Composite mark-recapture line transect surveys

Statistical models which unify line transect and mark recapture models for closed heterogeneous populations are presented. The models extend conventio nal line transect models by including a mark recapture component which allo ws relaxation of the conventional assumption that detection on the tracking is certain. They generalize existing mark recapture models by including a statistical model for the distribution of explanatory variables which affec t detectability or catchability, and they allow this distribution to be est imated simultaneously with detection probabilities. In a line transect cont ext, independent observers represent the capture occasions; The issue of un modelled heterogeneity is addressed and composite survey methods are propos ed which allow observable heterogeneity to be modelled while at the same ti me minimising unobserved heterogeneity by design. "Asymmetric" designs, in which the areas searched by the independent observers is separated and one observer sets up trials from which the other platform's detection function is estimated, are proposed. Such designs have substantial advantages over d esigns which treat the two platforms symmetrically. Recaptures/resightings are assumed to occur without error. In practice this is seldom a realistic assumption and the methods presented here could be improved by incorporatin g uncertainty associated with recapture/resighting identification. Neverthe less, the methods provide a flexible framework for estimating animal abunda nce combining line transect and mark recapture methods.