Parametric Models for Line‐Transect Estimators of Abundance

Abstract

The estimation of the abundance of animal populations with the line—transect sampling method requires that a sighting model be postulated to represent the decreased probability of a sighting as its distance from the transect line increases. The development of parametric sighting models and estimation techniques is reviewed, and general procedures for variance estimation are given. Two new models and their corresponding abundance estimators are developed. The half—normal model provides a useful alternative to the widely used exponential model. The generalized exponential model contains the half—normal and exponential models as special cases and has the flexibility to account for a wide range of sighting phenomena. The new models are applied to transect surveys of porpoise schools and the results are related to sampling and ecological conditions. Criteria for model selection and transect design are discussed.