THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 197 



reached a size which heavily utilizes food resources in the available 

 habitat. Significant population dispersal to nev^ habitat is hin- 

 dered by broad expanses of deep water which prevent feeding. 



The Rat Islands (except Buldir Island) population is an ex- 

 ample. Significant emigration of sea otters from this island group 

 appears to be slowed by passes hundreds of fathoms deep and 

 about 50 miles wide on the eastern and western extremities of the 

 group. The average population density was about 14 otters per 

 square mile of available habitat (table 21). When such populations 

 increase and exceed the carrying capacity of the habitat, heavy 

 mortality occurs because substantial emigration does not occur. 



2. Sparse isolated populations 



The recently established Buldir Island colony and the Samalga 

 and Tigalda Islands populations are examples. Many years may 

 elapse before these populations approach maximum size. The 

 Samalga-Umnak population is separated from the nearest An- 

 dreanof population at Seguam by Amukta Pass, 35 miles wide, 

 and by the Islands of Four Mountains, a total distance of 120 

 miles, where no otters are found. The Tigalda Island colony is 

 about 140 miles east of Samalga. Such small colonies grow slowly 

 because they are rarely augmented by immigrants. 



3. Dense local populations adjacent to areas of vacant habitat 



The Andreanof, Sanak, Unimak, and Shumagin Islands, and 

 the Alaska Peninsula areas furnish examples of populations which 

 today are large but may expand into adjacent vacant habitat. 

 During aerial surveys, comparable observations of expanding 

 distribution and increasing abundance of sea otters were obtained 

 in these areas. Such populations expand rapidly because move- 

 ment of part of the population increment to new areas is possible 

 and minimum mortality probably occurs except at densely popu- 

 lated islands after they are left far behind the spearhead of 

 population grovrth. 



4. Sparse local populations adjacent to areas of vacant habitat 



In the Aleutian Islands three local populations of sea otters — at 

 Atka, Amlia, and Seguam Islands — ^are placed in this category. 

 These populations occupy a tiny part of the habitat available to 

 them. They are separated from other populations by many miles 

 but not by geographical barriers. They may be augmented by an 

 influx of otters from the western Andreanofs. Narrow passes be- 

 tween islands of this group are easily crossed. 



