POINT REYES NATIONAL SEASHORE — Biologists performed a necropsy Tuesday on a 30-foot juvenile humpback whale that washed ashore Sunday at the Point Reyes National Seashore, wading knee-deep in whale intestines in an effort to determine what killed it.

A team of about a half-dozen researchers from the Marine Mammal Center took advantage of the low tide Tuesday at 11:30 a.m. to cut open the whale. It did not have any broken bones, ruling out a boat strike as the cause of death, said Giancarlo Rulli, spokesman for the Marine Mammal Center. There was, however, bruising around the head and neck area on the right side of the humpback, he said.

The cause of death will likely be determined in the coming weeks, Rulli said.

The male cetacean was first spotted by beachcombers Sunday about 2½ miles north of the North Beach parking lot at the Point Reyes National Seashore, said Barbie Halaska, research assistant at the Sausalito-based Marine Mammal Center.

The whale had a full layer of blubber 4½ to 5½ inches deep and appeared healthy, Halaska said.

Of the more than 500 cetacean corpses — whales, dolphins and porpoises — studied by the Marine Mammal Center over 42 years, the cause of death in most instances is unable to be determined because of decomposition, Halaska said.

But the whale on the Point Reyes beach hadn’t been dead long, increasing the likelihood a cause of death will be found. It also makes the humpback a good specimen for tissue samples for the historical record, Halaska said.

The cloud cover and recent foggy days on Point Reyes helped keep the whale from “baking” in direct sunlight, she said.

Once researchers cut open the whale with footlong knives, the smell wafted far down the beach. Researchers wearing waterproof bibs, boots and gloves got inside the young humpback to shift through the stomach contents and intestines. Discarded chunks of whale flesh pulled away from the post mortem site were scattered along the shoreline.

Samples will used to help determine how it died and also will be cataloged on a database on humpback whale life cycles, Halaska said.

“The opportunity to perform a necropsy on a carcass in good condition like this will help contribute to our baseline data on the species,” Halaska said later in a statement.

Five whales washed ashore this year, according to the Marine Mammal Center, a nonprofit research and rescue organization spanning San Luis Obispo County to Mendocino County. On an average year scientists record five to six whale deaths.

The last whale to wash up along the Bay Area coast was a 79-foot blue whale on Agate Beach in Bolinas in May.

As the biologists finished the necropsy around 12:45 p.m. Tuesday, they walked into the surf to rinse off whale blood and guts before hiking out with skin tissue and blubber samples.

The humpback will be left on the beach to let nature run its course, Halaska said.

You can reach Staff Writer Nick Rahaim at 707-521-5203 or nick.rahaim@pressdemocrat.com. On Twitter @nrahaim.