The report on the 5th survey (September 2004) and the estimation hereafter of the hybrid population of Taiwanese macaques in Wakayama Prefecture, Japan

Abstract

(Objectives) The hybridization between Japanese macaques and Taiwanese macaques, which were introduced to Wakayama Prefecture in Central Japan, is a typical example of the genetic disturbance of a native species by an imported species. The Primate Society of Japan has been monitoring this hybrid population since 1999. The prefecture office succeeded in capturing 295 animals between 200-2004 in a population of which the size was only 200 in 1999. Nevertheless many animals survived because of rapid population growth. This report shows the results of the survey of the hybrid population in September 2004 and the estimation of further population growth based on the results of that survey.
(Methods) Count of group number and the tracing of groups through the setting of quadrates. Direct counts of groups by waylaying groups. Extensive survey of the distribution of groups through monitoring.
(Results) The groups split into 4 in 2004 from 2 in 1999. Mouko1 group was 8-ca.30, Mouko2 was 9-30, Okinono1 was ca.30, Okinono2 was 3, and thus, the total number was ca.50-80 in the study area.
(Discussion): the estimation of further population growth and counter measures. The annual growth rate of the population is estimated as 1.14 (Ohsawa etc. 2004). The estimated size of the whole population is estimated as 51, based on the above-mentioned growth rate. The population size shown in the present population census survey is ca.50-80. So, the estimated size is the same as the minimum of the range of the census number. The estimation of the prospective population size is 91 in 2005, more than 300 in 2016 and 565 in 2020, based on a population size of 80 in 2004. The interruption to the capture of this population would result in a complete waste of the efforts in capturing up to the present.