324 



NORTH AMERICAN FAUNA 68 



area, (4) the western Andreanof Islands (including the Delarofs), 

 and (5) the western Rat Islands. 



ESTIMATED YIELD 



If a harvest is taken from any population annually, the kill 

 should probably be limited initially to about 2.5 percent of the 

 total population (both sexes and all ages older than dependent 

 young). 



The total Alaska fur seal population is about 1,200,000 animals, 

 including an annual production of about 350,000 young (Roppel, 

 Johnson, Anas, and Chapman, 1966). The young constitute about 

 30 percent of the population. In the sea otter it was indicated (see 

 Reproduction in the Female) that 2 years normally elapse between 

 births and that the annual mean number of young in the popula- 

 tion is about 14 percent, or approximately one-half that in the 

 fur seal in which 1 year normally elapses between births. It has 

 been found during many years of cropping the fur seal that, on a 

 sustained yield basis, about 5 to 6 percent of the total population 

 may be cropped annually. Under this management system the fur 

 seal herd grew from a population of about 215,000 seals in 1911 

 to about one and a half million in the late 1940's (Kenyon, Scheffer, 

 and Chapman, 1954) and between 1911 and 1963 yielded 2,761,170 

 skins (Roppel and Davey, 1965). 



Thus, until further experience is gained, it may be concluded 

 that about 2i/^ to 3 percent of the total sea otter population may 

 be cropped annually on a sustained yield basis. 



Further studies of reproduction and of the effect of cropping 

 on populations may modify this preliminary estimate. In spite of 

 the indication that a female sea otter may bear no more than one 

 young in each 2-year interval, it is possible that because maternal 

 care is intensive and prolonged the survival rate of young in a 

 sea otter population might exceed that in the fur seal population. 



CLOSED AREAS 



Many observations indicate that before sea otters move from 

 a populated area to adjacent vacant habitat, a large local population 

 is formed (see Distribution and Numbers). They apparently move 

 as a result of overutilization of food resources by a crowded 

 population. It follows that if vacant habitat is to be repopulated, 

 large local populations should be allowed to form to create the 

 ^'population pressure" necessary to cause significant emigration. 

 Thus, it is my opinion that the ''spearhead" of population expan- 



