Crews from the state's two oil spill response vessels, along with five support ships, worked throughout the day yesterday to clean up a 4.5-mile slick caused when up to 2,000 gallons of Tesoro light crude oil spilled 1.5 miles off Barbers Point.

The oil recovery efforts were halted yesterday afternoon because of high wind and surf conditions. But by then the slick was no longer visible to helicopters — because of clean-up efforts, solar evaporation, and wind and sea currents, company officials said.

The cause of the spill is being investigated by a unified command composed of the U.S. Coast Guard, Tesoro, and the state Department of Health.

Coast Guard Lt. Commander Todd Offutt, representing the federal on-scene coordinator, said a number of conditions would have to be met before any operations can resume.

"The Coast Guard will be looking at that ship," said Offutt. "To make sure that everything's in place and that it's a safe operation."

Tesoro spokesman Nathan Hokama said the spill happened yesterday around midnight when the chartered oil tanker, Front Sunda, was delivering 42 million gallons of light crude to the Tesoro single point buoy that pipes the oil to the refinery.

About 20 minutes into the operation one of the tanker's hose lines uncoupled.

"When that happened they stopped the unloading operation right away and there was no further release," said Hokama.

By that time, however, an estimated 1,000 to 2,000 gallons of light crude had spilled into the ocean, he said. The oil headed southwest, away from O'ahu.

Hokama said the Coast Guard and the Hawai'i Department of Health were immediately notified, and the specialized vessels from the Clean Islands Council and the Marine Spill Response Corporation were brought in.

Curtis Martin, emergency response coordinator for the state Health Department, said all three flyovers in Tesoro-leased helicopters yesterday included a state on-scene coordinator.

"Anytime you have a release into the marine environment, we're concerned," said Martin.

He said the state was looking for seabirds, turtles or any other sea life that may have been affected by the spill.

"Thus far we have not seen anything," Martin said. "The oil that was released was a very thin, light crude oil, so (evaporation by) the sun has been our best ally in this regard. It has actually done a very good job of getting it off the surface of the water."

As far as possible fines or penalties against Tesoro, Martin said those things would be considered separately. "Our responsibility right now is simply to deal with the response and the cleanup, and protecting the environment and marine health."

Frank Clouse, vice president of refining for Tesoro Hawai'i, said the cleanup efforts were concentrated on the leading southwest edge of the film sheen, which was where most of the oil was located.

Clouse said there would be another flyover this morning to see if additional recovery measures are needed.

"Like I say, the oil rapidly dissipated throughout the entire day," said Clouse. "We'll have to do an investigation ... to find out why the couplings separated."

Clouse said the tanker could be ready to resume delivering the oil as soon as today.

But the Coast Guard's Offutt said it's not as easy as opening the hose lines again once the cleanup and recovery have been completed.

He said a number of tests would need to be conducted on the lines to be certain of their integrity.

"Anytime you get something in that coastal zone, we work closely with the responsible party to make sure they're doing what they need to do," he said.

Reach Will Hoover at whoover@honoluluadvertiser.com.