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Over 150 Years of Data Sheds Light on Today’s Illegal Tortoiseshell Trade

The analysis, which goes back to 1844, shows why the decline of the hawksbill sea turtle isn’t just a modern problem

(Kyle Van Houtan/NOAA)
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The hawksbill sea turtle just might be the most beautiful reptile in the ocean. It’s known for the striking patterns that appear on its head and flippers, but is most prized for its multi-hued shell. That, unfortunately, has also contributed to the reason the species is listed as critically endangered by the International Union for Conservation of Nature (IUCN). With only 25,000 breeding females remaining, the hawksbill is also one of the world’s most endangered sea turtles. Its decline isn’t just a modern problem. A recent study of the tortoiseshell trade suggests that over 150 years, people slaughtered six times as many hawksbills for their shell as previously estimated. And the trade may have paved the way for contemporary illegal, unreported and unregulated (IUU) fishing.

Researchers at the Monterey Bay Aquarium began the study in an attempt to better understand how historical exploitation impacts endangered turtles today. Prior to their research, published in the journal Science Advances, data about the hawksbill trade only went back to 1950, even though researchers already knew the turtle had been exploited for its tortoiseshell much longer. So, the team dove into the archives of a dozen countries, tracing trade records from 1844 to 1992. Among those records were documents from the Japanese customs archives.

The data shows more than 1,186,087 pounds of tortoiseshell made it to market prior to 1950, representing about 880,000 individual turtles that did not appear in previous estimates.

Andrew Masterson at Cosmos reports that a previous report prepared for the IUCN in 2008 estimated that between 1950 and 1992 1.4 million turtles were killed in the trade. Of that number, Tina Deines at National Geographic reports, it’s believed three quarters of the turtles taken were killed between 1970 and 1985 in Belize, Indonesia, Malaysia, Honduras and the Philippines.

Previous estimates all relied on the assumption that the turtles would have been large adults. But the study researchers challenged that hypothesis, finding that over time, as the larger turtles were hunted for their shells (since they primarily eat sponges toxic to humans, their meat is not edible), harvests would have expanded to include more young adult and juvenile turtles, a process known as “fishing down.”

Using data from contemporary shipments of illegal tortoiseshell, which reflected the number of juvenile turtles in those harvests, the team then recalculated the number of turtles harvested over 150 years coming up with four scenarios based on which turtles were targeted. All of the scenarios are apocalyptic, with millions of turtles killed to make combs, eyeglasses, guitar picks and other geegaws.

If only large adults were targeted, the global population of turtles exploited would rest around 4,640,062 individuals. That number jumps to 5,122,951 individuals, however, if mixed adults—where a normal distribution range of adult turtles—are considered. Meanwhile, it balloons to 9,834,837 under the mixed age scenario, where adults and juveniles are harvested and 8,976,503 under the “fishing down” scenario.

David Godfrey, executive of the non-profit Sea Turtle Conservancy, tells Deines that the high numbers the researchers found aren't surprising. “It’s not overly shocking to hear that the numbers were so large because we know how seriously the populations declined,” Godfey says.

The historical trade routes for tortoiseshells remain relevant to today’s illegal fishing practices. “We know these IUU practices didn’t just spring up overnight, but likely came from established networks and operators,” Kyle Van Houtan, Monterey Bay Aquariam’s director of science and the senior author of the paper, says in a press release. “We might have, in these 150 years of tortoiseshell data, found the beginnings of the networks and operators of IUU fishing today.”

Despite being protected internationally since 1977, hawksbills are still illegally caught in places like Indonesia, Malaysia and the Philippines, where they are often exported to China. In turn, the study calls for more oversight of artisan coastal fishing and commercial fleets to protect the turtles and other endangered marine life.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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