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The double-count technique in aerial surveys, a variant of the mark and recapture method, was tested over islands offshore northern Quebec to estimate the number of polar bears that retreated there in the summers of 1986 and 1987. One front observer and two lateral ones surveyed six areas from aboard a twin engine DC-3 aircraft, independently reporting the number of animals they saw to the crew navigator. Bears were classi- fied as being seen both in front and on the side, in front only or on the side only, making it possible to estimate correction factors. Although the observed strip covered 1.75 km on each side of the aircraft, the bear visibility rate exceeded 60% for lateral observers; the low vegetation of the islands and the contrasting colour of bears explain this high visibility. Corrected bear density varied between 0.4 and 14.2 animals100 km-' accord- ing to year and area. The doublecount technique could be used to estimate the size of bear populations retreating on the islands and the coasts of Hudson Bay during the ice-free period, but its costs would have to be evaluated and compared with current techniques before including this method in management programs.

Double Counts in Aerial Surveys to Estimate Polar Bear Numbers During the Ice-Free Period