Story highlights The ship sunk in more than 6,000 feet of water, an official said

The Coast Guard capsized it by opening fire on the roughly 200-foot trawler

The trawler posed a threat to mariners and the marine environment

The boat is part of a giant debris field making its way toward North America

The shelling and sinking of a rust-stained fishing trawler in Alaskan waters ends its aimless voyage more than a year after a tsunami swept it off the east coast of Japan.

The U.S. Coast Guard said it opened fire on the roughly 200-foot trawler Thursday after it determined the "unmanned, unlit, unmarked vessel" posed a hazard to mariners and Alaska's marine environment.

The Ryou-Un Maru caught fire and capsized in more than 6,000 feet of water about 180 miles southwest of the port city of Sitka, said Petty Officer 1st Class David Mosley, a Coast Guard spokesman.

It was a dramatic end for the Japanese squid trawler. It was bound for a scrap yard before becoming part of a giant debris field generated by a tsunami that struck the island nation following a 9.0-magnitude earthquake on March 11, 2011.

"It's really one of the first significant pieces of tsunami debris to make its way across the Pacific Ocean," Mosley said.

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The ship drifted undetected until late last month when a Canadian coastal air patrol spotted it several hundred miles off the Queen Charlotte Islands, an archipelago on the north coast of British Columbia.

It captured the imagination of the public, which followed the final days of "the ghost ship" in media reports and tracked its progress on Canadian and U.S. Coast Guard websites.

"I think it captured a lot of people because it survived. It was swept away by the tsunami. It's believed lost. It's forgotten about. And it spends an entire year at sea, a summer, a winter and it makes it all the way across the Pacific Ocean," Mosley said.

The Japan coast guard identified the trawler and its owner after Canadian officials provided the identification number on the hull of the ship. It was moored at Hachinohe in the Aomori prefecture when the tsunami hit last year.

The ship drifted into U.S. waters over the weekend, traveling about a mile per hour and making its way toward the rich fishing waters of the Gulf of Alaska, Mosley said.

At that point, the U.S. Coast Guard determined it posed a threat to other ships navigating the area as well as a potential environment hazard, he said.

The U.S. Geological Survey and the National Oceanic and Atmospheric Administration advised the Coast Guard where the ship's sinking would have the least environmental impact.

"The potential for a pollution incident is unknown at this time, but officials have limited concerns about any biological threats due to the length of time the vessel has been at sea," the Coast Guard said in a statement.

The Coast Guard has been continuously broadcasting the vessel's location to mariners. It will continue the warnings through Friday morning until it conducts an aerial survey to determine its sinking left behind no potentially hazardous debris, Mosley said.

The trawler's planned sinking was temporarily halted Thursday morning when the Coast Guard ship, the Anacapa, based out of Petersburg, Alaska, arrived to find a Canadian ship inspecting the trawler.

"They wanted to claim the vessel for salvage," Mosley said.

"At that point, there was a meeting to discuss whether they had the means to tow or salvage the vessel," he said. "They determined it would be too unsafe. At that point, they were asked to leave the area."

The Anacapa opened fire Thursday afternoon with its 25 mm cannons, blowing holes into the side of the Ryou-Un Maru, the Coast Guard said.

It took more than four hours for the trawler to sink.