A "probable ship strike" killed a humpback whale that washed up in Pacifica earlier this week, scientists performing a necropsy on the mammal said Wednesday.
Laura Sherr, spokeswoman for The Marine Mammal Center in Sausalito, said the whale had "four fractured vertebrae with surrounding hemorrhaging, and one broken rib," that led scientists to their conclusion. "This happens occasionally," she said.
Later in the day the scientists realized they couldn't come to a final conclusion about the cause of death because they couldn't find any more broken ribs.
“Every whale stranding is an incredible opportunity to learn from these amazing animals and contribute to baseline data," said Lauren Rust, research biologist at The Marine Mammal Center. “The injuries are consistent with trauma, but it’s likely we’ll never know what truly caused this specific animal’s death."
Ship strikes are a leading cause of whale mortality as it relates to human factors, along with entanglement in fishing gear, the mammal center reported.
In California, Rust said ship strikes of gray whales are the most commonly reported followed by fin, blue, humpback and sperm whales. When large vessels such as container ships are involved, the ship's crew not even know they've hit a whale, making the number of ship strikes to whales likely underreported, she said.
With strong winds at their backs and the ocean waves lapping aggressively behind them, scientists from the mammal center, the California of Academy of Sciences and the University of California at Davis dressed in rubber pants and dug sticks and their hands into the carcass of the whale for most of the morning.
The adult 42-foot female humpback whale was spotted on Monday at Sharp Park State Beach, about half a mile away from where an adult sperm whale washed ashore on the same beach, but closer to Mori Point, on April 15. Previously, scientists thought the whale was 32 feet and a juvenile.
Sue Pemberton with the California Academy of Sciences told NBC Bay Area that this particular beach is often a natural dumping ground for what the ocean throws at it because of onshore winds and where it is located.
"It lends itself to being a repository for dead marine mammals and garbage," she said. " I'm not surprised. Animals die."
Tanya Schevitz, who just moved to Pacifica near the beach, took her two sons, Cash and Catcher Ashkinos, out of school to watch science in the making. They spent the morning taking photos of scientists inside the bowels of the whale, and cutting out pieces of bloody blubber.
Scientists still don't know what killed the adult sperm whale — which is about twice the size of the female humpback.
The sperm whale hasn't been moved, according to Police Chief Dan Steidle, because no jurisdiction has yet to claim it.
Steidle told NBC Bay Area that the dispute is whether the first whale's body lies on the property of the city of Pacifica, the federal Golden Gate National Recreation Area that embodies Mori Point, the city and county of San Francisco's Recreation and Park District that owns a golf course nearby, or the state of California.
He said Pacifica is waiting for a ruling to decide who will move the whale and how to move it.
Scientists at the National Oceanic and Atmospheric Administration said the best thing to do is to tow the whale back out in the ocean, but at this point, it may be too late, he said, because the carcass of the sperm whale is deeply embedded in the sand.
As for the humpback found on Monday, Steidle said; "This one is definitely San Francisco's."
NBC Bay Area's Stephanie Chuang contributed to this report.