THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 195 



The 30 miles of deep open water between Amchitka and Semi- 

 sopochnoi Islands was apparently a less effective barrier. No otters 

 had reached Semisopochnoi in 1943 (when the Amchitka population 

 was near maximum size) but by 1959 the population at Semi- 

 sopochnoi was relatively dense (16 otters per square mile). Move- 

 ment to Semisopochnoi of a substantial number of otters, rather 

 than the slow increase of a small breeding nucleus, during this 

 period is indicated. 



The behavioral barrier 



Considerable data show that the reoccupation of vacant habitat 

 is dependent to an important degree on the inherent behavioral 

 characteristics of the sea otter. 



The sea otter does not undertake seasonal migrations. Recovery 

 of marked sea otters at Amchitka revealed that the home range 

 of an individual otter includes only a few miles of coast. Marakov 

 (1965, p. 212) also found that otters in the Komandorski Islands 

 become attached to a particular area. 



Elsewhere (see Amchitka Island) it is shown that otters move 

 into areas of nearby but unoccupied habitat only in response to 

 ''population pressure" after a large local population has developed 

 (table 23). The Amchitka data indicate that the remanent colony 

 which repopulated the island was probably on the Pacific coast 

 and that significant numbers of sea otters did not move to the 

 Bering Sea coast until 1940 or soon thereafter (fig. 73). 



Substantial population movement from densely populated 

 Kanaga to nearby unpopulated Adak and later from Adak to 

 nearby islands east of it did not occur until dense local populations 

 built up. In 1959 the Adak population had reached a density of 

 31 otters per square mile of habitat (table 28) but only one otter 

 was observed at nearby Kagalaska (table 29). It thus appears 

 that otters tend to maintain an established home range until the 

 effects of a dense population force movement. 



Wandering individuals 



Many observations of individual otters at great distances from 

 large local populations are available. That such wanderers even- 

 tually settle permanently in a locality that offers ideal habitat 

 conditions is indicated by the existence of small colonies at great 

 distances from large population centers. The small colonies found 

 in the Near Islands, Buldir, Atka, Amlia, Seguam, and in the 

 Umnak-Samalga and Tigalda Islands areas in the 1950-65 period, 

 are examples. 



