Application of Removal Sampling to Estimate the Density of Ringed Seals (Phoca hispida) in Barrow Strait, Northwest Territories

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Abstract
The density of ringed seals (Phoca hispida) in 2 to 4 km2 study plots was determined using a combination of removal sampling to determine density of seal holes and estimates of hole to seal ratios. A dog survey technique was adapted to removal sampling, where seal holes located under the snow by the dogs during surveys of fixed effort were marked and treated as removals from the population. Computer simulation indicates that estimates of seal hole density are within 10% of the true population size if for each plot there are .gtoreq. 4 searches, sampling intensity is .gtoreq. 0.85, the coefficient of variation of the estimate in .ltoreq. 0.3, and the probability of detecting a seal hole is .gtoreq. 0.35. The quality of survey results was affected by the number of dogs used to survey each plot, plot size, and surface topography. Densities of seal holes varied from 4.8 to 7.9 holes .cntdot. km-2. Eight seals had an average hole to seal ratio of 3.4. Seal densities ranged from 1.4 to 2.3 seals .cntdot. km-2, and may be much higher if pup production is included.