196 



NORTH AMERICAN FAUNA 68 



It thus appears that vacant sea otter habitat is repopulated by 

 two means: (1) Movement of large numbers of otters from a 

 densely populated area to adjacent unpopulated habitat, and (2) 

 wandering individuals that accumulate to form colonies where 

 habitat conditions are ideal many miles distant from dense popu- 

 lations. 



Because of the indicated 4 percent per year rate of growth of 

 the Andreanof sea otter population, the repopulation of vacant 

 habitat at the periphery of a densely populated area, is, today, 

 the most important means by which the sea otter is reoccupying 

 the places from which it was exterminated during the 18th and 

 19th centuries. 



Dispersal of sea otters and population density 



Most animals included in tagging studies at Amchitka were 

 adults when marked and the recoveries indicated that they re- 

 mained permanently along a limited area of coast (see Home 

 Range). By analogy with other species it would seem probable 

 that wanderers, contributing to range extension, might be com- 

 posed mostly of subadult animals. That this may be true also of 

 sea otters is indicated by our failure to observe as many mothers 

 accompanied by small young in newly populated areas as in other 

 areas. In 1959, we saw no otters in Kagalaska Strait, but in 1962 

 we observed 348 there. Aerial photographs of a group of 157 

 animals and another of 59 revealed not one small pup among 

 them. In mid-November of 1965, when this area was well behind 

 the vanguard of population expansion, I spent 2 days in Kagalaska 

 Strait and saw a number of mothers accompanied by young. 



Two possible conclusions concerning the otters which first ap- 

 peared in Kagalaska Strait are indicated: (1) All were males, and 

 (2) they were mostly subadults of both sexes and had not born 

 young. 



Estimates of population density, or the number of sea otters per 

 square mile of available habitat, were obtained in several Aleutian 

 areas. Among these were locations where substantial populations 

 have existed for many years, and also recently repopulated areas. 



On the basis of geographical barriers and population density, 

 sea otter populations in Alaska may be classified according to four 

 general categories (two densities of isolated populations and two 

 densities of populations adjacent to available habitat). 



1. Dense isolated populations 



This category includes populations of sea otters that have 



