the Kanaga- 

 Adak-Kagalaska Islands segment of the sample area. 



The rate of the Andreanof population increase of about 12-1- 

 percent in each of two 3-year periods or over 4 percent per year, 

 is less than the rate of increase postulated by Soviet biologists. 

 The rate of increase was at first presumed to be 10 to 12 percent 

 per year by Barabash-Nikiforov (1947) but he finally concluded 

 that this rate was not in accord with his field observations and 



