An oil spill fouled miles of fragile coastline Thursday, and environmentalists raced to save tarred marine life as local officials questioned the Coast Guard's response to the ship collision that triggered the spill.

About 58,000 gallons of oil spilled from a South Korea-bound container ship when it struck a tower supporting the San Francisco-Oakland Bay Bridge in dense fog Wednesday morning. The accident caused no structural damage to the span, officials said, but the vessel's hull suffered a large gash.

Tides carried a plume of heavy fuel beneath the Golden Gate Bridge and into the Pacific Ocean. By Thursday afternoon, oil had been sighted as far north as Stinson Beach, about 15 miles north of the city, and at least eight beaches in San Francisco and Marin County were closed.

"What we have here are ribbons of oil just going all over the place," Coast Guard Capt. William Uberti, captain of the Port of San Francisco, said after an aerial survey.

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City officials said the Coast Guard initially underreported the size of the spill, believed to be the biggest in the bay since 1988. As late as 9 p.m. Wednesday, Coast Guard officials were still saying just 140 gallons had poured into the bay, according to Mayor Gavin Newsom, who said the city would consider legal action against anyone found liable.

"We would have responded differently if we had accurate information from the get-go," said Newsom spokesman Nathan Ballard. City workers, for instance, would have initially laid more boom lines to contain the oil, he said.

Sen. Barbara Boxer also criticized the Coast Guard's response in a letter sent Thursday to Commandant Adm. Thad W. Allen, saying she was "very troubled by the Coast Guard's delay in delivering accurate information to the public and the city of San Francisco." The senator asked Allen for a briefing on the status of the spill, its impacts and the Coast Guard's efforts in the cleanup.

A Coast Guard log of Wednesday's events obtained by The Associated Press showed the Coast Guard briefed city officials around 1:25 p.m.

However, the log also suggests that both the ship's crew and some Coast Guard personnel vastly underestimated the scope of the spill at first.

About two hours after the collision, engineers aboard the cargo ship estimated about 146 gallons of fuel had leaked.

The Coast Guard began receiving reports from its own personnel that suggested a much bigger spill, including oil washing up on piers miles away, and "oiled birds and wildlife." Yet at 4:49 p.m., more than eight hours after the collision, a team of Coast Guard, California Department of Fish and Game and San Francisco police officials estimated "400 gallons in the water total," according to the log.

Uberti disputed that, saying Coast Guard personnel knew the full extent of the spill by around 4 p.m. He said the Coast Guard and private response firms responded immediately after the incident, and he rejected any suggestion that the crews could have contained the spill more quickly.

"We mobilized as if it was a big spill right away," said Uberti.

A series of factors appeared to contribute to the slow assessment. The ship's crew could not use its normal means of determining how much fuel had escaped because some of the equipment was damaged in the collision, authorities said.

Instead, they were forced to heat the gelatinous remaining fuel and transfer it to a different tank, then measure it, the officials said.

Other normal means of measuring the spill, such as visual assessments by boat or plane, were hampered by the fog, said Lt. Rob Roberts, an investigator with the California Department of Fish and Game.

"It was hard to see what was going on down at the waterline," he said.

Meanwhile, a hazy film of oil surrounded Alcatraz Island, and the plume extended well north and south of the Golden Gate Bridge. Birds were spotted alive and coated in oil, and state officials estimated the number of injured birds was in the dozens. At least six were found dead, the Department of Fish and Game said.

The petroleum was the bunker fuel that powers ships' engines. This heavy fuel is the residue from oil refining and contains many contaminants.

"This is a very environmentally sensitive area, so it's of great concern," said Uberti, who canceled the swim portions of two triathlons scheduled for this weekend because of health concerns.

The coast north of San Francisco ranges from sandy beaches to barren cliffs to sensitive marshes. Environmentalists fear the impact on shorebirds, fish and marine mammals could be felt for months, even years.

"We're looking at almost everything being affected," said Sejal Choksi of the environmental group San Francisco Baykeeper.

Some 9,500 gallons of fuel was recovered, and 18,000 feet of booms were in place by Thursday afternoon, the Coast Guard said. Crews aboard two helicopters surveyed the damage as 11 skimmers sucked up the oil on the bay and ocean. Teams also walked the shoreline assessing and scooping up the oil.

"We can't stop everything, but we're going to do our best," Uberti said.

The ship, called Cosco Buson, is owned by Hong Kong-based Regal Stone Ltd., which had leased it to South Korea-based Hanjin Shipping for the voyage.

Barry McFarley, whose private recovery firm the O'Brien Group was hired by the ship's owner to handle its response to the spill, apologized to the public.

"I'd like to express our concern and regret that this incident occurred and assure the community and the public in the San Francisco Bay area that we're making every effort and (using) every resource available," he said.

Cosco Busan, built in South Korea in 2001, had just left the Port of Oakland carrying container cargo and was proceeding to sea when it hit the bridge. Darrell Wilson, a spokesman for Regal Stone, said the ship was bound for Pusan, South Korea.

Authorities were still investigating the cause of the collision.

The pilot, Capt. John Cota, was interviewed Thursday morning by Coast Guard authorities. He and other crew members were tested Wednesday morning for drugs and alcohol, and the results were negative.

If investigators conclude Cota acted negligently, he could lose his state-issued pilot license, Uberti said.

Cota did not immediately respond to a call for comment.

He is in good standing and is one of the most experienced of the 60 captains who guide ships into the bay, said Patrick Moloney, executive director of the San Francisco Pilots Commission.

Cota has been involved in a few minor incidents during his 25 years on the bay, most recently when he ran aground in San Pablo Bay about a year and a half ago, according to Moloney. He received a letter of reprimand for that incident, according to Moloney.