The Environment Ministry completed Saturday the netting of fish in an imperial moat in central Tokyo and, contrary to a 2000 survey, found nearly 90 percent of the catch to be native fish, not marauding foreign species.

The operation, which began Feb. 27 at the Ushigafuchi moat of the Imperial Palace, was designed to protect the moat’s native species from omnivorous nonnative fish, such as bluegill sunfish and black bass.

Of the 10,851 fish caught, 9,476 — or 87 percent — were “motsugo” or other native species. There were 1,375 nonnative fish, including 1,299 bluegill sunfish and 64 black bass, the ministry said.

The 2000 survey showed that more than 90 percent of the fish in Ushigafuchi were foreign. Experts attributed the discrepancy to a sampling error and other problems in the survey.

While the ministry took the 2000 sample by casting a net only once, it employed various methods this time, such as netting, dragging for and even scooping up fish by hand. The catch was conducted after the water level was lowered to 40 cm.

“The result from 2000 was far from comprehensive. I am not surprised by the latest result,” said Hiroshi Kono, an associate professor at Tokyo University of Fisheries.

The Environment Ministry insists that native species of fish are in danger, pointing out that the number of native fish has not declined in the moats that are free of foreign species.

“The survey revealed an accurate picture for the first time, not that it ran counter to our estimates,” a ministry official said.

The operation had some unintended effects, however.

On hearing of the results of the operation at Ushigafuchi, the Japan Sportfishing Association seized the opportunity to defend the name of black bass, a popular sport fish. The group sent messages to the media affirming that black bass pose no danger to the environment.

The draining of the moat also help retrieve 23 cu. meters of garbage, including three bicycles.

The operation attracted crowds of spectators each day and the ministry kept the public informed of the progress of their operation.

“I believe the operation helped the public become more aware of problems associated with nonnative species,” a ministry official said.

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