The comparison of Design -based and Model -based approaches for precision and robustness of abundance estimation by simulation studies from Line transect data.

Speaker: Yasutoki Shibata (The Graduate School of Environmental and Information Science, Yokohama National University,Japan)

Abstract

“Design -based and Model -based approaches are used for abundance estimation of cetaceans. To compare performance between both approaches, many simulation studies are reported from with synthetic data. It is useful to know the precision and robustness of both approaches so that an informed choice can be made under plausible survey and distribution conditions. Under a gradient distribution assumption (which is standard in this area), a line transect survey is carried out, but crucially including estimates of robustness and precision… Parameters and covariates that are needed for generating a virtual space and whales were based on Japanese whale research programs under a special permit in the Antarctic. A virtual survey was carried out under a framework of stratified systematic sampling of a line transect survey. It was assumed that g(0)=1, and all animals within a fixed width are detected. Abundance estimation from GLM, GAM and line transect methods were carried out and their precision (CV: Coefficient of Variation) and robustness (RMSE: Root Mean Square Error) were compared under 144 scenarios. GLM showed better performance than for CV in almost all scenarios, whereas line transect method performed better in terms of RMSE. The CVs and RMSEs were analyzed using a random effects model ANOVA.

 The result of the ANOVA indicated an interaction term between the true

distribution of whales and the pattern of stratification. This term

always represented more than 10% of the total variance for each CV and

RMSE from both the GLM and the line transect method.”