Prospects of Sustainability of Thomas langur (Presbytis Thomasi) Based on Group Size in Pinus Jantho Natural Reserve, Aceh Besar, Aceh Province

Thomas langur (Presbytis thomasi) is endemic Sumatran primates. Its distribution is limited in Aceh and small areas of North Sumatra. The population of this species is very threatened because its habitats has been disturbed, especially by forest fires. This study aimed to determine the sustainability of the thomas langur in Pinus Jantho Nature Reserve (PJNR). Observations were conducted from December 2017 to September 2018 in rehabilitation and protection block, with an area of ​​184 ha of research sites. The research method used the strip transect sampling and questionnaire. The numbers of observation transects are 23 strips which differ strip lengths. The results shows that there are several various sizes of thomas langur groups. The seven groups consists of from two to seven individuals per group, with a composition of six groups of one male multi female group and all male groups. The total population size with 34 individuals consists of eight adult males, nine adult females, 12 subadult and five infant. The age structure is categorized as stable age structure that evidenced by the age of young Thomas langur, the total numbers of infant and subadult, the same as adult thomas. The sex ratios of adult thomas langur is 1:1,12, and young ages including infant and subadult, with adults 1:1. The sustainability prospect based on indicators of group size and population size does not continue in the PJNR, however it can develop naturally in the PJNR because it has a group composition Keywords: Presbytis thomasi, Population, Nature Reserve. DOI: 10.7176/JNSR/12-8-04 Publication date: April 30th 202