Hundreds of the black spotted turtle are regularly discovered at airports around Asia, having been illegally smuggled in luggage aboard commercial passenger flights, Traffic said.
Some are little bigger than a hand, but they can sell for thousands of dollars on the black market.
"Illegal international trade of the black spotted turtle in Asia has escalated over recent years and immediate action is required to stem the flow," Traffic said as it released a report on the reptile's fate.
The International Union of Conservation and Nature lists it as vulnerable, one step away from endangered, and Traffic said the sudden rise in demand for the turtle as a pet in other parts of Asia had made its future much more fragile.
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In the most recent seizure, 230 turtles were found in unclaimed bags at Bangkok's main international airport on May 14, according to Traffic. The luggage had been on a flight from India.
It said Bangkok was regarded as a transit hub, with the turtles then flown to Hong Kong, Taiwan and other places in East Asia where there was high demand for them as pets.
A mature turtle that is about 30 centimetres long can cost more than USD 2,000 in Hong Kong, according to people who follow the trade.
Many turtles around the world are seriously threatened, with those in Asia particularly at risk due to their habitats being destroyed or damaged and demand for them as pets or food.