Spill Probe Focuses on Depth of Mooring : Environment: New soundings taken at spot where tanker was damaged show water shallower than previously thought. Cleanup crews grow concerned about wetlands.

Cleanup workers patrolled a 25-mile stretch of Orange County shoreline looking for signs of further oil damage Thursday as the investigation into last week’s tanker spill focused on the depth of the offshore mooring area where the accident occurred.

At least three new soundings were taken to measure the depth of the mooring station off Huntington Beach to determine whether the American Trader was in too shallow waters when it struck its own anchor, gashing the hull and spilling 394,000 gallons of Alaskan crude into the Pacific. Results of the soundings were not made available.

Along the shoreline, the cleanup was concentrated on Newport Beach but concern also focused on the newly restored Huntington Beach wetlands where heavy amounts of oily seawater collected at the base of temporary earthen dikes in the mouth of the Santa Ana River. Rock jetties leading to the 25-acre estuary were coated with oil, but none of the tainted seawater reportedly breached a series of protective booms and dikes.

Wildlife officials said fewer oil-soaked birds were being found. By late Thursday, 368 birds had been rescued alive since the Feb. 7 spill and 15 of those were released back into the wild near Point Mugu in Ventura County. Thus far, 216 birds have died, including 13 California brown pelicans, an endangered species.

Several sizeable patches of glistening sheen--a coating of oil often only thousandths of an inch thick--remained just offshore. Late Thursday, the offshore sheen prompted officials to close six miles of shoreline between Corona del Mar and north Laguna. Patches of the sheen also were reported off Newport Beach and the Huntington Beach Municipal Pier.

Some of the oily sheen washed ashore late Wednesday near Laguna Beach in the Crystal Cove area, a rocky stretch of coast dotted with tide pools teeming with marine life. Although it left only a brown film on the rocks, environmentalists fear that any amount of petroleum residue is a threat to sea life.

After an aerial inspection of the coast Thursday, Coast Guard officials said none of the thicker, dark crude that spilled from the 80,000-ton tanker American Trader remained in the ocean.

About 36% of the spilled oil, about 144,600 gallons, was recovered by a flotilla of skimming vessels, while 46%, or 184,800 gallons, were estimated to have evaporated or dispersed in the ocean, Coast Guard spokesman Rick Medit said.

“The rest is on the beach,” Medit said.

Officials said they can do little about the sheen because equipment such as skimmers are useful only when oil is thickly concentrated offshore. British Petroleum, owners of the spilled oil, said the sheen, should it come ashore, does not present a serious threat.

As the investigation into the mooring mishap continued, Golden West Refining, owners of the mooring, began taking new soundings of the area under orders from the Coast Guard. Also examining the bottom were the tanker’s owners, New York-based American Trading Transportation Co. and the federal National Oceanic and Atmospheric Administration.

Coast Guard officials had reported Wednesday that preliminary readings at the mooring indicated that the water may have been as much as five feet shallower than indicated on current navigational charts.

Authorities say the tanker may have been operating in 46 or 47 feet of water instead of the 51 to 53 feet listed on the charts. At the time of the accident, the ship had a draft of 43 feet. Its anchor is four feet wide and about 10 feet long.

With most of the slick now ashore, Coast Guard officials reopened Los Alamitos Bay and the San Gabriel River to boat traffic, but Anaheim Bay, Huntington Harbour and Newport Harbor remain closed indefinitely.

Miles of beach from Newport to Sunset Beach also remained closed for health and safety reasons.

A majority of the 1,400 workers committed to the cleanup effort Thursday worked along a mile-long stretch of beach between Newport Pier and 47th Street still caked with black crude.

About 500 tons of absorbent material used by workers to soak up the oil from the beaches has been taken to a transfer station set up Wednesday on seven vacant acres in Newport Beach. There, workers with the GSX Corp., a toxic waste disposal company, removed some of the moisture from the material in preparation for transfering it to hazardous waste dumps in Buttonwillow, near Bakersfield, or a landfill in the Imperial Valley.

Don McKinnon, a supervisor with GSX, said the transfer station should not present a significant health risk to the Newport Beach area.

Times staff writers Lanie Jones and Ted Johnson contributed to this report.