New Orleans, Louisiana (CNN) -- Initial results from test runs of a ship billed as the world's largest oil skimming vessel could come back Monday after a weekend spent plowing the seas atop the undersea gusher in the Gulf of Mexico.

The converted cargo ship A Whale spent the weekend attempting to separate crude oil from seawater in a 25-square-mile area north of the ruptured BP oil well at the heart of the disaster. If the test is successful, the massive vessel could play a key role in efforts to clean up the largest oil spill in U.S. history.

Initial results from tests are expected Monday, Bob Grantham, spokesman for the company that owns the ship, said.

The ship, which swallows water with oil then separates it, can skim about 21 million gallons of oil a day. That's at least 250 times the amount that modified fishing vessels currently conducting skimming operations have been able to contain, according to Taiwanese company TMT shipping, which owns the vessel.

A total of about 550 skimming vessels were out in the Gulf on Sunday, according to a spokeswoman for the Unified Command Joint Information Center in Houma, Louisiana. But with oil still pouring into the sea at a rate of tens of thousands of barrels a day, federal authorities closed a new section of the Gulf off Louisiana to fishing on Sunday.

The latest order from the National Oceanographic and Atmospheric Administration adds nearly 1,100 square miles of federal waters off Louisiana's Vermilion Bay to the off-limits zone. The new closure brings the portion of the Gulf closed to fishing due to the massive BP spill off Louisiana to 33.2 percent, NOAA reported.

The Coast Guard reported earlier Sunday that a shift in weather patterns could send more oil toward sensitive shores in Mississippi and Louisiana, and bad weather over the past few days has significantly hampered cleanup efforts.

"The weather is one challenge you can't defeat," Coast Guard Adm. Paul Zunkunft said.

Ribbons of oil stripe the water for miles, but waves Saturday were still too high for boats to skim oil off the water.

"At the Coast Guard, we do take it personally. It is portrayed as mission failure any time oil washes ashore," he said.

Zunkunft said he will put the skimmers back to work as soon as the sea calms.

Researchers have estimated that between 35,000 and 60,000 barrels (1.5 million to 2.5 million gallons) of oil have been gushing into the Gulf daily since April 20, when the Deepwater Horizon oil rig exploded and sank off the coast of Louisiana.

The A Whale arrived in the Gulf on Wednesday and has been awaiting approval to join in cleanup efforts.

The skimmer works by "taking in oily water through a series of vents, or jaws, on the side of the ship and then decanting the intake," Grantham said. "In many ways, the ship collects water like an actual whale and pumps internally like a human heart."

Zunkunft said he is also calling in reinforcements, including 300 new skimmers in the next two weeks.

For the 12-hour period from midnight until noon Saturday, approximately 7,980 barrels (335,160 gallons) of oil were collected and about 4,155 barrels (174,510 gallons) of oil and 28.3 million cubic feet of natural gas were flared, BP said.

The company said about 25,290 barrels (1,062,180 gallons) of oil were recovered Friday.

CNN's Allan Chernoff contributed to this report.