Beachgoers on California's Santa Catalina Island got a surprise this week when they discovered a dead 15 1/2-foot-long oarfish that had washed ashore there, which is now giving scientists the chance to study one of the most rarely seen animals on Earth.

The fish was discovered Monday on Pebbly Beach near Avalon, California, around 6:30 a.m. with its tail cut off, the Los Angeles Times reported, adding that oarfish are known to sometimes shed their tails in order to lose weight or save energy.

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Scientists are debating whether Monday's earthquake or the warming of the ocean brought the oarfish ashore. (Los Angeles Times)

When alive, it probably weighed 150 to 200 pounds and was likely about 24 feet long with its tail attached, said Annie MacAuley, a marine biologist and president of the California-based nonprofit Mountain and Sea Educational Adventures.

"This is a once-in-a-lifetime opportunity," MacAuley told the New York Daily News. She and her team of researchers dissected the fish and found it had a belly full of krill as well as an empty pocket in its stomach, which means it could have recently stopped eating due to distress or sickness.

Oarfish are the longest known bony fish in the sea and are believed to be the origin of many sea serpent legends, as they can grow to as long as 50 feet, the National Oceanic and Atmospheric Administration says. Little is known about them because they're so rarely seen alive, as they generally live at depths of around 3,000 feet below the ocean surface.

MacAuley and her team posted these photos of the oarfish on Mountain and Sea Educational Adventures' Facebook page:

The beast found on Monday was the third dead specimen to wash ashore on Catalina Island in the past few years, after an oarfish measuring between 14 and 17 feet was found there in June and an 18-footer was found along the beach in October 2013.

Some scientists point to earthquakes as the reason why the fish are winding up along the beach here. "The last two times there have been oarfish coming up, there's been a lot of seismic activity," MacAuley told the New York Daily News, noting that the San Francisco area experienced a 4.0-magnitude quake Monday morning.

Still, she said that that quake was likely too far away to have caused this fish to wash ashore where it did.

Dr. Misty Paig-Train, a marine biologist with California State University-Fullerton, told the Daily News that the fish could have been affected by El Nino, the periodic warming of the Pacific Ocean that can have wide-ranging impacts across the West Coast including unusually warm water currents.

Exactly why this week's oarfish died and ended up on Catalina Island for now remains a mystery, and that's why it's so critical to study these rare creatures, MacAuley said.

"That's why we're doing our due diligence," she told the Los Angeles Times. "There's so little known about oarfish... They only come to shore when they're going to die."

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