266 



NORTH AMERICAN FAUNA 68 



exceeded on both coasts. Thus, mortality occurred in proportion 

 to the available habitat and population size rather than in pro- 

 portion to the intensity of storm wave activity. About two-thirds of 

 the available habitat, population, and mortality were found on the 

 Pacific coast (table 59). 



Although the period of heavy surf began in late January, the 

 increasing rate of sea otter mortality did not reach a peak until 

 the end of February (figs. 103 and 104). This is explained by the 

 fact that the otters enter the winter with reserves of body fat and 

 in good general physical condition. During weeks of stormy 

 weather, those animals least able to supply their nutritional needs 

 exhaust their physical reserve. After becoming emaciated and 

 being subjected to continuing environmental stress, they die. 

 Autopsies reveal that almost all animals found dead on beaches 

 show signs of starvation in spite of the fact that their intestinal 

 tract often contained the remains of sea urchins (see Food and 

 Feeding Behavior). 



Annual mortality at Amchitka estimated from animals found dead 

 on beaches 



Since many of the hauling-out areas on the eastern half of 

 Amchitka were searched carefully and frequently during the 

 period of high mortality, probably most of the dead otters in 

 these limited areas were found. The habitually used hauling 

 grounds constitute less than 10 percent of the shoreline on the 

 eastern half of Amchitka. Other areas could not be searched as 

 carefully as the areas of concentration. On several occasions, dead 

 otters that had been buried in kelp by storm waves or carried from 

 the beach area by eagles were found after having been missed on a 

 previous search. A few dead otters were found well up on off- 

 shore rocks that we rarely visited. On the basis of these and other 

 field observations, I have estimated that at least 30 percent of the 



Table 59. — Sea otter mortality in relation to population counts and available 

 habitat, eastern half of Amchitka 







Pacific coast 



Bering Sea coast 







Number 



Percent 



Number 



Percent 



Dead otters i 



otter population ^ 



Available habitat ^ — 





70 



766 



45 



66 

 71 

 67 



36 

 310 

 22 



34 

 29 

 33 



1 Count, 19 January to 4 April 1962. 



2 Aerial count, 19 May 1959. 



3 Square miles of water 30 fathoms or less in depth, eastern half of Amchitka. Measured from 

 U.S. Coast and Geodetic Survey Chart 8864. 



d 



