2017-09-20 18:30:03
Trilobites: Sea Turtles Appear to Be Bouncing Back Around the World

18:30, September 20 126 0

On this planet, so many plants and animals are disappearing that scientists worry we’re experiencing a sixth mass extinction. Many of these organisms are taking hits from a variety of angles — habitat loss, climate change and more — that it’s hard to get a grasp on how to stop their declines. Conservation success stories are rare.

But sea turtles may be an exception, according to an comprehensive analysis of global sea turtle abundance published Wednesday in Science Advances.

Antonios Mazaris, an ecologist at Aristotle University of Thessaloniki in Greece and a team of international researchers found that globally, most populations of sea turtles are bouncing back after historical declines. Their research helps clarify why some conservation and research groups have reported both increases and decreases for individual nesting sites over the past decade.

Dr. Mazaris and his colleagues analyzed existing public data of sea turtle nesting sites around the world over time periods ranging from six to 47 years. They standardized individual data sets and evaluated each site separately and then combined them into regional populations to look at changes. Even small populations, which normally have a tough time recovering, are capable of being restored, they found.

But they also learned that some sea turtles are still declining — like leatherbacks in the Eastern and Western Pacific. Their findings support assessments made by the International Union for Conservation of Nature, which lists six of seven species as vulnerable, endangered or critically endangered.

In contrast with some other at-risk species, perhaps sea turtles have been easier to manage because their threats are more tangible: They are accidentally trapped by fishermen or harvested by others as delicacies, aphrodisiacs or decoration. In the most extreme cases, like in Tortuguero, Costa Rica, nearly all female green turtles at one point had been exported for turtle soup.

But conservation efforts there dating back to the 1950s made an impact, and protecting beaches, regulating fishing and establishing marine protected areas have helped save turtles in many locations. This isn’t often the case in conservation stories of animals, like endangered caribou, which face threats that are more difficult to manage.

But to truly know how well conservation is working, the researchers found, it’s best to look at long-term trends (although short-term data has its uses). That’s because most sea turtle species only nest when foraging is good, and from year to year, the number of nests found on a beach can vary dramatically. Detecting whether a juvenile sea turtle survives long enough to make babies can take 10 to 30 years while it matures.

They were surprised to find that with adequate protection, even small populations of turtles have a chance of survival. In an area called French Frigate Shoals in Hawaii, for example, green sea turtles increased nest numbers from around 200 in 1973, when the Endangered Species Act was signed, to around 2,000 in 2012. This species is now considered of “least concern,” by the International Union for Conservation of Nature.

Yet research is still lacking. For all sea turtles, most male to female ratios are unknown, which is an important aspect of reproduction and appears to be altered with increasing sand temperatures, skewing births toward more females. And a huge initiative to collect more data on flatback turtles in and around Australia may be complicated by a recent announcement that the country will shrink its marine protected areas.

Dr. Mazaris said his paper is a tale of “cautionary optimism.” He commends conservationists working to save turtles over the past 70 years, but “long term efforts need to be supported.”