Conservation of Pacific Sea Turtles

Chapter 7. Conservation Project on Yakushima Island: The Biggest Nesting Site in Japan

108 Yakushima Island is 135 km south of Kagoshima City, Kyushu, at latitude 30° 20′ N and longitude 130° 30′ E (Figure 7.1). It is conical in shape with a circumference of approximately 130 km and is 1,936 m above sea level. Its climate is tropical monsoon, but the mountains often get 1 m of snow. Thus, there is variation in temperature and annual precipitation level between the mountainous area and lowlands. Yakushima Island is surrounded by the East China Sea and the Pacific Ocean. The Kuroshio Current hits the island’s southern coast and meanders into the Pacific Ocean. Sea Turtle Nesting Sites on Yakushima Island Among all the nesting populations in Japan, 30% to 33% of loggerhead (Caretta caretta) females nest on Yakushima Island (Kamezaki et al. 2003), likely making it the largest nesting site in Japan. Moreover, there are some green turtles (Chelonia mydas) that nest on Yakushima, which is the northernmost limit for green turtle nesting in the Pacific. The Nagata District, located in the northwest region of the island (Figure 7.2), is known for its sea turtle nesting beaches. A perennial stream, the Nagata River, runs from the second tallest mountain in Yakushima, Nagata-dake, into the East China Sea, carrying fine sand onto the beach where sea turtles nest. As industrialization progressed on the island in the mid-1960s, civil engineerCHAPTER 7 Conservation Project on Yakushima Island The Biggest Nesting Site in Japan KazuyoSHi oMuta Yakushima Island | 109 ing and construction projects rapidly increased and the sand was mined for concrete production. The Nagata District has three similar beaches, all consisting of coarse granite sand: Inaka Beach, Mae Beach, and Yotsuse Beach. Inaka Beach Inaka Beach, the largest natural sand beach on Yakushima Island, is approximately 1,000 m long and up to 35 m wide. Tourism has developed rapidly in the area; several hotels and camping sites were built near the beach, leaving few grassy areas beyond the beach. Sea turtle watching has become an increasingly popular activity, with thousands of visitors each season. In response to concerns over large numbers of people roaming the beaches to see turtles, an information kiosk was constructed and guided turtle watching tours were organized from May to July in a way that minimizes disturbance of nesting turtles. Inaka Beach historically has the highest nesting success of loggerhead turtles in Yakushima, peaking at approximately 80% in 1986, but it has since declined to 50% to 60% in recent years. Mae Beach Mae Beach, about 900 m long, is located near Nagata Village. Until 1968 the beach was left as natural as it could be, but after a concrete barrier was Figure 7.1 Map of Japan showing Yakushima Island. Figure 7.2 Map of Yakushima Island showing sea turtle nesting beaches in Nagata District. Yakushima Island | 111 built to separate the village and the beach, the sand was mined for the concrete factories and the area became unsuitable for sea turtle nesting. Yotsuse Beach Yotsuse Beach, 240 m long and 40 m wide, formerly was a port for logging. There are two rivers that run into the beach, with heavy rain changing the beach’s appearance. If the rivers were not present, this beach would have been an optimal sea turtle nesting site, because unlike Inaka Beach or Mae Beach, a steep cliff hinders people from approaching the beach. Sea Turtle Monitoring on Yakushima Island By the mid-1980s, the once pristine beaches for which Yakushima Island was famous had been degraded by beach armoring, sand mining, and development (Omuta 1997). Tourism and development have continued to impact the island, and the growing human population has led to deforestation in the mountains. A strong urge to preserve the island’s natural heritage and a deep concern for the future of Yakushima Island motivated me and other local residents to initiate a nongovernmental organization called the Yakushima Umigame Kan (Sea Turtle Center) in 1985 to survey nesting sea turtles. The organization now conducts monitoring and protection work from May to July each year, patrolling the beaches from 9 p.m. to 6 a.m. daily, with some exceptions due to bad weather. The survey consists of a census of sea turtle nesting activity, tagging nesting females, and transplanting clutches that are in danger of poaching or inundation by high tides. Human Interaction with Sea Turtles before Conservation Before 1973, a public bidding system...