A shark expert said Friday that a shark that was seen five miles off Boothbay Harbor this week was probably a great white, the world’s largest predatory fish, and that its presence indicates the species is expanding its range into Maine waters.

James Sulikowski, associate professor in the University of New England’s marine science department, watched the video taken by lobsterman Ryan Casey on Tuesday and immediately said, “Oh my God, that’s a white shark.”

Sulikowski said he based his identification on the size of the fins, the size of the head and the way the shark was feeding on a whale carcass.

While several shark species inhabit Maine’s coastal waters and would feed on a whale carcass, the white shark has a distinctive way of raising its head and then letting the upper jaw drop onto its food, Sulikowski said. That reflects the larger, longer teeth of a great white shark.

A blue shark, for instance, has smaller teeth and is more likely to thrash its head from side to side as it shreds its food.

The presence of a great white shark off the coast of Maine didn’t surprise Chris Fischer, founder of OCEARCH, a shark research organization.

Scientists working with the group have tagged sharks off Cape Cod, then tracked them into the Bay of Fundy in Canada, “so they know they’re moving through the Gulf of Maine,” he said.

Fischer just launched a month-long expedition to attach tracking tags to 10 to 20 great white sharks off Cape Cod so their movements can be tracked remotely.

Fischer said he supports shark research because of the creatures’ importance to the ecosystem as predators at the top of the food chain, helping to keep the population of other animals in check.

Millions of sharks are killed every year so their fins can be used in soup, he said.

For tourism, great white sharks aren’t necessarily a good thing, said Vaughn Stinson, chief executive officer of the Maine Office of Tourism.

Although humans have had no problems with sharks in the 15 years he has been in Maine, “I would not consider it positive PR if someone said a herd of great whites was off York Beach,” he said.

Stinson said the sharks are an exciting draw for whale-watch boats in the Gulf of Maine, but “I would certainly prefer they stay way away from Maine shores.”

On Wednesday, a person who was fishing off the jetty in Wells reported seeing what appeared to be a shark close to shore. Authorities searched the area but found nothing, and have not confirmed that was a shark.

Sulikowski, who travels extensively to study sharks, was excited by the video taken off Boothbay Harbor because it suggests that the white shark is expanding its range north into Maine waters.

“It’s completely awesome, just from an ecological perspective, to have a majestic creature in our waters, utilizing this area for some part of its biology,” he said.

“I would be highly surprised if this was an isolated incident. … Honestly, it’s only a matter of time before we get a larger white population,” he said. “They’re coming for food and we have a healthy seal population.”

The warming of waters in the Gulf of Maine has led to more shark activity earlier in the year as they chase food moving closer to the coast, Sulikowski said.

Seals are a primary food source for white sharks and are cited as the reason white sharks have been congregating around Chatham, Mass., on Cape Cod, he said.

Great white shark attacks on humans are extremely rare, he said.

“You have a much greater chance of dying by getting hit by a toilet seat in a freak accident, struck by lightning, you name it, than being attacked and eaten by a shark,” he said.

Sulikowski focuses his research on porbeagle sharks. The Gulf of Maine appears to be a nursery for those sharks, borne out by researchers’ ability to catch juveniles just 3 feet long, he said.

Maine has experience with great whites.

According to “Fishes of the Gulf of Maine,” a fishery bulletin put out by the U.S. Fish and Wildlife Service in 1953: “We find scattered records from the vicinity of Portland, Maine, most recently, a 13-footer caught in a gill net off Casco Bay in November 1931.”

The report adds, “a very large one (estimated as about 26 feet long) taken in a weir at Campobello Island, November 23, 1932.”

“It was suggested locally,” the report says, “that it may have been the same specimen that had attacked a fishing boat off Digby, Nova Scotia, the preceding July.”

David Hench can be contacted at 791-6327 or at: dhench@pressherald.com