250 



NORTH AMERICAN FAUNA 68 



Natural Mortality 



Data are not available to indicate exactly when the regular 

 annual occurrence of considerable late-winter, early-spring mor- 

 tality among sea otters on Amchitka Island began. Natives who 

 trapped foxes there in 1938-39 reported that "many" dead sea 

 otters were found on beaches in that winter. Between 10 July 1939 

 and 15 January 1940, however, a careful search revealed only six 

 skeletons on beaches (Loy, 1940). Sea otter wardens J. B. Mangan 

 and G. Ritter, who were on Amchitka from 1 February to 5 Sep- 

 tember 1940, reported salvaging only **two sea otter skins and 

 skeletons** (Amchitka Island Report, September 5, 1940, U.S. 

 Fish and Wildlife Service files, unpublished). 



During the years that Amchitka was occupied by military 

 forces, 1941-47, no reports of unusual sea otter mortality were 

 made. V. B. Scheffer and I visited Amchitka on 12 November 1947 

 and recorded (field notes) that in walking about 4 miles of beach 

 we found the remains of six sea otters. At the time we attributed 

 these deaths to military personnel occupying the island, two of 

 whom we saw target practicing along the beach. Only a fraction 

 of the beaches where dead sea otters were found in subsequent 

 years was examined. 



In the light of later experience on Amchitka, I am inclined to 

 believe, on the basis of what I saw on that one day in 1947, that 

 considerable natural mortality occurred in the winter-spring 

 period of 1946-47. In the late-winter, early-spring period of 1948, 

 Elmer Hanson, a civilian employed by the Army on Amchitka, 

 estimated that more than 100 otters died on Amchitka beaches. 

 Jones and Hanson recorded 124 dead otters on the beaches in the 

 late-winter, early-spring period of 1949 (Jones, R. D., narrative 

 reports of 1 January to 30 April and 1 July to 30 August 1949, 

 unpublished). Both Jones and Hanson spent much time on Am- 

 chitka during or after World War II. Neither remembers observ- 

 ing a significant number of dead otters on beaches before 1948. 

 Thus, it appears that an annual late-winter, early-spring "die-off" 

 began in the late 1940*s. All available counts and estimates are 

 shown in figure 95. An analysis of observed mortality from 1955 

 to 1963 at Amchitka is presented in the following pages. 



Studies conducted 1955—63 



During the 1955-63 study period, I repeatedly surveyed the 

 same beaches that were searched for dead otters by previous ob- 

 servers. The majority of moribund otters haul out above the high 



