The Effect of Light Pollution on the Sea Finding Behavior of Green Turtle Hatchlings on Lanyu Island, Taiwan.

octurnal animals use their vision and acute hearing to adapt to the nighttime environment. Light pollution has become a serious problem for nocturnal animals in coastal areas, especially nesting sea turtles and sea turtle hatchlings. Hatchlings use visual clues to find the ocean. However, when the artificial light is stronger than the natural light, hatchlings become either misoriented, disoriented or both. Due to rapid tourism development on Lanyu Island, new sources of light pollution, especially streetlights, pose a serious threat to sea turtle hatchlings. In this study, we used a portable lamp constructed by Liteon Inc. on a circular area of a turtle nesting beach to see how artificial light sources could affect green turtle hatchlings' sea finding behavior. In the experiments, we tested hatchling behavior under different lamp settings (strong or weak light intensity; white or yellow light; lamp shield presence or absence) and moon visibilities (moonlit or moonless). The hatchlings' crawling tracks and locations at the end of the trials were recorded. Results showed that the light intensity had no effect on hatchling sea finding behavior. White light had a stronger impact on hatchling sea finding behavior than yellow light. When the lamp shield was installed on moonlit nights, more hatchings were able to find the sea under both white and yellow lights. Thus, it is recommended that light shields be installed on the streetlights of Lanyu Island in order to protect the sea turtle hatchlings effectively.

Twenty-three Years of Sea Turtle Stranding/ bycatch Research in Taiwan.

Coastal sea turtle stranding and bycatch are common phenomena worldwide and have received more attention in recent years. They are caused by both natural and anthropogenic factors. One thousand and seventy-two turtles were reported to be victims of these phenomena from March 1997 to November 2019 in Taiwan. Number of stranding/bycatch were variable and infrequent for the first 14 years, but increased each year after 2012 and peaked in 2019 with 217 cases. Most turtles were juveniles to subadults. All five of Taiwan's species were reported in stranding and bycatch records, and the green turtle was reported the most common. The main reported seasons lasted from winter to spring, when the weather changes dramatically. The sex ratio (female: male) ranged from 7 in the hawksbill turtle to 0.7 in the olive ridley, with an average of 2.4 for all species. Green turtles were the dominant stranded species, and more loggerhead turtles were by-caught. The hotspots were the towns of Dougou and Tochen in Yilan County, and Gongliao District in New Taipei City, located in NE coast of Taiwan respectively. Stranding was the more common of the two phenomena reported, and 80% of all stranded turtles were subadult green turtles. Eighty percent of all stranded/bycaught turtles were dead. Pond-nets were the fishing gear that accounted for the most bycatch, and captured mainly living young and subadult green turtles as well as subadult loggerhead turtles. The hotspots for bycatch were the towns of Dongou and Tochen in Yilan County. The Coast Guard and concerned citizen were the main sources of reports. This is the first study to analyze the long-term stranding/bycatch of sea turtles in Taiwan.