Proceedings of the 57th Annual Meeting of the ISSS - 2013 HaiPhong, Vietnam, 2013

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Dynamics and viability of the Critically Endangered Cat Ba Langur: A new perspective for conservation actions

Thuc Duy Phan, Ockie J.H Bosch, Nam Cao Nguyen, Tuyen Thanh Le


The golden-headed or Cat Ba Langur (Trachypithecus poliocephalus poliocephalus) is an endemic species of Cat Ba Island in northern Vietnam. It is listed as a critically endangered species in the IUCN red list because of its small, isolated sub-populations and low population numbers. This study was undertaken to understand the trend of population development and the risk of extinction of the species in the future. This will help conservationists to minimize the risk of extinction, and develop better conservation strategies for this species. A number of methods were carried out to examine the conservation status and life history of the langurs. This included conducting in-depth interviews with 21 members of forest protection groups and 20 staff of the Cat Ba National Park, gathering secondary data from reports and other publications dating from 1997 onwards, and conducting field surveys. These information and data were then used to construct a simulation model for the dynamics and viability of the langur population. The study found that 12 groups of the langurs consisting of a total of 50 – 60 individuals with an average group size of 4.67 individuals survived on Cat Ba Island. Disturbed social structure is one of the most significant reasons causing the stable population in the past twelve years, and it is predicted to continue to stabilize in the next 10 years, reaching 86 individuals by 2050. The validation tests have confirmed that the model is sufficient to be used as a tool for policy analysis and decision making for conservationists on the island. The effects of reproducing population on birth rate, and birth rate are two factors which have the most influence on the number of langurs. This clearly implies that an increase in the reproducing population numbers and birth rate would have a significant effect on the growth of langur population in the long-term. Relocation of non-reproductive groups to reproductive units, strict protection and management are important strategies to save this critically endangered species from extinction. 

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