Abstract
Most aerial surveys designed to estimate numbers of caribou (Rangifer tarandus) lack clear objectives, are inaccurate and imprecise, lack application, and often are doubted by the public. Sources of error in surveys are bias (inaccuracy) and sampling error (imprecision) caused largely by sampling units (strips, secrions of strips, quadrats, or photographs) being inappropriate for highly variable group sizes and distributions. Many visual strip surveys of caribou on calving grounds were inaccurate by 136-374%. Photographic surveys of calving caribou are more accurate but usually have coefficients of variation (CV) of 20-40%, whereas a CV of about 15% is required to detect a 50% change in population size between surveys. Extrapolation of such counts to population size produces unacceptable accuracy and precision. Consequently, no conclusions can be made about changes in population numbers between or among surveys because even large natural fluctuations fall within confidence limits. These problems combined with difficulties of managing caribou populations in remote areas of northern Canada indicate that scarce funds may be better allocated to ecological studies.
Highlights
As a member of a caribou management board, I Beverly and Qamanirjuaq herds of caribou
Main sources of error in caribou surveys based on sampling methods are bias and sampling error caused by highly variable group sizes and distributions relative to sampling units
Visual strip surveys of caribou on calving grounds were inaccurate by an average factor of 2.3 relative to photo based estimates, most surveys of caribou are of unknown accuracy
Summary
Objectives and sampling design Survey objectives must be clearly stated and include components of management, accuracy, precision, and trend detection. 97 483 - 805 5 66 173 - 394 5 147 437 - 928 5 135 759 -1204 6 151 501 - 998 6 change of 50% between surveys is detected by most photographic samples of all caribou on calving grounds Detection of a significant change in population size may be delayed many years if several surveys are required to detect a trend. Counts of forest-tundra caribou I favor attempts at total counts of aggregations during July (Valkenburg et al, 1985; Parker, 1972; Heard & Jackson, 1990b; McLean & Russell, 1988; Couturier et al, 1996). Detection of a 10% or 20% difference in population size between surveys is not possible with common survey sampling methods. ' Data from Heard & Jackson, 1990a, b; Williams, 1995; Gunn, this issue
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