Oil spilled July 2 from a supertanker in Tokyo Bay amounts to about 1,550 kiloliters of crude, only one-10th the figure reported the night of the spill, Chief Cabinet Secretary Seiroku Kajiyama said July 3.

Kajiyama made the announcement at a hastily arranged news conference. The government had announced late July 2 that between 14,000 and 15,000 kiloliters of crude oil had leaked from the supertanker.

The spill from the Panamanian-registered, Japanese-owned 147,012-ton Diamond Grace spread extensively across the bay since the supertanker ran aground early July 2 about 6 km southeast of Yokohama port’s Honmoku Pier. The drifting slick washed ashore at cargo piers at Honmoku and Daikoku in Yokohama and at Ogishima and Higashi-Ogishima in Kawasaki early July 3, according to the Maritime Safety Agency. But MSA chief Tsutomu Aihara said late July 3 that the size of the spill has considerably dwindled due to cleanup efforts.

Aihara said cleanup crews retrieved more than 570 kiloliters of the spilled oil July 2 and July 3, adding that there now is 19 km of oil fence deployed in the bay. No immediate damage to the fisheries industry has been reported.

The downward correction on the amount of leaked oil was reported to Prime Minister Ryutaro Hashimoto by Transport Minister Makoto Koga, Kajiyama said. Most of the crude initially believed to have leaked was found to have remained inside the hull of the tanker, he said.

The earlier figure was based on a report from Nippon Yusen K.K., co-owner of the Diamond Grace. The actual oil leaked from the tanker — 1,550 kiloliters — was based on a precise check conducted later, Koga said. “After receiving a report on the error, I gave instructions to check the new figure again because we should not make a mistake twice and cause fear among the public,” said Koga, who originally learned of the mistake around 3 a.m.

When the tanker ran aground on Nakanose shoal early July 2, three of the vessel’s tanks were damaged, puncturing the No. 1 and 3 starboard tanks. The ship was transporting crude from the United Arab Emirates. The No. 2 tank was empty.

In the accident, bulkheads separating the tanks were ruptured, and oil contained in the No. 1 and 3 tanks leaked into the No. 2 tank, an MSA official said. Officials could not investigate the internal damage until the tanker was docked at Kawasaki Sea Berth at Ogishima late July 2, they said. Nippon Yusen had believed there was seawater in the No. 2 tank. “Regardless of the size of the spill, we must make our best efforts to clean up the oil,” Koga said.

Hashimoto pledged maximum efforts to contain the spill and to clean it up. “If you look into the details, there are many questions, including why (the captain) mismanaged the tanker,” Hashimoto told reporters at his Official Residence. “But first we have to stop the damage from growing.”

The government will investigate the cause of the accident, Kajiyama said, noting it might simply have been a careless mistake. Nippon Yusen unveiled a report submitted by the tanker’s caption, Hidenori Tsunematsu, that his ship ran aground when it tried to pass between two fishing boats by slowing down. The tanker then was carried by the tide and gusts, it said.

The report said the tanker suffered a strong shock immediately after it started running at dead slow. The pilot on board the Diamond Grace has told of MSA officials that the accident was not caused by mechanical trouble. The MSA has determined the accident was due to an operational error.

The MSA dispatched about 40 cruisers and other vessels for cleanup efforts, while the Maritime Self-Defense Force sent more than 1,400 members aboard 24 vessels. The slick, measuring about 13 km east to west and about 9 km north to south, was drifting with the tide and wind in the area.

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