Gibbon population status and long-term viability: Implication for a newly established protected area management

Effective protected area management is a crucial process for biodiversity conservation, and its
effectiveness can be evaluated using the status of indicator species. Monitoring changes over time
in the status of indicator species is an essential tool for designing and improving management
plans for protected areas. Due to the preference for pristine habitat hoolock gibbon can be
considered indicator species for habitat quality. We therefore defined changes in the status of the
eastern hoolock gibbon (Hoolock leuconedys) over 16 years (2005–2021) by estimating density
changes and population viability in Mahamyaing Wildlife Sanctuary (MWS), a newly established
protected area in western Myanmar. Using the acoustic point count method, we estimated the
gibbon density to determine the impacts of selective logging and human disturbances on this
species. This survey was conducted between February and March 2021 at 22 sampling sites,
covering 352 km2 of evergreen and mixed deciduous forests in Mahamyaing Wildlife Sanctuary.
We used distance sampling method to estimate an overall gibbon density of 0.97 groups/km2,
which appeared to be dramatically lower than a previous estimate of 1.81 groups/km2 from 2005,
defined using the same method. We then divided the Sanctuary into three zones and defined the
minimum viable population (MVP) for gibbons in each zone to support management policies for
the long-term persistence of the species. Moreover, the population viability analysis indicated that
the population of eastern hoolock gibbons in the entire study area was seriously declining to
lower than 1000 gibbons by the year 2055. By our estimation, around 4400 groups are needed for
the long-term persistence of gibbons in Mahamyaing Wildlife Sanctuary. Our results highlight the
detrimental effects of selective logging and human disturbance on gibbons, and presumably
wildlife in general, in Mahamyaing Wildlife Sanctuary and the problems of inadequate protection
level and management, underscoring the need to address these threats through targeted conservation
efforts.