The Relationship between Population Density and Body Size of the Giant Mountain Crab Indochinamon bhumibol (Naiyanetr, 2001), an Endangered Species of Freshwater Crab from Northeastern Thailand (Potamoidea: Potamidae)

The giant mountain crab (Indochinamon bhumibol) is endemic to Loei Province in north-eastern Thailand. Although, little knowledge is available on the factors affecting population dynamics and individual fitness. This study aimed to investigate the relationship between the population density and body size of the crab. The mark–recapture method was conducted in Phu Ruea National Park (PR, small area) and Phu Luang Wildlife Sanctuary (PL, large area) between February 2018 and January 2019. The crabs inhabited mountain streams at 400–1100 m. The average water depth and width were 0.6 m and 8.3 m, respectively. In total, 879 individuals were caught from PL compared to 583 individuals from PR. Male were more abundant than female in both areas. Male were also larger and heavier, with a mean weight of 145 g, mean carapace width of 76 mm and mean carapace length of 75.7 mm. The average number of crabs caught was higher in the rainy season (66.3 individuals). The crab population was larger in PL (256.7 individuals), which is bigger in size than PR and is located farther from urban areas. The average crab density in PL and PR were 1.7 and 1.6 crabs/m2, respectively. Population density was significantly correlated with body size parameters: body weight (r2 = 0.066, df = 1196, p < 0.001), carapace width (r2 = 0.053, df = 1196, p < 0.001) and carapace length (r2 = 0.067, df = 1196, p < 0.001). The findings of this study suggest that a large area size and high population density are important to the conservation of the giant mountain crab in mountainous forests.

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