EASTPORT, Maine — When undersea diver Scott MacNichol of Perry first saw the large shape circling him in Broad Cove on Saturday afternoon, he knew exactly what it was: a shark, a big shark.

MacNichol, 30, was about 28 feet down in the cove, also known locally as Burnt Cove, filming the ocean bottom and taking samples from an empty salmon pen. He estimated the shark was 8 feet long and 300 pounds.

“That shark wasn’t there for the salmon. There were no fish, no food,” he said.

But the shark was clearly interested in MacNichol and proved incredibly aggressive, he said.

“It circled me two times and then began jabbing at my camera,” MacNichol said.

Video courtesy MER Assessment

“All of I could think of, honestly, was my boy,” MacNichol said, referring to his 3-year-old son, Brayden.

“I’ve seen plenty of sharks around here chasing mackerel and herring. That’s not uncommon,” said MacNichol, who has been diving for 17 years. “But this is the first time I’ve seen one while diving. And the first time one came after me.”

Unhurt in the incident, MacNichol stayed out of the water for a couple days, but dove again Tuesday. “I went back to the same spot, and the shark was gone,” he said.

MacNichol was filming the ocean floor under the empty salmon pens for Cooke Aquaculture.

Company spokesman Nell Halse said Tuesday that the company hired MER Assessment Corp. out of Brunswick to film the seafloor and obtain samples as part of Cooke’s environmental protection requirements.

She said divers are routinely inside the salmon pens, testing nets and sampling fish, but MacNichol’s work this weekend took him outside the pen.

“He was forced to use his camera to fend off the shark,” she said. “The shark just wouldn’t leave him alone.”

Once MacNichol came to the surface he quickly climbed into the waiting MER boat. On board was his boss, Chris Heinig.

“When Scott surfaced, the shark was literally draped over him,” Heinig said. “This was incredibly unusual.”

MacNichol, Heinig and another diver waited more than an hour and then the second diver entered the water.

“After about 15 minutes, Scott and I could see the shark under the boat,” Heinig said. “We began slapping the boat and the water with the oars and shouting to alert the diver to his presence. Not surprisingly, the diver came flying out of the water.”

That diver was not hurt either.

Heinig said the shark was a porbeagle, a cold-water shark that can travel south from Nova Scotia along the Maine coast. “It is a small fish eater and doesn’t eat seals,” Heinig said. “So I believe the shark was attacking Scott’s camera.”

Heinig said, “This was not at all an attack on a human. It was a matter of the shark trying to figure out if the camera was lunch. The shark probably thought the camera was one nice morsel.”

Heinig said the underwater camera is encased in a silver-colored aluminum housing, which includes batteries that emit an electrical field and a high-intensity light.

“Sharks are very sensitive to electrical fields,” he said.

Heinig, who has been conducting underwater assessments for 20 years, surmised that the shark was lured into the bay as it chased either herring or mackerel. When it spotted the shiny camera case, it thought it was fish and then became confused.

“We had a similar incident in Machias Bay about six years ago, but that was a great white shark. That diver also was not injured,” he said.

“This encounter is very unusual, and we have been hearing reports of a number of sharks in the bay area this summer,” Halse said.

Capt. Tom King, a shark fisherman out of Scituate Harbor, Mass., who is considered New England’s shark expert, said Tuesday that the incident “is certainly of interest and should not be minimized.”

But no one should be alarmed, Tony LaCasse, spokesman for the New England Aquarium in Boston said.

“The big sharks that people are most concerned about, such as the great white, stay off Cape Cod. There are thousands of gray seals there, which is their preferred food. They rarely go as far north as Eastport, Maine.”

History disputes that, however. According to the Discovery Channel, the world’s largest accurately measured great white shark was 20 feet long, caught off Prince Edward Island in Canada in 1988.

For sharks, it’s only a hop, skip and a jump from Prince Edward Island to Eastport.

LaCasse pointed out that no one has been killed in a shark attack in New England since 1936.

“You have a far greater chance of dying in a car crash on your way to the beach than being killed by a shark,” LaCasse said.

Maine doesn’t have a shark expert in the Department of Marine Resources because they aren’t considered a problem here. Two sharks were spotted in June about 10 miles off the coast at York, but Coast Guard officials said they have not received a report of any other sightings.

Chief Petty Officer Randy Bucklin of the northern Coast Guard division which encompasses Down East said a shark in Johnson Bay would be “most unusual, especially this late in the season.”

According to King, the most common species of shark in the Gulf of Maine are spiny dogfish, blue shark, basking shark, shortfin mako, porbeagle, thresher, sand tiger shark and great white shark (listed in descending order of abundance). Most of these normally would never be encountered less than 20 miles offshore.

Until this summer.

Capt. Robert Peacock, who has worked the waters off Eastport for years, said he saw his first big shark in Head Harbour Passage — between Eastport and Campobello Island — this summer. He could not identify the species.

“It was 8 to 10 feet long and black,” he said.

Sharks also were commonly spotted this season by people on whale-watching cruises.

Lobsterman Darrell Kelley out of Beals Island said warm water temperatures after an unseasonably hot summer may have brought the shark into the bay. Eastport waters were 51 degrees this weekend.

“Sharks will chase bait fish,” Kelley said. “A shark will go anywhere if the water temperature is reasonable.”