Estimating Bias in Aerial Surveys of Harp Seal Pup Production

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Abstract
We present methods for reducing bias in aerial surveys caused by counting errors and changing availability of members of the population to be photographed. Data are from an aerial survey of harp seal (Phoca groenlandica) pups off southeastern Labrador [USA] in March 1983. The estimated correction for pups that had not been born or had temporarily left the ice at the time of the survey was 3%; however, surveys conducted before 10 March or after 20 March will underestimate production. Errors in analyzing photographs of pups caused the number of pups to be underestimated by about 10%. We conclude that failure to detect all whelping concentrations is likely to be the largest source of error in future surveys.

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