The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Assessing the Population of Proboscis Monkeys and Threats to their Survival in Balikpapan Bay, East Kalimatan, Indonesia


1Faculty of Humanities and Social Sciences, Oxford Brookes, 2Faculty of Biology, University of South Bohemia, 3Laboratory of Tropical Forest Research Centre, Universitas Mulawarman

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Few data exist on proboscis monkeys in the mangrove forests of Balikpapan Bay in East Kalimantan, Borneo. In order to ascertain the current population levels of Nasalis larvatus in the bay, a boat survey was undertaken encompassing 15 different rivers over a three month period from May-July 2012. Over 180h of observations were recorded and resulted in an encounter rate of 341 individuals and 57 groups. When compared to a similar study in 2007, this translates to a 30% decrease in proboscis groups over the past five years. The bay was divided into two subpopulations, the north (6.67±4.179) and south (2.43 ± 1.40) (t(11)=2.373 P= 0.56), and this study found there was no significant difference in encounter rates between these subpopulations. Population density was 0.33 groups/km2 and 2 individuals/km2. Spearman’s rank was used to see if there was any relationship between group population and the distance to the nearest industry or settlement (rs=0.1973 N= 15 p= 0.47) and it appears to be negatively correlated. Due to the methods used and lack of further habitat analysis, these data cannot be extrapolated, but this study highlights that Balikpapan Bay still represents one of the largest populations of proboscis monkeys in Kalimantan. It is important that these findings are made available in order to further research in the area and to afford the current population protection against the destructive anthropogenic activities occurring within the bay.

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