Marianne Nyegaard, a researcher at Australia's Murdoch University,  saw the species for the first time in New Zealand in 2015 and called it the "hoodwinker" because of its tendency to blend in with other sunfish species and hide in plain sight.

"There are rare finds, and then there are those out-of-nowhere, first-ever discoveries that send scientists' heart aflutter," Shelly Leachman, a spokeswoman for the university, said.

The discovery is remarkable, researchers said, given the fish's furtive nature and because it was found so far from its normal habitat.

Part of the Molidae family, the hoodwinker has a wide body that comes to an end just behind its dorsal and anal fins, giving it an almost flat appearance or that of half a fish. Its "funny-looking pointy fins plopped on it like a bird" make the fish nearly as wide as it is long, said Thomas Turner, who helped confirm the fish was a hoodwinker.

"It's a big, flat oval-shaped fish ... with a constantly surprised look," said Turner, an associate professor in UC Santa Barbara's department of ecology, evolution and marine biology. "It's the weirdest-looking thing you've ever seen."

The fish was first spotted in shallow water by Jessica Nielsen, a conservation specialist at the university's Coal Oil Point Reserve, who was doing research on the beach. Later, an intern found the fish dead on the shore.

The reserve posted photographs of the animal on Facebook, and, because it appeared to be a Mola mola - an ocean sunfish common in the Santa Barbara Channel - researchers left it on the beach, to be recycled naturally.

The Mola mola species is an open-water fish that swims in the depths of the Pacific Ocean. It floats up to the surface to bask in the sun - hence its "sunfish" name. Despite its flat shape, the Molidae are not like flounder, which wiggle along the ocean floor. Instead, the Mola mola - the heaviest fish in the ocean, with some weighing more than 2300 kilograms - swims slowly in the deep ocean.

The Mola tecta is genetically different from the Mola mola, but the physical differences are subtle. The hoodwinker is more slender and has a flap instead of a tail with bony structures along the end of it. The scales are also more like sandpaper, unlike the smooth scales of the Mola mola.

The Mola mola has been found south of the equator, but it's rarer there than in its common swimming grounds in the Santa Barbara Channel.

Turner saw the fish's photo on the reserve's Facebook post and wanted to see the odd-looking animal for himself. So after work, he drove his wife and four-year-old son, Wren, to the beach to check out the sea creature.

The boy was impressed with the animal's scales, which have small pointy spikes all over them, and its toothless, beak-like mouth.

Turner then posted photographs on iNaturalist, a social media site for amateurs and professionals interested in learning about different animal species.

The fish had previously been seen more than 100 years ago - in Holland in 1889, far from its normal warm climes. But it was misidentified as a Mola mola until Nyegaard, the Australian researcher, officially described it in an academic journal in 2017. It was the first species added to the Mola genus in 125 years.

When a fellow scientist alerted Nyegaard that the California researchers might have a hoodwinker on their hands, she said she couldn't believe it.

"I was super sceptical," she said. "I thought, 'It would be so cool if it was one.' "

She suspected the Santa Barbara fish was the new Mola tecta species but was reluctant to make a final determination because the animal was found so far away from its natural habitat.

She advised Turner and the other researchers to examine the fish further and gave them specific instructions on what photographs she would need in order to determine its species.

Nyegaard said she cautioned herself not to get too excited, but when the additional images were sent, she said there was no doubt about the type of fish.

"I yelled out, 'It's a hoodwinker!' I just fell off my chair."

Turner said so little was known about the Mola tecta that researchers don't really know how rare it is. Either the sunfish is actually common in more northern Pacific waters and simply hasn't been seen until now, or the hoodwinker made a long trek to the West Coast, he said.

Regardless, it's odd the fish ended up stranded on the beach, scientists said, adding that Nyegaard's research would help determine what went wrong.

Researchers said the fish had no signs of injury and wasn't obviously in distress. It's possible, Turner said, that ocean warming caused the animal to veer off-course.

The ocean has been unusually warm for years now, causing species to move further north from their normal habitats, said Elliott Hazen, an ecologist with the US National Oceanic and Atmospheric Administration who specialises in water temperature's impact on wildlife.

Just this week, a dead humpback whale ended up in Brazil at the mouth of the Amazon River. Researchers suspected the mammal was lost at sea and died of an unknown cause.

And this isn't the first time out-of-place sea creatures have washed up on Southern California beaches. In January 2018, a rare venomous sea snake more common to the coasts of Africa, Asia and Central America, was discovered on the shore in Newport Beach. And a giant oarfish, normally found at ocean depths of 900 metres, washed ashore on Catalina Island in August 2015.

Hazen suspects these rare occurrences have to do with fluctuations in ocean temperatures. Changes in weather patterns - such as an El Nino or La Nina event - can either warm or cool the waters around the equator, allowing species to cross that normal barrier.

Extreme changes in water temperatures can also lead to sickness in sea creatures.

"The equator acts as a barrier to migration for fish species," Hazen said. "[Species] like marlin, they will swim right up to the equator and just kind of bounce back. But when there's warming or changes in ocean currents that are not normally seen, you can get these species that cross that barrier when they normally wouldn't.

"Large species, such as the humpback whale found in the Amazon, have very good navigational skills," he said. "But when they get sick, they can lose that sense of direction."

Los Angeles Times