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NORTH AMERICAN FAUNA 68 



all individuals could not be counted in the time available. In such 

 groups we counted a sample of 10 to 50 animals. We then visually- 

 divided the remainder of the group into sectors equivalent to the 

 counted sector to obtain an estimate of the total number of animals. 

 Aerial photographs were taken of unusually large groups to ascer- 

 tain the accuracy of the field estimates (see Aerial Photography). 

 The flight path was divided at the center line of the aircraft. One 

 observer stood behind the pilot and the other behind the copilot. 

 Otters were seen to a distance of at least 1 mile on each side of the 

 aircraft during excellent survey conditions and to at least 1/2 

 under good conditions. 



The width of the survey track was ascertained by flying at survey 

 height over an air strip of known length. In this way each observer 

 obtained a reference point on the wing of the aircraft, which from 

 his position in the aircraft during surveys delimited a known dis- 

 tance on the surface. 



Observation conditions were evaluated during the surveys and 

 were classified as follows : 



Excellent — no wind, high overcast (water glassy and no glare). 



Good — light wind (to 6 or 8 knots) and overcast; or no wind (glassy- 

 water) but sun glare present. 



Fair — light wind to 10 knots and surface glare or wind 8 to 15 knots and 

 sky overcast. 



Poor — winds over 10 knots and glare on water, or wind over 15 knots 

 regardless of sky cover. 



When possible, survey operations were suspended during fair 

 or poor conditions, because too few otters could be seen and the 

 errors in the census could not be properly evaluated. 



Observations were recorded by one of the biologists, or by a 

 third person assisting him. Each observation was immediately 

 plotted on a U.S. Coast and Geodetic Survey chart. 



Several aerial surveys which supplemented the comprehensive 

 surveys were conducted from single engine aircraft and from a 

 Grumman Widgeon. Also, the U.S. Navy cooperated by sending 

 Fish and Wildlife observers on survey flights in a UF-2 Grumman 

 Albatross aircraft. 



Data were gathered in 1959 to provide a factor for computing 

 estimated total sea otter populations from aerial counts. 



In an effort to ascertain as nearly as possible the number of sea 

 otters occupying a particular coastal area at Amchitka Island, 

 inshore and offshore surface surveys were repeatedly conducted 

 by dory. A total of 17 survey counts were made along a 13-mile 

 section of coast from (and including) Crown Reefer Point 



