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Taiwan clams said threatening native species in Tokyo Bay
Taiwan News, Staff Writer
2014-01-19 04:20 PM
Japanese scientists say a project to revive the population of common orient clams in Tokyo Bay may instead be putting the endangered native species in more danger. The Japanese clams are farmed in Taiwan, then shipped to Japan for dispersal in beaches scattered around Tokyo Bay.

Researchers say they suspect that Taiwanese clams are being mixed in with the Japanese species during the farming part of the operation. The scientists say DNA testing has confirmed that Taiwanese clams have found their way into the bay and pose a threat to Japanese shellfish by taking away their habitat and through cross-breeding.

Massive landfill projects and construction of sea walls in Tokyo Bay as well as many areas around Japan have destroyed much of the native clams’ habitat. In 2012 the Ministry of the Environment designated the common orient clam as a species “at increased risk of extinction.”

Researchers led by Ayako Yamakawa, a lecturer in marine biology at Okinawa International University, examined the DNA of shellfish gathered at 12 sites in Japan, South Korea, China and Taiwan between 2004 and 2013. They concluded that the DNA in six of 62 clams collected on man-made beaches at Kasai Rinkai Park in Tokyo’s Edogawa Ward was identical to the DNA of the Taiwanese variety.

One theory holds that common orient clams now found in Taiwan were originally taken from Japan to the island in the 1920s. Recent studies have shown, however, that more than 8 percent of the DNA of Japanese clams was different from the DNA of the Taiwanese clams.

“It would take the shellfish more than 2 million years to be that much different,” said Yamakawa. “The ones that turned up in the park’s beaches must be indigenous Taiwanese clams.”

A confederation of fishermen’s cooperatives in Chiba Prefecture has been releasing shellfish raised in Taiwan off the shore of Kisarazu in the prefecture as a way to help revive the local common orient clam population. The clams, originally from Kumamoto Prefecture in Kyushu, are sent for farming in Taiwan, which boasts some of the most advanced technology in the field, then transferred to Chiba Prefecture. Chiba Prefectural Government records show that 100 tons of farmed shellfish were released into Tokyo Bay in fiscal 2012. The harvest was 39 tons the same year.

Yamakawa called for a system to determine whether the clams are Japanese or Taiwanese. It would cost¥1,000 (US$9) or less to conduct a simple DNA test per clam, she said. “It would prove a great challenge to remove the Taiwanese shellfish once they settle in the bay,” she said.

Officials in the Chiba confederation have downplayed the suggestion. “We believe that the indigenous species does not exist in Taiwan,” one official says. “We are aware of the contents of the study, but we are not thinking about taking any specific measure now, because we trust the clam farmers (in Taiwan).”

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