POPULATION ECOLOGY AND REPRODUCTIVE BIOLOGY OF JAGOR’S WATER SNAKE, Enhydris jagorii (Peters, 1863) AT BUNG KA LOH, UTTARADIT PROVINCE, THAILAND

Abstract

Jagor’s water snake, Enhydris jagorii is an endemic species restricted to the Chao Phraya - Ta Chin basin in the central plain of Thailand. Holotype of this freshwater snake was collected from the vicinity of Bangkok and was firstly described by Peters in 1863. Since then, there is no other information regarding this species of snake until Karns, et al. (2010) reported the new area of distribution of this snake in Bung Ka Loh wetland, Uttaradit Province, Thailand. In modern time, the snake has faced a major threat due to habitat loss and human disturbance. A large area of the wetland has been rapidly developed into urban and agricultural areas. Moreover, the population of this snake has been seriously threatened by uncontrolled fishing around the wetland. In order to protect this endemic species, basic information on natural history is certainly needed. This study was conducted at Bung Ka Loh wetland located close to Nan River, Uttaradit Province during October, 2010 to August, 2012. In this study, 6 morphological characters were measured and 3 types of scale rows were counted and calculated from male and female specimens collected from this wetland. The data of sexual dimorphism recorded was the first report of this freshwater homalopsid species. The results indicated that females exhibited larger and heavier than males in term of overall body size and weight, but not tail length. Males showed the significantly longer tail than female at the same size of SVL. Furthermore, morphological measurements were first reported on neonates. Results from the study of both live and dead specimens indicated that this snake is piscivorous, feeding only on fish. The dominant prey belongs to fish in Family Cyprinidae (31.28%). Observed prey items were small in weight, usually less than 10% of snake body mass and multiple prey items were occasionally found inside their stomachs. Significant difference on diet between sexes of this snake was not found. Additional to this, predation on this snake was firstly recorded in this study. The smallest gravid female specimen that was collected from the site during the period of study was 34.0 cm in SVL. Average clutch size and mass were 11 ±9 embryos (1-28 embryos, n=18) and 56.43 ±50.56 grams (3.1-123.0 grams, n=14), respectively. Significant relationships were found between female morphological characteristics (SVL, TL and body mass) and their clutches, being larger females reproduced larger clutch size and clutch mass (p < 0.05). Females possibly has a seasonal reproduction according to the number of gravid females collected during the two periods of rainy season (March to October in 2011 and May to August in 2012). Seasonal reproduction of these female snakes which is related to the rainy season was supported by significant correlations between the number of collected gravid females and physical factors data collected from the wetland (p < 0.05). However, the conservation status, both international and national levels, of this freshwater snake are underestimated. Hence, the proper status and conservation implication of this freshwater snake are proposed in this study.