Bayesian estimation of population size in raccoon (Procyon lotor) using state-space model based on removal sampling

Abstract

Raccoon population size (Procyon lotor) and the conversion factor from CPUE to raccoon density were estimated using Bayesian removal sampling methods based on a state-space model with capture records from a high density area in Chiba prefecture, Japan. Raccoons had been captured via pest control in the Shiota River basin (35.1 km²) in Isumi City, Chiba prefecture, from June 22, 2012 to March 23, 2013 with 100 cage traps (mean nearest distance was 301 m). Fifty three adult males, 29 adult females and 55 juveniles (total 137 raccoons) were captured via pest control. The population size of each age-sex class was estimated as 89 adult males, 103 adult females and 130 juveniles (total 322 raccoons). Although more than 76% of adult females and juveniles could be removed using 100 cage traps in the first three months of the pest control, the density of adult males was maintained throughout the whole control period. We suggest that unchanged density of male raccoons can be maintained by the dispersal of young male raccoons from their natal areas, and of nomadic adult male raccoons from adjacent areas.