屋久島におけるアカウミガメ孵化幼体の脱出に与える踏圧の影響

抄録

The emergence success rates of loggerhead turtle hatchlings on Inakahama beach, Yakushima Island, Japan are decreasing. This phenomenon seems to be related to human interference on the beach. In order to investigate this relationship, locations and numbers of loggerhead turtle nests were recorded as well as the numbers of visitors to the beach. Furthermore, pressure, temperature, and CO₂ concentrations were measured in the nests and some were excavated to check the developmental stage of the embryos. Mean emergence success rates in nests located in “high traffic” areas proved lower than those in more remote areas. In addition, these rates were negatively correlated with accumulated pressure from trampling during the period from nesting to emergence. This suggests that the trampling of nests by visitors negatively affects the emergence of turtle hatchlings and our results show that trampling of a nest by more than 650 people could lead to a 50% reduction of hatchlings, and that more than 1200 people could lead to the complete mortality of the hatchlings of the nest. Lowered heat conductivity of their nests due to visitor’s trampling effect led to overheating of the nests because of their metabolic heat production and resulted in a retardation of hatchling emergence. Therefore, it is proposed that beach visitors should be prohibited from entering the conserved loggerhead nesting area during the nesting season in order to ensure a high emergence rate of hatchlings from their nests.