Density Estimation by Variable Area Transect

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Abstract
The frequency distribution of the distance from a randomly selected point to the rth nearest organism contained in a variable area transect is described. Estimators of density and variance are derived for both randomly distributed and aggregated populations. For randomly distributed populations exact confidence intervals are available. On an effort-precision criterion the method is more useful than other spatial distribution based density estimators. Under the condition where effort is a linear function of distance covered and numbers of organisms counted, the effort expended in achieving a desired level of precision is the same as that for quadrats; the variance of effort depends on the difficulty in counting and in covering the distance. An example using pismo clams (Tivela stultorum) is given: the density of clams was 1/2.87 m2. The method was superior to that of other distance-measures and quadrats.