264 NORTH AMERICAN FAUNA 68 



JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC- 25 



30 . 



20 



T 1 1 P 



DEAD OTTERS 



lllllllllllllll: 



OBS, PER. JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. 

 NO. OBS. 4 8 3.5 5 2 3 



Figure 102. — Average seasonal mortality of 311 sea otters found dead on 

 Amchitka beaches 1955-63, and average monthly wind velocities in the 

 outer Aleutian Islands measured by the U. S. Weather Bureau, 1960 

 through 1963. 



or high velocity winds was quite evident. It was also evident, how- 

 ever, that the wind, as such, was only indirectly responsible for 

 precipitating mortality and that more detailed information con- 

 cerning environmental stresses was needed. Therefore in 1962, 

 between 19 January and 31 March (70 days), I kept a daily record 

 of surf conditions and sea otter mortality for both the Bering Sea 

 and Pacific Ocean coasts of Amchitka. Five surf conditions were 

 recorded: calm (no surf), light surf, moderate surf, heavy surf, 

 and violent surf. 



The vast extent and great depth of the Pacific Ocean as com- 

 pared to the relatively small and shallow Bering Sea creates con- 

 ditions responsible for differing surf conditions on the coasts ex- 

 posed respectively to these two bodies of water. 



Under the force of storm winds, heavy seas may build up in the 

 Bering Sea, but within a few hours after the passing of a storm 

 the surf may subside and relatively calm or moderate waves may 

 prevail. 



In contrast, ground swells in the Pacific Ocean may travel to 



