Factors Affecting the Long-Term Population Dynamics of Green Turtles (Chelonia mydas) in Ogasawara, Japan: Influence of Natural and Artificial Production of Hatchlings and Harvest Pressure

Abstract

Abstract The Ogasawara Islands in Japan represent an important rookery for green sea turtles (Chelonia mydas) in the Pacific Ocean. The marine turtle population in these islands was severely depleted due to overexploitation in the 1800s; however, continuous nesting surveys starting in 1975 showed signs of a gradual recovery, and an upward trend of nesting females has been observed in recent years. The Japanese government undertook a “hatch and release project” to recover the turtle stock in 1910 as the world's first attempt of a sea turtle hatchery. A total of more than 251,000 hatchlings were released into the wild as a part of the project; however, its contribution to the recent increase in nesting females is not well understood. The increase in nesting females may be attributed to the temporary suspension of the turtle harvest and reduction of catch from 1942 to 1968, which allowed for stable production of hatchlings from natural beaches. This study documents the levels of harvest, number of nesting females, and hatchling production at Ogasawara and explores, for the first time, their influence on population dynamics of Ogasawara's green turtles.