A recent local study found that exposing some conserved sea turtle eggs to predators could help stabilize Orchid Island’s (Lanyu, 蘭嶼) ecosystem, the National Museum of Natural Science said in a statement on Monday.
While efforts have been made since the 1990s to help sea turtles reproduce on the island off the eastern coast, research conducted over a 23-year period has found that the ecosystem is in jeopardy because of a strategy to protect sea turtle eggs from predator reptiles, the museum said.
The discovery was made by a seven-member research team led by Huang Wen-san (黃文山), deputy director of the museum located in Taichung, highlighting the crucial role sea turtles play in Orchid Island’s ecosystem.
Photo: CNA
“Sea turtles provide essential links between marine and terrestrial ecosystems, transporting nutrients and energy from the ocean to the land by nesting in beach habitats,” the team wrote in an article named “Loss of sea turtle eggs drives the collapse of an insular reptile community” and got published in Science Advances in December last year.
However, marine eggs have become less accessible to predators due to two anthropogenic factors, they said.
First, sea turtles have fewer nesting sites due to the increasing number of people living on the island and the impacts of climate change, including rising sea levels and more frequent storms, which have led to beach erosion, they said.
Second, “predator exclusion,” a common management strategy deployed in sea turtle conservation, has also played a role, they said.
Effective as this strategy is in sheltering turtle nests from predators, the team observed that “this practice also prevents native predators that have coevolved with sea turtles from accessing eggs and thereby stops the input of oceanic nutrients into the terrestrial community.”
Taking Badai Beach, a smaller beach on the island, as an example, the research team said that since 1997 different exclusion fences have been used to keep snakes away from sea turtle nests on beaches.
That measure has led to the almost complete exclusion of sea turtle eggs from the island’s food chain since 2001, regardless of the species’ historical link to its ecosystem.
With no more sea turtle eggs to feed on, predators such as kukri snakes and stink rat snakes were forced to prey on the eggs of local lizards, consuming 5,000 to 18,000 eggs annually, the team said.
That snakes are preying on lizard eggs is corroborated by the relatively stable populations of the same lizard species on nearby Green Island and in Pingtung County, where sea turtle eggs are not present, the team added.
The number of the long-tailed sun skink on Orchid Island has declined significantly since 2002, with models estimating a population decline of 27 percent to 36 percent a year, while the decrease in population on Green Island and in Pingtung has never exceeded 5 percent a year, they said.
The outcome led the team to reflect on how appropriate the sea turtle conservation strategy was, given that during 1997 to 2000 period, the estimated number of lizard eggs consumed by kukri snakes was about 120 sea turtle eggs a year, a relatively small portion of eggs laid, they said.
Huang said annually there were about 20 sea turtle nests with more than 100 eggs in each.
Therefore, instead of keeping sea turtle eggs completely out of the reach of snakes, Huang’s team called for a “more comprehensive approach that considers how conservation actions will affect interspecific relationships, particularly in cases involving cross-ecosystem interactions.”
Making some sea turtle eggs accessible to predators could help maintain the stability of Orchid Island’s ecosystem, the team said.
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