( CNN ) -- The U.S. Coast Guard sank a Japanese fishing trawler off the coast of Alaska on Thursday , more than a year after it was swept away by a tsunami off the east coast of Japan , authorities said . The trawler capsized hours after the Coast Guard set fire to it , causing it to begin taking on water , said Petty Officer 1st Class David Mosley , a Coast Guard spokesman . The sinking of the Ryou-Un Maru brought about the end of a journey for the rust-stained ship that drifted across the Pacific Ocean as part of a giant debris field generated by a tsunami that struck Japan following a 9.0 earthquake on March 11 , 2011 . The Coast Guard determined the trawler posed a threat to other ships navigating the area , and had been broadcasting the unmanned , unlit vessel 's location to mariners to alert them to the hazard . The U.S. Geological Survey 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 opened fire on the Ryou-Un Maru at 1 p.m. Thursday . The ship drifted from Canadian waters into U.S. waters on Saturday , and was located about 180 miles west of the Dixon Entrance in Southeast Alaska , the Coast Guard said . The trawler was first spotted floating near British Columbia by a Canadian military air patrol , and it was then determined that it had been adrift since the tsunami , Canadian officials said last month . The Japan Coast Guard identified the owner of the vessel after being contacted by Canadian officials , who were provided the identification number on the hull . The vessel , which was used for squid fishing , was moored at Hachinohe in the Aomori prefecture when the tsunami hit , Japanese authorities said . A Canadian vessel , the Bernie C , had expressed an interest in salvage , which delayed the operation , but officials deemed that it would be too unsafe to tow or attempt to salvage the vessel , said Coast Guard spokesman Kip Wadlow . CNN 's Leslie Tripp , Tina Burnside , Jake Carpenter , Jack Maddox and Jethro Mullen contributed to this report .
NEW : U.S. Coast Guard official says Japanese trawler has capsized . NEW : It sank about 180 miles west of Southeast Alaska , an official says . Authorities say it is a navigation hazard . The boat is part of a giant debris field making its way toward North America .