1300 / 2024-09-20 23:53:59

What we can learn from a long-term census of loggerhead turtle nesting grounds in Japan

loggerhead,,nesting trends,,egg consumption,,LED

Session 72 - Sea turtle and marine mammal conservation: management, academic and outreach perspectives

The nesting sites of the loggerhead sea turtle in the North Pacific are distributed almost entirely in the Japanese archipelago. I compared the nesting trends of the five major nesting sites, namely Yakushima, Miyazaki, Kamoda, Minabe, and Omaezaki, where the local conservation groups have conducted nesting survey for at least 40 years, and considered the causes of deference among them. The general trends were similar. However, when I looked at the height of the mode around 1990 and around 2012, the latter mode was significantly higher in Yakushima and Miyazaki, whereas the other three sites showed the opposite. This is thought to reflect the fact that females of this species get mature at around 40 years of age and return to their natal beach to lay eggs, and that while in Yakushima and Miyazaki 80 to 90 percent of the eggs were consumed locally until the early 1970s, in the other three locations there was no culture of active egg utilization. Among the five sites, only Kamoda did not show a mode around 2012, and instead showed a monotonically decreasing trend. Three facts worth noting in relation to this are that females tagged at nesting sites such as Kamoda in Tokushima Prefecture have been observed multiple times landing on Minabe Town in Wakayama Prefecture, across the sea to the east, that the ratio of nesting frequencies in Tokushima Prefecture and Wakayama Prefecture has steadily decreased from approximately 1 to 0 since the beginning of this century, and that the secular changes in the total number of nests in Tokushima Prefecture and Wakayama Prefecture are very similar to those in Shizuoka Prefecture and Aichi Prefecture. Furthermore, Anan City, which includes Kamota, is the base of the company that was the first in the world to successfully develop blue LEDs, and in recent years, high-intensity street lights have become visible in various parts of Tokushima Prefecture. Taking all of this into consideration, it is believed that many of the loggerhead turtles born on the beaches of Tokushima Prefecture have recently come to lay their eggs on the beaches of Wakayama Prefecture, across the sea, because they dislike the brightness of their native coasts. These results highlight the importance of protecting females, their eggs and darkness at nesting sites in order to conserve sea turtle.