THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 199 



8. The sea otter is limited to a relatively narrow band of 

 water around islands and along mainland shores where water 

 depths do not exceed 30 fathoms. Under the prevailing weather 

 conditions when aerial surveys were made, sea otters were easily 

 observed. We concluded that in most areas about 75 percent of the 

 sea otters present were recorded. Comparative surface and aerial 

 surveys indicated that about 60 percent of the otters seen on 

 an aerial survey may be missed on a surface survey. 



9. Data obtained on aerial surveys in the Andreanof Islands 

 in 1959, 1962, and 1965 indicated that in this area, having much 

 available and unpopulated habitat, the population is growing at 

 an exponential rate of between 4 and 5 percent per year. 



10. Aerial surveys and other studies conducted between 1954 

 and 1965 in Alaska reveal that large areas of sea otter habitat 

 are not yet repopulated. In certain areas repopulation of vacant 

 habitat is proceeding rapidly (the Andreanof Islands). In isolated 

 areas the habitat may be heavily utilized by a dense population 

 (the Rat Islands). 



11. In all observed areas where estimated sea otter populations 

 reached 20 to 40 otters per square mile of habitat, the populations 

 decreased to about 8 to 15 otters per square mile of habitat. The 

 decrease occurred through mortality (e. g., Amchitka Island) or 

 emigration (e. g., Kanaga and Adak). In years following a popu- 

 lation "crash" the populations at islands may fluctuate between 

 about 10 and 20 otters per square mile of habitat. 



12. Reoccupation of available sea otter habitat is hindered by 

 wide, deep passes between islands. Sea otters readily cross passes 

 about 10 miles wide. Significant numbers may cross 30 miles of 

 open water (e. g., Amchitka to Semisopochnoi). Passes 50 miles 

 or more in width may be crossed by a few individual otters that 

 wander great distances from densely populated areas (e. g., from 

 Kiska to Buldir and from there to the Near Islands). These indi- 

 viduals may eventually concentrate in locations having unusually 

 desirable habitat. 



13. The most significant factor that limits the spread of sea 

 otter populations is the tendency of individual otters to occupy 

 a limited home range. Feeding habitat on one side of an island, or 

 at an island near another having vacant habitat, may become 

 densely populated (to about 40 otters per square mile of habitat) 

 before a significant number of otters move into adjacent vacant 

 habitat even at the home island. Where repopulation was observed, 

 the south sides of islands were repopulated prior to the north ex- 

 posures (e. g., Amchitka, Atka, and Amlia). 



