The adolescent fin whale was unable to get back out to deeper waters. (Courtesy of Shawn Johnson, Marine Mammal Center)

A 45- to 50-foot fin whale died after stranding on the north side of Stinson Beach early this morning. Veterinarians are assembling a necropsy team to explore the cause of death.

"What they're doing is trying to see if they can actually pull the animal out of the water higher up on the beach, so that they can safely do a postmortem on the animal," said Kate Harle of the Marine Mammal Center. "We have to figure out how the animal died, first and foremost. And then from there we'll actually figure out how to dispose of the animal correctly."

Experts believe the whale washed up around midnight during high tide. A volunteer with the Marine Mammal Center first spotted the animal at 7:15 a.m. It lived until midmorning.

Harle said that, based on its size, it was probably a juvenile. This is the fourth fin whale the Marine Mammal Center has responded to since 2010. It's the first whale of any species it has responded to at Stinson Beach since 2006.

Fin whales are the second-largest species of whale in the world, and can grow to be 75 feet long. They're an endangered species, typically found in deep offshore waters. They can live to be 80-90 years old.

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Video shows the whale, still alive, thrashing around in the shallow water.

Fin whale washes ashore at Stinson Beach pic.twitter.com/itMLOoKVJY

— Frankie Frost (@FrankieFrost1) August 19, 2013

Fin whale at Stinson Beach is dead. Will be buried at beach. No cause of death, but no external injuries visible.

— Mark Prado (@MarkPradoIJ) August 19, 2013

Molly Samuel contributed to this article.

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45- to 50-Foot Whale Dies on Stinson Beach