Morphological description and population structure of an obligate arboreal crab (Labuanium politum) at Kampung Tanjong Assam, Spaoh, Sarawak

Akma Iddin, Masini (2016) Morphological description and population structure of an obligate arboreal crab (Labuanium politum) at Kampung Tanjong Assam, Spaoh, Sarawak. [Final Year Project Report] (Unpublished)

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Abstract

Labuanium politum is an obligate arboreal crab that inhabits the nipah palm tree population in the mangrove area. L. politum also locally known as `Geramak Apong'. This crab is nocturnal species. Morphological descriptions and population structure of L. politum were studied on 17 September 2015 at Kampung Tanjong Assam, Spaoh. Meanwhile, the captivity behaviour study was also conducted on 23 March 2016 at Kampung Tanjong Assam, Spoah. These crabs were caught using a special hook. Samplings covered six plots that involved disturbed and undisturbed area. Eleven samples have been kept alive in a plastic container and two samples also kept in an aquarium to observe their behaviour in captivity. This crab exhibited with squarish carapace, same size of chela and reddish brown in colour. The range size of L. politum collected was from 17.53 mm - 35.99 mm for carapace width (CW) and 19.54 mm - 40.10 mm for carapace length (CL). The size of an egg is approximately 330 μm. The population of L. politum were documented higher in undisturbed area compared to disturbed area. The findings indicated that male crabs found were bigger in size class compared to female. The mean of carapace size (CW and CL) of L. politum showed bigger size in undisturbed area compared to disturbed area and the statistical analysis (2 sample independent t-test, p= 0.05) showed significant differences in the mean size of carapace. The findings of the studies also indicated that the size of males dominated the biggest size class which at range class size 38 mm - 41 mm. The sex ratios of L. politum documented mostly were skewed towards female and 20 % of the females were found berried. The overall evaluation based on densities indicates that Kampung Tanjong Assam populations of L. politum declining caused by exploitation from local people. The sex ratio was reported skewed towards female that might related to densities of nipah palm tree and territorial behaviour of male crabs.

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