THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 151 



otters at Buldir. The present breeding population probably became 

 established there in recent years. This fact is important because 

 the sea otters must have crossed 55 miles of open water to reach 

 Buldir from Kiska. Buldir reef, a 20-mile strip of relatively shallow- 

 water, extends 20 miles west of Kiska to 15 miles east of Buldir. 

 It offers depths of less than 30 fathoms where food might be found 

 en route, and otters were seen in this area on 27 May 1959 (A. C. 

 Hartt, letter, 1960). 



The observed absence of sea otters at Buldir after intensive 

 exploitation ended in 1911, and their reappearance there in 1962, 

 furnishes another example that, given time, sea otters will find 

 their way from one island group to another across broad expanses 

 of deep open water. 



Rat Island. — The available observations of numbers of sea otters 

 at Rat Island are listed in table 22. These data indicate that popu- 

 lation changes at Rat Island followed a pattern similar to the 

 changes observed at Amchitka during the same period and in 

 more recent years in the Andreanof Islands. No observations are 

 available from Rat Island to indicate that population reduction 

 there was caused by mortality. Presumably, though, as was ob- 

 served at Amchitka, mortality at Rat Island caused population 

 reduction from a high of 31 otters per square mile of habitat to 

 12 to 15 per square mile in recent years. 



Amchitka Island. — A number of surface and aerial counts and 

 estimates of the Amchitka sea otter population have been made 

 since 1935. Estimates of the total population, because of the variety 

 of methods used in obtaining the basic field data, are approxima- 

 tions and are given to represent an order of magnitude. That these 

 approximations are within reasonable limits is indicated by the 

 fact that they reveal a history of population grov^th, decline, and 

 stabilization (with annual fluctuations) that is typical of animals 

 when a "seed population" is given complete protection in ideal 

 vacant habitat. 



The first observation of significant recovery of a sea otter popu- 



Table 22. — Rat Island sea otter population density in SO square miles of 



feeding habitat 



Estimate Otters per Authority and 



Year Count of total square mile survey method i 



1943 705 2 940 31 F. Beals and G. T. Joynt, aerial 



count-estimate. 



1949 234 312 10 R. D. Jones, aerial survey. 



1959 270 360 12 Spencer-Kenyon, aerial survey. 



1965 326 435 15 Spencer-Kenyon, aerial survey. 



1 All unpublished reports in U.S. Fish and Wildlife Service files. 



2 Estimate based on the assumption that 75 percent of the otters were recorded. 



