Biologists perform a necropsy on a blue whale Saturday after towing it to the California coast. Two broken ribs and a smashed cranium were found during the exam.

The blue whale found dead last week in the Santa Barbara, Calif., Channel was likely the third victim in two weeks of a ship collision, scientists said Saturday as they conducted a post-mortem on the 60-ton creature.

As surf roiled around the massive carcass on a beach at Point Mugu, biologists cut doorway-size openings in its belly and probed its organs for tissue specimens. About an hour after they had peeled back four-inch-thick sheets of snowy blubber, they started removing foot-long bone fragments that had chipped away from the animal’s nine-foot ribs. Later, they found other fractured bones, including a smashed cranium.

“It’s definitely a ship strike,” said Easter Moorman, a spokeswoman for the Santa Barbara Museum of Natural History, which was directing the necropsy of the not-quite fully grown male. “The animal died instantly.”

Three blue whales – members of the largest species on Earth – have been discovered dead off Southern California in the last two weeks, the most recent on Wednesday. Two found in the Santa Barbara Channel were thoroughly examined by scientists, who concluded they were hit by ships. One found in Long Beach Harbor was towed out to sea, but a biologist who viewed it said it probably had been hauled into port on a ship’s bow.

A blue whale washed up in Ensenada, Mexico, but scientists are divided as to whether it might have been the one originally seen in Long Beach.

The questions looming over this puzzling and highly unusual succession of deaths await extensive laboratory testing of the samples extracted Saturday. The tests, which may take months, could point to an illness or infection that afflicted the whales as they swam through the busy shipping lanes off Southern California. Tissues from the other whales were too far gone for analysis.

One possible cause for the deaths is domoic acid, a substance created by algae, and which is known to have killed dolphins and sea lions off the California coast.

Scientists also want to know whether Navy sonar exercises off San Diego might have played a role.