140 



NORTH AMERICAN FAUNA 68 



Table 19. — Summary of sea otters observed and estimated in Alaska 



[See tables in sections for counts by islands. Most areas have now been surveyed several times. 

 The highest counts which were made under optimum conditions were selected for this sum- 

 mary. Three observers, D. L. Spencer, C. J. Lensink, and K. W. Kenyon gathered most of 

 these data] 



Aerial surveys 









Estimated 



Estimated 







Otters 



total 



total 



Area 



Year 



observed 



otters 1 



1965 2 



Near Islands 



1965 



27 



45 



45 



Rat Islands 



1965 



3 3,147 



4,196 



4,196 



Delarof Island.— 



1965 



3 653 



871 



871 



Andreanof Island 



1965 



3 5,805 



7,760 



7,760 



Islands of the Four Mountains 



1965 



0 



0 



0 



Fox Islands 



1965 



2.935 



3,913 



3.913 



Bogoslof Island ._ 



1962 



0 



0 



0 



Sandman Reefs 



1962 



638 



879 



1,017 



Sanak Island area . 



1962 



548 



746 



863 



Shumagin Islands 



1957 



1,829 



2,724 



3,153 



Pavlov Islands 



1962 



4 



8 



12 



Alaska Peninsula 



1962 



949 



1,317 



1,383 



Semidi Islands ... . 



1957 



5 



10 



12 



Kodiak area 



1957-59 



722 



973 



1,237 



Prince William Sound 











and Kayak Island— 



1959 



702 



1,004 



1,004 



Total 





17,964 



24,446 



25,466 



1 See Aerial Surveys for method of estimating. 



2 Projected in the regions where growth was observed on the assumption that the increase is 

 at the rate of 5 percent per vear. 



3 Total 9,605. 



now available indicate that in significant areas sea otter popula- 

 tions have declined and are less than the estimates which Lensink 

 computed on the basis of figures then available to him. Lensink 

 (1960) considered that sea otter feeding habitat included waters 

 to a depth of 50 fathoms, but no evidence is available that they 

 descend to this depth (see Diving). Because of this assumption a 

 greater area of available habitat and greater population potential 

 was postulated by Lensink than is indicated by information now 

 available. Also, Lensink's (1960) estimates for a large sea otter 

 population at Amchitka do not agree with the modern or historical 

 data for this area. The rate of population growth which he postu- 

 lated is greater than indicated by the data now available. In addi- 

 tion, as shown later, the Amchitka population ''crashed" in the 

 1940's and now fluctuates annually near a population about one- 

 half its maximum size. 



Aerial surveys 



The most extensive aerial surveys consumed about 200 hours of 

 flight time in a DC-3 aircraft (table 20) . Air speed was maintained 

 at 120 knots and flight altitude varied from 200 to 400 feet, de- 

 pending on winds and nearby terrain. Two observers counted 

 otters from the aircraft's cockpit. Some groups were so large that 



