146 



NORTH AMERICAN FAUNA 68 



the field estimates of large concentrations were 12 percent below 

 the number counted on photographs. The 1965 field estimates, 

 made after studying earlier results, however, averaged only about 

 2 percent below the counts from photographs. Relatively few 

 groups as large as 100 animals were seen, therefore no general 

 correction factor is applied to the field count, as this would not 

 materially affect the overall estimate. 



Date 



Location 



Field 

 estimate 



Photo 

 count 



Percent error 

 in field estimate 



6 Apr. 1962 



Kagalaska Str 



150 



157 





10 Apr. 1962 



- Kujulik Bay 



250 



387 





25 Apr. 1965 



L. Tanaga I . 



300 



334 



—11.0"! 



25 Apr. 1965 



Umak I 



275 



274 



+0.4 ^-2. 



25 Apr. 1965 



Box I 



450 



440 



+2.0 J 



Total 





1,425 



1,592 



112. 



1 Average. 



Surface surveys 



Surface surveys were made in limited areas from an outboard 

 motor-driven dory and by observers using binoculars and telescope 

 from shore (Lensink, 1958; Kenyon and Spencer, 1960). 



A review of observations of sea otters from 1933 through 1962 

 in many Alaska areas indicates that observations of numbers of 

 animals made from the surface are generally less useful than 

 aerial observations. When a local otter population is small, surface 

 observers may miss the animals altogether. For example, on aerial 

 surveys in 1959, 1962, and 1965 Spencer and I were able to count 

 8 to 10 otters in the vicinity of Samalga Island and Cape Sagak, 

 Umnak Island. Reports from Aleut hunters at nearby Nikolski 

 Village during the past 10 years indicate that this population, 

 though small, is permanent. In 1961, R. Thomas and in 1963, 

 G. Baines, fur seal research biologists. Bureau of Commercial 

 Fisheries, visited Samalga. They each spent a 24-hour period on 

 or near Samalga and looked specifically for sea otters. Neither 

 saw otters or any indication on beaches that they were present. 



Lensink (1958) counted otters in the Shuyak and Barren Islands 

 in the summer of 1957, first from the surface and then from the 

 air. The surface count was 211 otters. On an aerial survey of the 

 same area he recorded 515 otters, indicating that at least 59 per- 

 cent of the otters in an area may be missed on a surface survey. 

 On the basis of these surveys, a correction factor of 60 percent 

 is applied to certain surface counts that are discussed. 



Area of habitat 



Sea otter feeding habitat was ascertained to consist of waters 



