As the Coast Guard responded to the sinking of a 90-foot tugboat and the potential spill of thousand of gallons of fuel, federal wildlife officials corralled three monk seals from the Leeward Coast. The seals were taken to the National Oceanic and Atmospheric Administration's facility on Ford Island until the threat was over. "We actually removed one monk seal and are in the process of removing two others to bring them into captive care," said David Schofield, Marine Mammal Health and Response Program Manager at NOAA. "These seals are currently healthy, they show no signs of being oiled." The Coast Guard on Friday conducted a helicopter tour of the area where the tugboat Nalani sank. While the aerial survey found no spills there, other ships reported seeing a mile-long sheen about seven miles off of Honolulu Airport. Coast Guard officials said they're unsure of the source of the sheen but have dispatched crews to contain it. Meanwhile, NOAA said it sent one of its own ships into the area to look out for other marine animals. "We do have a team out on a NOAA vessel out. It is searching for turtles, dolphins and whales that may be in the and around the area," Schofield. Diesel fuel can cause respiratory complications and damage to the mucus membranes when it's breathed in by marine mammals. It's toxic if it's ingested, Schofield said.