With estimates of fewer than 1000 mature individuals in the wild, the critically endangered Siamese crocodile, Crocodylus siamensis Schneider, 1801, is one of the least known and at the same time most threatened crocodilian species in the world. Populations have already been depleted to approximately 20% of their former size with habitat destruction, alterations, and loss being the main drivers of population declines. Habitat suitability models were computed using a combination of bioclimatic and remote sensing variables as environmental predictors to evaluate habitat suitability and coverage by designated protected areas across the species’ distributional range. In addition, population connectivity as well as current and future habitat fragmentation through dam construction was assessed by performing population connectivity models. Habitat suitability models show the spatial extent of suitable habitat to be high (46%), although only a small proportion is covered by designated reserves (11%). Population connectivity models showed remnant populations to be highly fragmented. Considering habitat suitability, coverage of reserves and population connectivity the lower Mekong River Basin stretching from the Xe Champhon and Xe Xangxoy rivers in Lao PDR to the Srepok and Sekong rivers in eastern Cambodia seem to be particularly important for future conservation prioritization for C. siamensis. The presently established protected area network is unsatisfactory in terms of size and population connectivity and needs to be significantly improved to successfully sustain viable populations of the critically endangered Siamese crocodile in the future. Copyright © 2014 John Wiley & Sons, Ltd.

ABSTRACT1. The Sunda gharial Tomistoma schlegelii is, with 2500-3000 remaining specimens, one of the least studied and at the same time most endangered crocodile species. Inhabiting peat swamps in Southeast Asia, threats affecting the species are mainly associated with habitat loss and illegal hunting.2. The effectiveness of the existing reserve network in Southeast Asia for the protection of the Sunda garial was assessed by combining spatially explicit habitat analyses derived from land cover information with species distribution modelling. Subsequently, possible improvements of the existing reserve network are derived from the habitat availability analyses.3. The results of the spatially explicit analyses indicate that suitable habitats for the Sunda gharial in Southeast Asia, i.e. peat swamps and riverine forests, are highly fragmented. Spatial coverage of remaining habitats with protected areas fulfilling IUCN standards generally varies among regions and is best in Indonesia. However, large, currently unprotected suitable areas remain in Sumatra. Establishment of 10 additional, already proposed reserves may improve the protection of major parts of the remaining suitable habitats of the Sunda gharial.4. According to the results of this study, the reserve network protecting this species could be significantly improved by expanding it to include seven national reserves not currently listed by the IUCN and an additional 10 reserves that have recently been proposed. Improvements and extensions of the existing reserve networks in Southeast Asia are pivotal to guarantee the long-term survival of the Sunda gharial.