BAR HARBOR — Ask a boat cruise naturalist, or just about anyone else who spends time on the water, and he or she will tell you that Mola mola sightings are on the rise this summer.

“I had 10 the other day,” said naturalist Bill Townsend. “We usually see one or two at least. They started showing up early July. And they’re all sizes,” he said.

“They lay on their side because they’re tropical fish, and they lay in the sun,” he said. That behavior earned the species its common name, ocean sunfish. “Usually the top dorsal fin flops up and down. You have to pay attention, but they’re there.”

Townsend, a former park ranger for Acadia National Park, has worked on nature cruises in Frenchman Bay since 1966. “There’s always been a few every summer,” he said, “but their numbers have increased in recent summers.”

Bar Harbor naturalist and educator Megan McOsker agreed. “Yes, there are more Mola mola sightings in the Gulf of Maine. This goes along with a greater presence of one of their major foods, jellyfish.

“Our warming waters are making it harder for some species to thrive,” she continued, “and expanding ranges of some species.”

Enormous and resembling a shark when its fin is sticking out of the water, a mola is a slow-moving fish, harmless to humans.

“If you approach them gentle [while diving],” said marine biologist Tierney Thys in a 2003 televised lecture, “you can give them a scratch and they enjoy it.”

McOsker said she could attest to that. “I swam with one once, near Cashes Ledge,” she said. “It felt slimy on the fin- and then rough on the body. [It was] very big and not threatening at all.”

Under the water, this massive fish has no resemblance to a shark at all.

Video courtesy of NOAA/ONMS/PointBlue/ACCESS

It is flat, roundish, and seems to lack a tail. Though according to National Geographic, the tail is there: it folds in on itself, forming a “clavus” which the fish uses as a rudder. A full-grown mola can reach 14 by 10 feet, and weigh 5,000 pounds.

“Their mouth has fused teeth,” McOsker described, “and when you look into their lovely face you can see their resemblance to their relatives, the puffer fish.”

Though slow and seemingly awkward, molas can dive to depths of over 700 feet in search of food at the ocean bottom.

“They’re up and down 40 times a day,” said Thys, who has tracked molas in the Pacific.

As omnivores, molas eat a balanced diet of crustaceans, sponges, eel grass small fishes and larvae, in addition to their preferred jellyfish.

“I could never see how something that big could get that much nutrition from a jellyfish,” said Townsend.

Found in tropical and temperate waters around the world, molas go by many names. The scientific name: genus Mola, species mola, is Latin for millstone, referring to their round appearance.

Common names in other languages are colorful and varied, most often describing the fish’s appearance. The mola is called “moon fish” in Spanish, “floating head” in German, “lump fish” in Danish, and “toppled wheel fish” in Chinese.

The sunbathing activity is especially common in the northern parts of its range, such as in the Gulf of Maine, as a way to warm itself after diving.

Occasionally molas breach up to ten feet in the air, slapping the water on descent, according to National Geographic. It is thought they do this to rid themselves of skin parasites.

According to the National Oceanic and Atmospheric Administration (NOAA) Fisheries website, molas are found in tropical and temperate seas all over the world. They are pelagic, meaning they roam the open ocean.

“They come from a rebellious little puffer fish faction … that said, oh the heck with the coral reefs, we’re going to head to the high seas,” said Thys.

Mola larvae are tiny — pin-head sized — when they hatch, but they grow quickly. Young molas are seen schooling together, but they “become behemoth loners as adults,” according to Thys.

Locally, mola sightings have been recorded throughout the Gulf of Maine in summer months, as far north as the Gulf of St. Lawrence in Canada. By August, they begin migrating south to warmer waters before winter approaches. Some molas get stuck around Cape Cod and when water temperatures fall below 50 degrees Fahrenheit, they can become “cold-stunned,” according to Carol “Krill” Carson of New England Coastal Wildlife Alliance (NECWA).

NECWA runs a hotline where people can report mola sightings and mola strandings by phone or online.

But while in the Gulf of Maine each summer, molas are a welcome sight to many.

“We can approach them in the big whale watch boats and they will stay on the surface. Passengers love seeing them,” said McOsker. “I don’t like that we have a warming Gulf of Maine but I think that we need to consider the changes that are not necessarily bad — like more Mola mola!”

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