154 



NORTH AMERICAN FAUNA 68 



otters per square mile). By 1943 the population density was high 

 on both north and south sides of the island but nearly equal (43 

 and 41 otters, respectively, per square mile). The difference ob- 

 served in 1949 (10 otters per square mile of habitat on the south 

 side of the island and 19 on the north side) probably resulted from 

 mortality and emigration caused by depletion of food species that 

 must have occurred in earlier years v^hen the population on the 

 south exposure was very dense (42 otters per square mile). By 

 1959 the population reached a condition of relative equilibrium 

 with the population evenly distributed (19 otters per square mile) 

 on both north and south shores of the island (fig. 73). By 1965 

 considerable divergence again occurred, the density on the north 

 side increasing to 25 otters per square mile and on the south side 

 decreasing to 8. Additional detailed studies over a period of years 

 will be necessary to understand the observed population fluctua- 

 tions. It is possible that significant numbers of otters might move 

 across Oglala Pass to Rat Island. 



qI I I I I I I I I I I I I 1 L__J 1 1 1 1 1 1 1 1 1 



1936 1939 1943 1949 1959 



YEAR OF COUNT AND ESTIMATE 



Figure 73. — Changes in population density on the north and south coasts of 

 Amchitka Island, 1936-59. Estimates of the population density are based on 

 field counts (see table 23). 



