NEW ORLEANS -- Officials are aiming to clean up all the oil from the BP PLC spill from Florida and Alabama beaches before next year's spring tourist season.

The beaches are a popular destination for university students and other visitors during spring break, which peaks around March.

That's a "very aggressive timetable" and some beaches may not meet that goal, said Coast Guard Rear Adm. Paul Zukunft, the federal point man for the disaster.

He said Wednesday there's no set schedule for cleaning the remaining 587 miles (945 kilometers) of oiled shoreline. Scattered areas of heavy oil total about 26 miles (42 kilometers), Zukunft said. He said heavy north winds and beach erosion in Florida exposed tar mats, adding a mile to the heavily oiled total from last week.

"Some of our more persistent oil is in that sand column on both recreational beaches and national park shorelines," he added.

It may be impossible to remove all the oil from some areas, especially Louisiana's delicate coastal marshes, he said.

"If we reach a point where any further cleanup has no net environmental benefit, we will terminate that phase of the response."

About 135 shrimp and fishing boats are still aiding in Gulf of Mexico oil spill cleanup duties, the last of thousands of vessels that joined efforts to combat the largest offshore oil spill in U.S. history,

Coast Guard Rear Adm. Paul Zukunft said another 1,200 boats are waiting to be scrubbed clean after their work in recovery form the April 20 rig explosion and sinking that led to millions of gallons of crude oil gushing into the Gulf from a busted well off Louisiana.

Zukunft said more than 20 drydocks across the Gulf of Mexico are now working to scrub or decontaminate all remaining vessels that took part in operation. "We expect to have all those vessels clean by the end of the calendar year," he said.

About 9,000 square miles (23,000 square kilometers) of federal Gulf waters remain closed to fishing; bad weather kept crews from getting enough species to sample and decide whether to reopen some of that area, Zukunft said.

He added that the spill response cost is now totaling about $27 million a day. At the height of the spill it was about $67 million a day.