Nest site selection factor analysis of Green Sea Turtle（Chelonia mydas）on the island of Wangan, Penghu

• Main Authors: PENG, KUAN-CHIEH, 彭冠傑
• Other Authors: LO, LIU-CHIH
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/34941421258299769834

碩士 === 國立高雄師範大學 === 地理學系 === 104 === Abstract Wangan island is currently the only turtle sanctuary established by the government to protect the spawning habitat of the green sea turtle, thereby providing an important habitat for green turtles to breed. However, the number of female turtles that come ashore to lay eggs have gradually decreased, which acts as a serious warning signal for the conservation of turtles. As such, the breeding habitats’ condition of green sea turtles is of utmost importance, which both directly and indirectly affects the female turtle’s willingness to come ashore to lay eggs. The geological characteristics of beaches that affect the nesting of turtles include the thickness of sand and water levels, which affects air permeability and moisture when hatching. This study uses topographic surveys based on light transmittance through the sandy beach, geographic information systems, satellite image data, and large-scale spatial patterns to analyze important breeding habitats. Through light transmittance, a high density point cloud of 20 cm high beach contour plot that intricately displayed the topography of the beach was attained. The plot simulated the route the spawning female turtles took and rendered the topography as perceived by the turtle when coming ashore to lay eggs in 3D. Furthermore, while performing the GIS (Geographical Information System) spatial overlay analysis, the spatial location of objects and things were established and researched to attain a quantitative description of the spatial conditions. According to the image analysis, the area of Wangan Island is 7.19 square kilometers. There have not been many changes in roads and settlements in the last 20 years. The average area of the beach is 0.204 square kilometers with an SD of 0.023. However, the monsoon and typhoon have changed the shape of Chang Lai Tsai-Bi Wei beach resulting in the accumulation of sand and noticeable seasonal changes. Sections through the sand show that the deposition of each layer of sand is related to the tide line and the wind – waves have more energy that can bring coral debris above the tide line. Investigating the tidal cycles found that groundwater and seawater were connected, thus the area can both supply gas and allow for gas exchange for the turtle hatchlings. The nesting location of the turtles provided by the Agriculture and Fisheries bureau of Penhu County are currently undergoing overlay analysis. 85% (n=42) of female turtles choose to nest in the grass; 10% (n=42) choose to nest on the border between the grass and sand. Hierarchical cluster analysis of the nest location data showed that female turtles choose nesting locations that are beach-specific. In other words, There is a relationship between the nesting location and the surrounding environmental conditions. It is observed that the spatial distribution of the nesting locations exhibit homogeneous spawning hotspots and parameters. Based on the above, the management of sea turtle breeding grounds requires having fully understood the habitat conditions, being able to protect suitable breeding grounds, and thus provide suitable breeding grounds. Keywords: Green sea turtle (Chelonia mydas) , Biogeography , Lidar Measurement , Geographic Information Systems , Satellite Imagery ,Hierarchical Clustering , Habitat Management.