Dozens of turtles recently disappeared from a zoo in Japan, and officials fear they may have been stolen to be sold illegally.

A total of 64 turtles went missing from their enclosure at the Okinawa Zoo and Museum, Agence France-Presse reported Wednesday. The zoo said the turtles are small, measuring less than 8 inches long.

"We feed them twice a week and a keeper noticed their number was clearly low," zoo section chief Kozue Ohgimi told AFP.

Yellow-margined box turtles were among dozens stolen from an Okinawa Zoo. Okinawa Zoo & Museum/Handout

Officials found that some cable ties used for netting over the turtles' enclosure were removed. "The nets were loose enough to enable an adult to sneak into the area," Ohgimi said.

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Officials worry the turtles — considered exotic pets — were stolen to sell on the black market. In total, 15 Ryukyu leaf turtles and 49 yellow-margined box turtles were taken.

"They are traded for high prices," Ohgimi said.

Ryukyu leaf turtles and yellow-margined box turtles are on a red list of threatened species compiled by the International Union for Conservation of Nature, a global organization focused on conservation and sustainability. They are also designated as "natural treasures" in Japan, making it illegal to commercially trade them.

Both habitat loss due to agriculture and the illegal pet trade are threatening the overall survival of both species.

An investigation is ongoing.