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Son Tra Survey Counted 1,487 Rhesus Macaques; Models Put Carrying Capacity at About 1,900

Male and female rhesus macaques in Son Tra Nature Reserve, Vietnam
Conservation · Population & status

Transect surveys on Son Tra Peninsula in Da Nang, Vietnam, recorded 86 troops of rhesus macaques (Macaca mulatta) containing 1,487 individuals. The researchers surveyed about 850 km of transects over 85 days during April, July and August 2024 and again in December 2024 and January 2025, recording group size and age–sex structure.

A transect is a predefined line or route used to survey an area systematically, with observations, signs or sampling points recorded along it.

The 13 troops living near residential and tourist areas differed from the other 73 groups. They had roughly five adult females per adult male, compared with a little over two females per male in the remaining troops. They also contained proportionally more non-adults than the other groups. The authors interpret this as evidence of more breeding females and a larger proportion of young macaques near people and tourist areas.

The population model put carrying capacity near 1,900

The observed demographic data were entered into Vortex, a population-viability model, together with published life-history information. Under the baseline scenario, the simulated population rose from about 1,500 and stabilised around 1,900 individuals, which the authors interpret as an approximate carrying-capacity level under the model assumptions.

The model changed sharply once annual removals reached about 10% of the population: losses began to match or exceed recruitment and the simulated population declined rapidly. At 20% annual removal or more, extinction within 100 years became very likely. The study treats illegal snaring, traffic mortality and permanent relocation following conflict as forms of removal and recommends keeping human-caused losses as low as possible, ideally below 5% annually.

Sources and image credit

  1. Nguyen, V. T., Nguyen, T. A., Nguyen, D. D., & Nguyen, V. L. (2026). Predicting the population trend of the rhesus macaque (Macaca mulatta) at Son Tra Peninsula, Da Nang City. HNUE Journal of Science: Natural Sciences, 71(1), 88–98. https://doi.org/10.18173/2354-1059.2026-0008Primary research article published 20 March 2026. Transect surveys recorded 86 rhesus macaque troops and 1,487 individuals on Son Tra Peninsula. Vortex simulations converged near an approximate carrying-capacity level of 1,922 individuals under the baseline assumptions. Sensitivity analyses placed the transition to rapid decline around 10–12% annual removal; modeled survival probability fell below 50% at 15% annual removal and extinction became highly likely at 20% or more.

Image: Charles J. Sharp — male and female rhesus macaques (Macaca mulatta) in Son Tra Nature Reserve, Vietnam, 27 February 2025; Wikimedia Commons; cropped to 16:9 for Wildlife Vagabond; directly relevant Son Tra location image, not animals individually identified in the 2026 survey · CC BY-SA 4.0 · Source

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