THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 157 



reduction of 416 animals, or 27 percent. It is interesting to note 

 that during the interval between surveys 637 otters were killed, 

 either by the Alaska Department of Game for their pelts (502 

 in number) or by the Fish and Wildlife Service for research. 

 Apparently reproduction during the 1959-65 period compensated 

 only partially for the natural and artificial mortality that occurred. 

 It may be concluded that either the habitat limited the otter popu- 

 lation below the 1959 level, or the slow rate of reproduction pre- 

 vented compensatory population growth. 



A summary of the probable history of the rise and fall of the 

 Amchitka sea otter population, as deduced from field studies at 

 Amchitka and by analogy with observed rates of growth in other 

 populations, is given below : 



1. The 1911 population of otters, at Amchitka, was about 100 

 animals. 



2. At a rate of growth of about 10 percent per year, this popu- 

 lation increased to about 3,000 animals in 1935. 



3. In the 1935-43 period, the south side of the island was over- 

 populated and otters moved to the north side. The rate of increase 

 decreased because of mortality caused by overuse of food resources. 



4. By 1943 both the north and south shores were crowded by a 

 total population of over 4,000 otters (more than 40 otters per 

 square mile of habitat) and mortality increased. 



5. By 1949 field observations indicated that the population 

 had crashed to less than one-third of its 1940-43 maximum. Mor- 

 tality rather thDn emigration apparently accounted for much of 

 the decline. 



6. Since about 1949 high mortality annually among juveniles 

 and old adults in the late-winter, early-spring season of stress has 

 caused the population to fluctuate within the range of about 1,500 

 and 2,500 animals (exclusive of dependent young). 



Semisopochnoi.-'-AvsLilsMe information indicates that the sea 

 otter was exterminated at Semisopochnoi during the pre-1911 

 period of unregulated exploitation. They were vulnerable to hunters 

 because the island is relatively small, the band of feeding habitat 

 along the shore is narrow, and there are no offshore reefs. 



No mention is made that sea otters were seen there during the 

 1936-38 expeditions by Murie (1959) and his assistants. V. B. 

 Scheffer told me in 1964 that sea otters were not seen when he 

 landed on Semisopochnoi on 4 July 1937. 



Beals (1943), speaking of military pilots who developed much 

 interest in the distribution and abundance of sea otters while 

 stationed on Amchitka, says "These same pilots have made many 



