Shrimp farms, fire or palm oil? Changing causes of proboscis monkey habitat loss

Abstract

Proboscis monkeys, endemic to Borneo, inhabit the fastest-disappearing forest types within the island. Previous studies described multiple causes of their habitat loss, with aquaculture and logging figuring among the major threats. In Balikpapan Bay, which hosts one of the largest populations of the species, a previous Population Viability Analysis identified wildfires as the biggest threat. In this study, we analysed proboscis monkey habitat loss in Balikpapan Bay from 2000 to 2017 by combining satellite images with information on the specific causes of habitat loss available from regular monthly monitoring. We did not identify wildfires and aquaculture as the most prominent causes of recent habitat change. Instead, our data highlighted the recent negative impact caused by the development of industry and infrastructure. Palm oil production caused habitat loss throughout the period, but it advanced from plantations development to the development of the processing industry. The rate of habitat loss is slower compared to all previous estimates, and slowed down even further following increased conservation efforts after 2007. However, it is most detrimental to the non-mangrove habitat, which may provide proboscis monkeys with key food resources. The rate of mangrove loss may therefore be a poor indicator of the future prospects of the population.