Historical Perspective, Distribution, Ecology and Population Genetics of Saltwater Crocodile (Crocodylus porosus Schneider, 1801) in Sarawak, Malaysian Borneo

This study is designed to gather information on historical exploitation and ongoing HCC; recent distribution and ecology of crocodile and genetic relationship of crocodile population in Sarawak, to aid sustainable crocodile management and finding solutions for mitigating the HCC. Historical data saw a connection between the exploitation of crocodile with decreasing trend of HCC in Sarawak from the Rajah Brooke era (1900 – 1941) until the post-war period (1946 – 1979), and an increasing trend of HCC from 1980 until 2017 in response to the recovery of the animal populations. Since 1900, crocodile attacks had been occurred in 22 major river basins (RB) in Sarawak, suggesting that the reptile has been widely dispersed throughout all major river basins in the state. For 118 years (1900 – 2017), the highest number of crocodile attacks were recorded in Lupar RB (22.2%) and the attacks had happened up to the inland areas of Belaga and Pelagus in Rajang RB. Further analysis of incidents show crocodile attacks were associated with the human activities pattern, where more attacks involved male victims (84.4%) and adults from age 31 to 40 years old (19.3%). The data also revealed that crocodile attacks in Sarawak could happen anytime regardless of the time, month, season, lunar cycle or tidal. However, more attacks were recorded during the daylight, in the months of March and April, during the Northeast monsoon, at the nights of the first quarter of the lunar cycle and at the time of high tide. Furthermore, fishing (25.2%) and bathing (24.4%) possess the highest risk of crocodile attack in Sarawak, clearly showed that crocodiles are more likely to attack when the victim is in water. Crocodile survey in selected tributaries in Rajang RB showed the distribution of the reptiles throughout the river basin with higher crocodile density at the lower region, the highest density was in Igan River (1.37 individuals/km); while in the middle and upper regions had recorded relatively low density with the lowest density recorded was in Katibas River (0.06 individuals/km) and no crocodile was spotted in Kanowit River. Four out of eight surveyed rivers in Rajang RB recorded increase in the density of crocodile compare to previous survey suggesting that the crocodile population in the river basin is experiencing recovery. The presence of crocodile in different regions (lower, middle and upper) of Rajang RB indicated that C. porosus in Sarawak live in wide range of habitats; from large salt water river system and small tidal tributaries (near to estuary) in lower region into hypo-saline or fresh water non-tidal tributaries in the middle and upper regions. Variation in term of density and distribution of crocodile between the different regions are mainly influenced by the saline characteristic of the river, habitats and the abundance of food sources for crocodile. Based on the analysis of DNA microsatellite sequence data, distinctive subpopulations of C. porosus according to geographical area (river basin) could be observed. High gene flow (Nm) among the crocodile subpopulations suggests frequent movements of the reptile happen across the river basins throughout Sarawak. In general, populations of C. porosus in Sarawak are experiencing expansion as supported by the mismatch distribution and evolutionary neutrality test data, suggesting that populations of crocodile in Sarawak are panmictic population. The findings of the present study imply that increasing of crocodile attacks is associated with the recovery and increased distribution of the reptile in Sarawak, thus crocodile management should emphasis on mitigating HCC and simultaneously continue the efforts for conservation of crocodile and its habitat.
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\nKeywords: Crocodylus porosus, human-crocodile conflict, recovery, expansion.

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